Techi yard

Microcontroller - Introduction

2015-01-04T01:40:00.000+05:30

Microcontroller

Microcontroller can be termed as a single on chip computer which includes number of peripherals like RAM, EEPROM, Timers etc., required to perform some predefined task.

There are number of popular families of microcontrollers which are used in different applications as per their capability and feasibility to perform the desired task, most common of these are 8051, AVR and PIC microcontrollers.

With microcontrollers in general, it is good to know that these little chips are found everywhere. You can find them in microwaves ovens, new applicances, automobiles, televisions, etc. These microcontrollers control and sense the surrounding electronics and environment. For example, microcontrollers can provide output to a display, motor, LEDS, etc., sensing the environment, such as tilt using an accellerometer, light, angular velocity using a MEMS (Microelectromechanical System) gyroscope, sound, encoders for movement, temperature, and button or keyboard input.

To give you a basic understanding of the microcontroller, the AVR Atmega32 microcontroller is considered to be a computer on a chip. The microcontroller is able to execute a set of instructions in the form of a program. The program language that I will be using for theseprojects is C++. To giv ethe usersof this website the best opportunity to learn, the C++ programs will be explained is great detail.

AVR

AVR was developed in the year 1996 by Atmel Corporation. The architecture of AVR was developed by Alf-Egil Bogen and Vegard Wollan. AVR derives its name from its developers and stands for Alf-Egil Bogen Vegard Wollan RISC microcontroller, also known as Advanced Virtual RISC. The AT90S8515 was the first microcontroller which was based on AVR architecture however the first microcontroller to hit the commercial market was AT90S1200 in the year 1997.

AVR microcontrollers are available in three categories:

1. TinyAVR – Less memory, small size, suitable only for simpler applications

2. MegaAVR – These are the most popular ones having good amount of memory (upto 256 KB), higher number of inbuilt peripherals and suitable for moderate to complex applications.

3. XmegaAVR – Used commercially for complex applications, which require large program memory and high speed.

The following table compares the above mentioned AVR series of microcontrollers:

Series Name	Pins	Flash Memory	Special Feature
TinyAVR	6-32	0.5-8 KB	Small in size
MegaAVR	28-100	4-256KB	Extended peripherals
XmegaAVR	44-100	16-384KB	DMA, Event System included

What’s special about AVR?

They are fast: AVR microcontroller executes most of the instructions in single execution cycle. AVRs are about 4 times faster than PICs, they consume less power and can be operated in different power saving modes. Let’s do the comparison between the three most commonly used families of microcontrollers.

	8051	PIC	AVR
SPEED	Slow	Moderate	Fast
MEMORY	Small	Large	Large
ARCHITECTURE	CISC	RISC	RISC
ADC	Not Present	Inbuilt	Inbuilt
Timers	Inbuilt	Inbuilt	Inbuilt
PWM Channels	Not Present	Inbuilt	Inbuilt

16x2 LCD Module

2014-11-27T17:05:00.000+05:30

16x2 LCD

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers, namely, Command and Data.

LCD (Liquid Crystal Display) screen is an electronic display module and find a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom characters (unlike in seven segments), animations and so on.

The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD. Click to learn more about internal structure of a LCD.

Pin Diagram:

Pin No

Function

Name

1

Ground (0V)

Ground

2

Supply voltage; 5V (4.7V – 5.3V)

Vcc

3

Contrast adjustment; through a variable resistor

V_EE

4

Selects command register when low; and data register when high

Register Select

5

Low to write to the register; High to read from the register

Read/write

6

Sends data to data pins when a high to low pulse is given

Enable

7

8-bit data pins

DB0

8

DB1

9

DB2

10

DB3

11

DB4

12

DB5

13

DB6

14

DB7

15

Backlight V_CC (5V)

Led+

16

Backlight Ground (0V)

Led-

The LCD works with voltage pulses only and that with precise timing and voltage levels. Hence special kinds of LCD drivers are developed to drive the LCD. Two or more of this kind of driver ICs together with the LCD screen forms LCD modules which are normally found in embedded systems.The LCD module makes a system stand-alone which can take input and display the corresponding output.

Xiaomi Mi 3 full specification and Buy now

2014-10-22T23:00:00.000+05:30

Xiaomi Mi 3

Buy now on Flipkart

Accelerate your life

The fastest Mi phone ever

A dragon in your pocket

Qualcomm Snapdragon 800 8274AB 2.3GHz processor, Adreno 330 450MHz GPU, 2GB LPDDR3 RAM, and eMMC 4.5 flash memory.

Experience your favourite games and apps at blazing speeds with the latest and most powerful processor from Qualcomm - 8274AB.

2GB LPDDR3 RAM

LPDDR3 is 50 percent faster than its predecessor

and consumes 20 percent less power.

Stunningly beautiful

5-inch IPS display. Full HD at 16:9.

See crisp details in 1080p HD video or rich textures in 3D game environments. Your photos look more vibrant in your hands now. Our full-screen, anti-glare coating gives you high screen readability wherever you go.

13MP camera with dual-LED flash

Take amazing photos in low light with a super-large Exmor sensor and an f/2.2 aperture. The built-in Phillips dual-LED flash quickly adds the perfect lighting to make your subjects beautiful. Never miss another photo opportunity again.

Power through your day

500 hours of standby time
50 hours of music playback
25 hours of talk time
21 hours of 3G Internet use

Lose the wires

Dual-band Wi-Fi (2.4Ghz/5Ghz) gives you the room to go wireless and still enjoy high speed Internet access. NFC (Near Field Communication) gives you the contactless freedom to augment your digital lifestyle.

Amazing from the inside out

Mi 3 is 8.1mm thin, 145 grams light, and houses an aluminum-magnesium alloy frame, coated with 3 layers of thermal graphite.

Make Android yours

We listen. The features in MIUI are based on the feedback we get from our 35 million users. We are constantly looking for new ways to make MIUI more useful, more secure, and more fun. We work around the clock (and drink much coffee) to fix bugs, and deliver new updates to your phone as quickly as possible.

Technical Specifications

Weight and dimensions

Chipset
CPU	Qualcomm Snapdragon 800 8274AB
CPU	XT 712
GPU	Adreno 330

Camera
Camera (back)	13 Megapixels
Aperture	f2.2
Wide-angle	28mm
Flash	dual-LED
Camera (front)	2 Megapixels
Sensor type	Stacked CMOS Both cameras (front and back) support 1080p HD video recording

* Mi 3 supports Mini SIM cards.

Connectivity
Cellular and wireless	Supports 3G(WCDMA) and 2G(GSM) networks
Frequencies	2G:GSM 850/900/1800/1900MHz 3G:WCDMA 850/900/1900/2100MHz
Data services	GPRS/EDGE/DC-HSPA+(42Mbps)
GPS	GPS + GLONASS, AGPS
Bluetooth	Bluetooth®4.0, Bluetooth HID
Wi-Fi	Wi-Fi Display，Wi-Fi Direct，5GHz Wi-Fi

OTG USB Yes

Battery
Capacity	3050mAh lithium-ion battery

Multimedia
Microphone	Supported
NFC	Supported
Haptic feedback	Supported

RAM
RAM	2GB RAM
Flash Memory	16 GB

Display
Display	5-inch Full HD 1080p LCD touch display
IPS	IPS Retina display manufactured by Sharp or LG
PPI	441
Resolution	1920x1080 FULL HD
Touch sensor	Supported

Video
Video Recording	1080p HD video recording
Others	Video stabilizer

Audio
Software	Dirac HD sound

Sensors
Gyroscope	Supported
Light sensor	Supported
Accelerometer	Supported
Proximity sensor	Supported
Electronic compass	Supported
Barometer	Supported

Operating System
Android	4.3 optimized with MIUI version 5

It is only Available on Flipkart.

Buy now on Flipkart

Water Sensor Circuit

2014-09-17T15:58:00.000+05:30

Water Sensor Circuit

This water sensor circuit is very sensitive to trigger and activate the audio visual alarm when wetness is sensed at its probes. This project is useful at homes to detect the water supply in the situations when the timing of water supply is not fixed. This circuit uses the 555 timer along with some sensor element which can detect moisture.

In this water sensor circuit based project, 555 timer works in astable mode. It is driven by the emitter current which is coming from BC548 transistor as this transistor has high gain. In astable mode IC 555 functions as an oscillator. So for 555 to work in full oscillator mode a high current is required so as to trigger it. As the probes sense the moisture on it, the transistor gets switched ON and small current starts flowing between the base and the emitter. When no moisture is detected i.e. in dry state it remains OFF.

Initially as the supply is switched ON, the voltage at output pin of 555 timer is 0V. At this stage transistor will not conduct as the emitter current is LOW. Pin8 i.e. Vcc of 555 timer is connected to the collector of the transistor. As the transistor is switched OFF there will be no supply to 555 timer. As the water is sensed at the probes, transistor gets into its saturation region and starts conducting. As a result 555 gets supply for its operation. Its operation starts very soon as it is in astable mode. Sound is produced because of output pulses at pin3 which drives the loud speaker.

An ON/OFF state switch is used to control the conduction. The probes should be made up of non reactive metal so that there will be no inductance or capacitance present. An alternative can also be there i.e. use of alternate copper wires. No base resistor is required in this circuit because the transistor is in switch mode. The impedance at the emitter or the oscillator circuit acts as current limit.

Vehicle Indicator circuit

2014-09-16T17:49:00.000+05:30

Vehicle Indicator circuit

The project illustrated below helps to find out nearby person or vehicle and make them visible to one another. It can be used in various applications for pedestrians, runners, bicyclists, motorcyclists, vehicles etc.

Most of the time during the night when the roads are badly lit the risk of accidents increases. Sometimes it happens that our vehicle breaks down and we need help. In such conditions this reflector can be used which automatically gets turned ON when it receives light from another vehicle passing nearby. The circuit is based on 555 timer IC and uses a NE555 version of it. The pin diagram of the IC is shown in the image

The reflector circuit consists of Light dependent resistor (LDR), timer IC (NE555), some bright LED’s and Transistor (BC549) which is used as buffer. In this project 555 timer is configured in oscillatory mode.

When ambient light is dim a potential drop occurs across the light dependent resistor (LDR) below the level set by VR1. Due to this the reset terminal (PIN4) of NE555 goes high to enable the oscillator.

In other words we can say that in the presence of light, the resistance at PIN4 of IC1 is very low. Hence no signal is passed to PIN4 of IC1 so the voltage at pin 4 becomes equal to zero. As a result of this low voltage the circuit remains OFF and in the darkness vice versa occurs so PIN4 of IC1 becomes high and we get the output.

this circuit can also be used as emergency night light, which puts on automatically.

Basic Computer Terms You Should Know Before Buying A PC

2014-08-10T17:59:00.001+05:30

Basic Computer Terms You Should Know Before Buying a PC

Have you decided to get rid of that old paperweight and buy yourself a new computer? Good for you but before you go running out to buy the latest and greatest machine, there are some basic computer terms you should know. We will run through each of these terms for you and what they mean.

The terminology used below is the same for PCs and Macs and for desktops and laptops. If you have any doubts about the machine you are buying. don’t buy it! Go and do some research online to see if you can do better
When you are looking to buy a computer you will hear basic computer terms like the following:

The Processor

This is the brain of your computer. It can also be referred to as the CPU. Processors come in many different varieties. Processor speed is termed as clock speed measured in gigahertz or GHz. more the value of GHZ the faster the computer.
I am now using a 3.06 GHz Intel^® dual core^TM i3 processor. Processors can also have dual or quad cores. This is essentially two or four processors in one respectively. The more cores the better but they will also be more expensive. We will also see terms like Core Duo, Core 2 Duo, i3, i5, and i7. It is important to know the differences between these options.
The Core Duo consists of two cores on one die but the Core 2 Duo is a more modern processor that is found in a lot of new PCs. the Core 2 Duo has two dies. Then the i3 processor is a recent release by Intel for new home machines. Then the i5 and i7 are used with quad core processors and higher end machines. The i7 is the top of this line and obviously the most expensive.
There are different brands of processors like Intel or AMD and different levels of processors like the Pentium 4 or the Atom. The Atom processor is a much slower processor used in notebooks.

The RAM

The RAM or memory is what your computer uses to store information while you are using the computer. I am using Transcend 4 GB DDR3 Ram .This can also be referred to as Random Access Memory. I personally would not buy a computer with less than 2 GB of RAM. Your RAM Bus speed will need to be identical to your FSB speed as to not create bottlenecks. In a pre-built system this is not something you need to worry about but if you are building your own system then you will want to get memory that matches the FSB speed divided by the number of cores that you have. For example if your system has a total FSB of 1600 and you have 4 cores (quad) then your RAM Bus speed should be 400 MHz.

Optical Drive

The optical drive in your computer should be able to read and write CDs and DVDs. If you have not purchased a computer in a while some of the newer options might seem strange to you. You can have any one of these or a combination of these formats: DVD-R, DVD+R, DVD-+R, DVD-/+RW, DVD-RAM, Blu-ray, HD-DVD. A CD holds 700 MB. A CD-R can read and write to a CD. A CDRW can read write and rewrite to a CD.
If you are getting a DVD burner you should try and get a drive that writes in all formats such as +R or -R. They will all play in your computer but some other hardware might require one of these formats. A DVD can hold About 4 GB of data. A DVD burner that allows you to burn a DL or dual layer will allow for double the capacity and can fit about 8 GB of data on it. A dual layer drive is required as well as dual layered media.
Then we see the newer formats like Blu-Ray and HD-DVD that allow you to burn and watch high definition videos or store even more data. A Blu-Ray disk can hold a whopping 25 GB in a single layer and 50 GB if the disk is dual layered. HD-DVD disks can hold up to 15 GB of data but I really do not see many systems or people using this format.

Wireless Network Card

If your computer has a wireless card you will be able to access the Internet without a wire connecting you to a router/modem. Wireless cards are rated by their speed.
The lowest speed starts from A and goes up through N. You will want to buy a computer with a 802.11G or 802.11N wireless connection. 802.11g can see speeds of up to 54 Mbit/s. And with 802.11n the newest iteration of wireless we can achieve 600 Mbit/s. I am using a 802.11n router personally but most of my equipment and peripherals use 802.11g. I find this to be fine for streaming video or audio and transferring files over my home network. But if you are constantly transferring huge files or folders you might want to jump right into the 802.11n game.

Network Card

Your computer should have an Ethernet port on it. This port will allow you to physically connect to the internet or your internal network by plugging it into your router / modem.
Normally any machine you will buy now has a Gigabit connection. Gigabit is represented as 100/1000 and there are also 10/100 connections. That number is how many megabits you can transfer per second.

Operating System

This is the software that makes your computer go. You can buy a computer with the Windows 7 or 8 any flavor of Ubuntu Linux as well. Windows 8 is good for touch screen pc. You can choose windows 7. Different versions are home premium, home basic, professional, Ultimate. I am using windows 7 ultimate.
You can also buy a computer without an operating system to install it yourself. This is the key part of your system as well as normally the most expensive. But, if you choose Ubuntu or another flavor of Linux then your operating system is free.

Hard Drive

This is where you will store all your files whether it be music, movies or word documents. You will need a hard drive to store them on.
Seagate and WD (Western Digitals) are most famous companies and are good.
Hard drives are rated by size and speed. These are available in two different speed, that is 7200RPM and 5400 RPM. More the speed of HDD you can access fast.
If you need more space you should get a bigger drive or you can buy a portable USB hard drive to attach to your computer. Normally 500GB is used maximum 1TB is used..

Video Card

This is the part of your computer that allows you to show what you are doing. Without a video card you would not be able to see what you are doing on your monitor. Normally it is already built-in in mother board.
Different video cards have different abilities like the option to use multiple monitors, have a HDMI output or even the ability to watch HD movies on your computer. This has never been important to me and I always take whatever is available. Some examples of good video card brands are MSI, XFX, Asus, Gigabyte.
Your video card does have to connect to your monitor so make sure they have a VGA, DVI or HDMI port in common.
There are also computer components like the monitor, keyboard and mouse but we’re pretty sure that you’re familiar with those basic computer terms.
Now, you have a basic knowledge of what you are looking for start shopping around. The best deals are found online.

Monitor

There are three types of monitor namely CRT, LCD and LED. But CRT(cathode ray tube) monitors are disappearing in markets. LCD and LED are all same but only change in backlight. In LCD Florescent lamps are used, but in LED it is done by LED lamps. LED monitor is most preferable because it has more moving angle.

The next thing to select is aspect ratio. Monitors are available in 16:9 and 4:3 . The old monitors have aspect ratio 4:3. But the HD videos are in 16:9 ratio. So 16:9 ratio is preferable.

battery charger circuit & battery level indicator with low battery recharge alarm

2014-08-10T17:59:00.000+05:30

battery charger circuit & battery level indicator with low battery recharge alarm

This is a simple circuit of 12V rechargeable smart battery charger circuit. You can use this best battery charger circuit as car battery chargers, Inverter battery charger, Emergency battery charger etc. Automatic indicator alarm circuit is also comes along with this battery charger schematic. The main advantage of this indicator is that a buzzer informs us when the battery needs recharge. This circuit schematic definitely helps for your daily life battery charging applications.

Circuit diagram of battery charger

Components required

Transformer (230V to 15V or 110V t0 15V)
Bridge rectifier (1N4007 x 4)
Capacitor (470µF, 50V)
Voltage regulator IC 7815
12V rechargeable battery
Diode (1N4148)
LED Zener diode 9V
Transistor (BC547 x 2)
Resistors (10kΩ, 1.5kΩ, 100kΩ Each ¼ Watt)
Buzzer (12V)

Working of battery charger circuit

The charging circuit is build around voltage regulator IC 7815 and two transistors BC 548.

The main supply 230V or 110V is step down using a step down transformer, and then it is rectifiered and filtered out.

That DC voltage is fed to the voltage regulator IC 7815; the output will be regulated 15V.

12 volt rechargeable battery is connected at the output of voltage regulator and it charges when main power is available.

This circuit indicates the charging status that is the LED1 is glows when the battery charged (Above 10.5V).

When battery voltage goes below a particular value LED1 stops glowing and the buzzer produces sound indicating that the battery has been discharged and it needs recharge.

What fevikwik made of?

2014-08-10T17:58:00.000+05:30

What fevikwik made of?

Cyanoacrylate

Cyanoacrylate is the generic name for a family of strong fast-acting adhesives with industrial, medical and household uses. Cyanoacrylate adhesives have a short shelf life if not used, about one year from manufacture if unopened, one month once opened. They have some minor toxicity.

Cyanoacrylates include methyl 2-cyanoacrylate, ethyl-2-cyanoacrylate (commonly sold under trade names such as "Super Glue", "fevikwik" and "Krazy Glue"), n-butyl cyanoacrylate and 2-octyl cyanoacrylate (used in medical, veterinary and first aid applications). Octyl cyanoacrylate was developed to address toxicity concerns and to reduce skin irritation and allergic response. Cyanoacrylate adhesives are sometimes known generically as instant glues or superglues (although "Super Glue" is a trade name). The abbreviation "CA" is commonly used for industrial grades.

Development

The original cyanoacrylates (the chemical name for the glue) were discovered in 1942 in a search for materials to make clear plastic gun sights during World War II, when a team of scientists headed by Harry Wesley Coover Jr. stumbled upon a formulation that stuck to everything that it came in contact with; it was rejected for the application. In 1951 cyanoacrylates were rediscovered by Eastman Kodak researchers Harry Coover and Fred Joyner, who recognized their true commercial potential; "Eastman #910" (later "Eastman 910") was the first cyanoacrylate adhesive to be sold, in 1958.

During the 1960s Eastman Kodak sold cyanoacrylate to Loctite, which in turn repackaged and distributed it under a different brand name "Loctite Quick Set 404". In 1971 Loctite developed its own manufacturing technology and introduced its own line of cyanoacrylate, called "Super Bonder". Loctite quickly gained market share, and by the late 1970s it was believed to have exceeded Eastman Kodak's share in the North American industrial cyanoacrylate market. National Starch and Chemical Company purchased Eastman Kodak’s cyanoacrylate business and combined it with several acquisitions made throughout the 1970s forming Permabond. Other manufacturers of cyanoacrylate include LePage (a Canadian company acquired by Henkel in 1996), the Permabond Division of National Starch and Chemical, Inc., which was a subsidiary of Unilever. Together, Loctite, Eastman and Permabond accounted for approximately 75% of the industrial cyanoacrylate market. As of 2013 Permabond continued to manufacture the original 910 formula.

Properties

In its liquid form, cyanoacrylate consists of monomers of cyanoacrylate molecules. Methyl-2-cyanoacrylate (CH₂=C(CN)COOCH₃ or C₅H₅NO₂) has a molecular weight equal to 111.1, a flashpoint of 79 °C, and a density of 1.1 g/ml. Ethyl 2-cyanoacrylate (C₆H₇NO₂) has a molecular weight equal to 125 and a flashpoint of >75 °C. To facilitate easy handling, a cyanoacrylate adhesive is frequently formulated with an ingredient such as fumed silica to make it more viscous or gel-like. More recently, formulations are available with additives to increase shear strength, creating a more impact resistant bond. Such additives may include rubber, as in Loctite's Ultra Gel, or others which are not specified.

In general, cyanoacrylate is an acrylic resin that rapidly polymerises in the presence of water (specifically hydroxide ions), forming long, strong chains, joining the bonded surfaces together. Because the presence of moisture causes the glue to set, exposure to normal levels of humidity in the air causes a thin skin to start to form within seconds, which very greatly slows the reaction. Because of this cyanoacrylate is applied thinly, to ensure that the reaction proceeds rapidly and a strong bond is formed within a reasonable time.

The reaction with moisture can cause a container of glue which has been opened and resealed to become unusable more quickly than if never opened. To minimise this reduction in shelf life cyanoacrylate, once opened, can be stored in an airtight container with a package of silica gel desiccant. Another technique is to insert a hypodermic needle into the opening of a tube. After using the glue, residual glue soon clogs the needle, keeping moisture out. The clog is removed by heating the needle (e.g., by a lighter) before use.

Uses

Cyanoacrylates are mainly used as adhesives. They require some care and knowledge for effective use: they do not bond some materials; their shelf life at room temperature is about 12 months unopened and one month once opened; they do not fill spaces, unlike epoxies, and a very thin layer bonds more effectively than a thicker one that does not cure properly; they bond many substances, including human skin and tissues, almost instantly and can cause harm to people.

Cyanoacrylate glue has a low shearing strength, which has led to its use as a temporary adhesive in cases where the piece needs to be sheared off later. Common examples include mounting a workpiece to a sacrificial glue block on a lathe, and tightening pins and bolts.

Cyanoacrylates are used to assemble prototype electronics (see wire wrap), flying model aircraft, and as retention dressings for nuts and bolts. Their effectiveness in bonding metal and general versatility have made them popular among modeling and miniatures hobbyists. They are used to re-harden the boxes and shanks of ballerinas' pointe shoes.

Cyanoacrylate glue's ability to resist water has made it popular with marine aquarium hobbyists for fragging corals. The cut branches of hard corals such as Acropora can be glued to a piece of live rock (harvested reef coral) or Milliput (epoxy putty) to allow the new frag to grow out. It is actually safe to use directly in the tank, unlike silicone, which must be cured to be safe. However, as a class of adhesives, traditional cyanoacrylates are classified as having "weak" resistance to both moisture and heat although the inclusion of phthalic anhydride reportedly counteracts both of these characteristics.

Most standard cyanoacrylate adhesives do not bond well with smooth glass, although they can be used as a quick, temporary bond prior to application of an epoxy or cyanoacrylate specifically formulated for use on glass. A mechanical adhesive bond may be formed around glass fibre mat or tissue to reinforce joints or to fabricate small parts.

Cyanoacrylate is used in the cosmetology/beauty industry as a "nail glue" for some artificial nail enhancements such as nail tips and nail wraps, and is sometimes mistaken for eye drops causing accidental injury.

Safety issues

Toxicity

The fumes from CA are a vaporized form of the cyanoacrylate monomer that irritate sensitive membranes in the eyes, nose, and throat. They are immediately polymerized by the moisture in the membranes and become inert. These risks can be minimized by using CA in well ventilated areas. About 5% of the population can become sensitized to CA fumes after repeated exposure, resulting in flu-like symptoms. It may also act as a skin irritant and may cause an allergic skin reaction. The ACGIH assign a Threshold Limit Value exposure limit of 200 parts per billion. On rare occasions, inhalation may trigger asthma. There is no singular measurement of toxicity for all cyanoacrylate adhesives as there is a wide variety of adhesives that contain various cyanoacrylate formulations.

The United States National Toxicology Program and the United Kingdom Health and Safety Executive have concluded that the use of ethyl cyanoacrylate is safe and that additional study is unnecessary. 2-octyl cyanoacrylate degrades much more slowly due to its longer organic backbone that slows the degradation of the adhesive enough to remain below the threshold of tissue toxicity. Due to the toxicity issues of ethyl cyanoacrylate, the use of 2-octyl cyanoacrylate for sutures is preferred.

Reaction with cotton

Applying cyanoacrylate to some materials made of cotton or wool (such as cotton swabs, cotton balls, and certain yarns or fabrics) results in a powerful, rapid exothermic reaction. The heat released may cause serious burns, ignite the cotton product, or release irritating white smoke. Material Safety Data Sheets for cyanoacrylate instruct users not to wear cotton or wool clothing, especially cotton gloves, when applying or handling cyanoacrylates.

Solvents and debonders

Acetone, commonly found in nail polish remover, is a widely available solvent capable of softening cured cyanoacrylate. Other solvents include nitromethane, dimethyl sulfoxide, and methylene chloride. gamma-Butyrolactone may also be used to remove cured cyanoacrylate. Commercial debonders are also available.

Shelf life

Cyanoacrylate adhesives have a short shelf life. Date-stamped containers help to ensure that the adhesive is still viable. One manufacturer supplies the following information and advice: when kept unopened in a cool, dry location such as a refrigerator at a temperature of about 55°F (13°C), the shelf life of cyanoacrylate will be extended from about one year from manufacture to at least 15 months. If the adhesive is to be used within six months, it is not necessary to refrigerate it. Cyanoacrylates are moisture-sensitive, and moving from a cool to a hot location will create condensation; after removing from the refrigerator, it is best to let the adhesive reach room temperature before opening. After opening cyanoacrylate should be used within thirty days. Open containers should not be refrigerated. Another manufacturer says that the maximum shelf life of 12 months is obtained for some of their cyanoacrylates if the original containers are stored at 35 to 40 °F (2 to 4 °C). User forums and some manufacturers say that an almost unlimited shelf life is attainable by storing unopened at −20 °C (−4 °F), the typical temperature of a domestic freezer, and allowing to reach room temperature before use. (Rechilling an opened container is not advisable as it will cause moisture from the air to condense in the container, causing deterioration.)

As cyanoacrylates age they polymerize, become thicker, and cure more slowly. They can be thinned with a cyanoacrylate of the same chemical composition with lower viscosity.

How Intel makes integrated circuit chips?

2014-08-10T17:57:00.000+05:30

How Intel makes integrated circuit chips

From sand to circuits

The Intel® Core™2 Duo processor with Intel 45nm High-k metal gate silicon technology

“ The implementation of High-k and metal materials marks the biggest change in transistor technology since the introduction of polysilicon gate MOS transistors in the late 1960s.”

Gordon Moore, Intel Co-Founder

Revolutionary

The task of making chips like these—the most complex devices ever manufactured—is no

small feat. A sophisticated chip, such as a microprocessor, can contain hundreds of millions

or even billions of transistors interconnected by fine wires made of copper. These transistors

act as switches, either preventing or allowing electrical current to pass through. A positive

charge fed to a transistor’s gate attracts electrons. This gate creates a channel between the

transistor’s source and drain through which electrical current flows, creating an “on” state.

A negative charge at the gate prevents the current from being able to flow through,

creating an “off” state for the transistor.

Intel uses its advanced manufacturing technology to build several hundred trillion transistors

every day. Intel’s breakthrough 45-nanometer (nm) High-k silicon technology enables the

production of transistors that are so small that 2 million of them would fit into the period

at the end of this sentence.

Intel’s success at reducing transistor size and maximizing performance results in advanced

processor technology that helps drive other innovations in almost all industries. Today, silicon

chips are everywhere—powering the Internet, enabling a revolution in mobile computing,

automating factories, enhancing cell phones, and enriching home entertainment. Silicon is

at the heart of an ever expanding, increasingly connected digital world.

Explore this brochure to learn how Intel makes silicon chips. If you are unfamiliar with a

technical term, see the “Terminology” section at the end of the brochure. It defines the

words that are italicized in the text.

Design

Intel creates a logic description of a new chip.

Simulators take the register transfer level (RTL) code

(shown in the background of this image) to verify the

accuracy of the specification before fabrication begins.

Silicon chip manufacturing starts with a design, or a blueprint.

Intel considers many factors. What type of chip is needed and why?

How many transistors can be built on the chip?

What is the optimal chip size? What technology will be available to create the chip? When does

the chip need to be ready? Where will it be manufactured and tested?

To answer these questions, Intel teams work with customers, software companies, and Intel’s

marketing, manufacturing, and testing staff. Intel design teams take this input and begin the

monumental task of defining a chip’s features and design.

When the specifications for the chip are ready, Intel creates a logic design, an abstract

representation of the millions of transistors and interconnections that control the flow of

electricity through a chip. After this phase is complete, designers create physical representations

of each layer of the chip and its transistors. They then create stencil-like patterns, or masks,

for each layer of the chip. Masks are used with ultraviolet light during a fabrication process

called photolithography.

To complete the design, testing, and simulation of a chip, Intel uses sophisticated computer-aided

design (CAD) tools. CAD helps designers create very complex designs that meet functional and

performance goals.

After extensive modeling, simulation, and verification, the chip is ready for fabrication. It can

take hundreds of engineers working full time for more than two years to design, test, and ready

a new chip design for fabrication.

Moore’s Law

In 1965, Gordon Moore predicted that the number of transistors on a piece of silicon would double every year—an insight later dubbed “Moore’s Law.” Intended as a rule of thumb, it has become the guiding principle for the industry to deliver ever more powerful semiconductor chips at proportionate decreases in cost. In 1975, Moore updated his prediction that the number of transistors that the industry would be able to place on a computer chip would double every couple of years. The original Moore’s Law graph is shown here.

Moore’s Law has been amazingly accurate over
time. In 1971, the Intel 4004 processor held
2,300 transistors. In 2008, the Intel® Core™2
Duo processor holds 410 million transistors.
A dramatic reduction in cost has also occurred.
In 1965, a single transistor cost more than
one dollar. By 1975, the cost was reduced to
one cent, and today Intel can manufacture
transistors that sell for less than 1/10,000 of a
cent each. Intel’s 45nm High-k silicon technology
ensures that Intel will continue to deliver
Moore’s Law into the next decade.

Fabrication

The process of making chips is called fabrication. The factories where
chips are made are called fabrication facilities, or fabs. Intel fabs are
among the most technically advanced manufacturing facilities in the
world. Within these sophisticated fabs, Intel makes chips in a special
area called a cleanroom.

Because particles of dust can ruin the complex circuitry on a chip, cleanroom air must be ultra-clean.
Purified air is constantly re-circulated, entering through the ceiling and exiting through floor tiles.
Technicians put on a special suit, commonly called a bunny suit, before they enter a cleanroom.
This helps keep contaminants such as lint and hair off the wafers. In a cleanroom, a cubic foot of
air contains less than one particle measuring about 0.5 micron (millionth of a meter) across. That’s
thousands of times cleaner than a hospital operating room.

Automation also plays a critical role in a fab. Batches of wafers are kept clean and processed quickly
and efficiently by traveling through the fab inside front-opening unified pods (FOUPs) on an overhead
monorail. Each FOUP receives a barcode tag that identifies the recipe that will be used to make
the chips inside. This labeling ensures the correct processing at each step of fabrication. Each FOUP
contains up to 25 wafers and weighs more than 25 pounds. Production automation machinery
allows for this FOUP weight, which is too heavy to be handled manually by technicians.

1 Orange FOUPs carry 300mm wafers in an automated fab.

2 Highly trained technicians monitor each phase of chip fabrication.

3 Purified air enters from the ceiling and exits through perforated floor tiles.

4 A technician holds a 300mm wafer.

Silicon, the principal
ingredient in beach
sand, is a natural
semiconductor and
the most common
element on earth
after oxygen.

The “recipe” for fabricating a chip varies depending on the chip’s proposed use. Intel uses a variety of
ingredients and performs as many as 300 steps with chemicals, gas, or light to complete fabrication.
A sandy start It all starts with silicon, the principal ingredient in common beach sand. Intel builds chips in batches on wafers made of ultra-pure silicon. Silicon is a semiconductor. This means that unlike insulators such as glass (which always resist the passage of electrons) or conductors such as copper (which generally let electrons pass through), silicon can be altered to be a conductor or an insulator. Silicon is a good choice for making wafers because it is abundant, its oxide is a good insulator, and the industry has decades of experience working with it.

To make wafers, silicon is chemically processed so that it becomes 99.9999% pure. The purified silicon is
melted and grown into long, cylindrical ingots. The ingots are then sliced into thin wafers that are polished
until they have flawless, mirror-smooth surfaces. When Intel first started making chips, the company
used 2-inch-diameter wafers. Now the company uses primarily 12-inch, or 300-millimeter (mm) wafers;
larger wafers are more difficult to process, but the result is lower cost per chip.
Layer by layer
Intel uses a photolithographic “printing” process to build a chip layer by layer. Many layers are deposited
across the wafer and then removed in small areas to create transistors and interconnects. Together,
they will form the active (“on/off”) part of the chip’s circuitry plus the connections between them, in a
three-dimensional structure. The process is performed dozens of times on each wafer, with hundreds
or thousands of chips placed grid-like on a wafer and processed simultaneously.

Process

1. Start with a partially processed die on a silicon
wafer. A chip is often referred to as die until final packaging
has been completed.

2. Deposit oxide layer. A thin film of oxide is an electrical
insulator. Like the insulator surrounding household wires,
it is a key component of electronic circuits. Intel “grows”
this layer of oxide on top of the wafer in a furnace at very
high temperatures in the presence of oxygen.

3. Coat with photoresist. A light-sensitive substance called
photoresist prepares the wafer for the removal of sections
of the oxide to create a specific oxide pattern. Photoresist is
sensitive to ultraviolet light, yet it is also resistant to certain
etching chemicals that will be applied later.

4. Position mask and flash ultraviolet light. Masks—
pieces of glass with transparent and opaque regions—are
a result of the design phase and define the circuit pattern
on each layer of a chip. A sophisticated machine called a
stepper aligns the mask to the wafer. The stepper “steps”
across the wafer, stopping briefly at incremental locations to
flash ultraviolet light through the transparent regions of the
mask. This process is called photolithography. The portions
of the photoresist that are exposed to light become soluble.

5. Rinse with solvent. A solvent removes the exposed
portions of photoresist, revealing part of the oxide
layer underneath.
6. Etch with acid. Using an acid in a process called etching,
the exposed oxide is removed. Oxide protected by the
mask remains in place.

7. Remove remaining photoresist. Finally, the
remaining photoresist is removed, leaving the desired
pattern of oxide on the silicon wafer. A new oxide
layer is complete.

Building circuits to form a computer chip is extremely precise and complex. It requires dozens of layers of various materials in specific patterns to simultaneously produce hundreds or thousands of die on each 300mm wafer. The following illustration takes a closer look
at the process of adding one layer—a single patterned oxide film.

Performing More Fabrication Steps

Laying down an oxide layer is just one part of the fabrication
process. Other steps include the following.
Adding more layers
Additional materials such as polysilicon, which conducts
electricity, are deposited on the wafer through further
film deposition, masking, and etching steps. Each layer of
material has a unique pattern.

Doping

The doping operation bombards the exposed areas of
the silicon wafer with various chemical impurities, altering
the way the silicon in these areas conducts electricity.
Doping is what turns silicon into silicon transistors, enabling
the switching between the two states, on and off, that
represent binary 1s and 0s, which provide the basis
for representing information in a computer.

Metallization

Multiple layers of metal are applied to form the electrical
connections between the transistors. Intel uses eight or
more patterned layers of copper because of its low resistance
and because it can be cost-effectively integrated into the
manufacturing process. Interconnects between layers, called
contacts, are made of tungsten. The specific patterns of
these metals are also formed using photolithography, as
described previously.

Completing the wafer

A completed wafer contains millions or even billions of
transistors connected by a multi-layer maze of metal
“wires.” Finally, the wafer is coated with a passivation
layer to help protect it from contamination and increase
its electrical stability.

Testing and Packaging

After creating layers on the wafers, Intel performs wafer sort, and a computer completes a series of tests to ensure
that chip circuits meet specifications to perform as designed.
Intel sends the approved wafers to an Intel assembly facility, where a precision saw
separates each wafer into individual rectangular chips, called die. Each functioning
die is assembled into a package that, in addition to protecting the die, delivers critical
power and electrical connections from the main circuit board on a computer. It is
this final “package” that is placed directly on a computer circuit board or in other
devices such as cell phones and personal digital assistants (PDAs).
As processor technologies advance, the demands on packaging to support and
optimize the technologies increase. Because Intel makes chips that have many
different applications, the company uses a variety of packaging technologies.

High-performance packages

Flip-chip packaging. Flip-chip packaging is an example of one of the advanced
packages that Intel uses. To package the die, Intel begins by attaching tiny metal
bumps on the die surface to the supporting base, or substrate of the package,
completing an electrical connection from the chip to the package. This method is
called “flip chip” because the silicon die are “flipped” to their front side for attachment,
compared to other types of packaging that attach to the back of the die. Intel uses
an organic or polymer substrate to enable higher performance copper electrical
interconnections from the die to the circuit board. A compliant material is then added
between the substrate and the die to manage mechanical stress. In the last step,
Intel attaches a structure called a heat spreader to help disperse the heat generated
by the chip during normal use.

Wire bond for stacked-chip packaging. Stacked-chip packaging technologies
result in packages that are only slightly larger than the multiple silicon die that they
contain. Intel stacks multiple memory and logic die in a single package to increase
performance and minimize the use of space, which are critical in today’s small handheld
devices. When attaching the die, Intel uses a special material that is optimized for
mechanical, thermal, and electrical performance to “glue” the first die to the substrate.
The other die are then stacked and “glued” to each other to create a combination of
chips that meet product performance goals.
After the die are attached, sophisticated tools bond extremely fine wires from each
die to the substrate. This process, called wire bonding, is repeated for each die included
in the stack until all die are electrically connected to the same package. The die are
then encapsulated with a molding process and a protective coating that flows into
the narrow spaces between the die and the package. Lastly, Intel attaches specialized
alloy “balls” to the bottom of the package to electrically connect the package to the
circuit board.

One more check

Intel performs reliability and electrical “tests” on each completed unit. The company
verifies that the chips are functional and perform at their designed speed across a
variety of temperatures. Because chips may end up in items ranging from automobile
engines to spacecraft and laptops, they must be able to withstand many different
environmental stresses. Chips are also tested for long-term reliability to ensure that
they will continue to perform as specified. Upon approval, chips are electrically coded,
visually inspected, and packaged in protective materials for shipment to Intel customers.

Innovation

Intel’s processor technologies offer exciting advancements, including

state-of-the-art chips with multiple cores, or “brains.”

These brains enable the efficient execution of parallel tasks, such as when a computer simultaneously

performs word processing, plays music, prints a file, and checks for viruses. Multi-core processor architectures significantly improve performance while increasing energy efficiency, which is an important consideration in today’s high-performance products.

Intel has a long history of translating technology leaps into tangible benefits. It’s not just about making technology faster, smarter, and cheaper—it’s about using that technology to make life better and our experiences richer.

Undisputed Leadership

Unwavering commitment to moving technology forward

Terminology

Intel 45nm High-k metal gate silicon technology: One of

the biggest advances in fundamental transistor design. Intel’s

innovative combination of metal gates and High-k gate dielectrics

reduces electrical current leakage as transistors get ever smaller.

Binary: Having two parts. The binary number system that

computers use is composed of the digits 0 and 1.

Channel: The region under the gate of a transistor where current

flows when the transistor is in the “on” state.

Chip: A tiny, thin square or rectangle that contains integrated

electronic circuitry. Die are built in batches on wafers of silicon.

A chip is a packaged die. See also “Microprocessor.”

Circuit: A network of transistors interconnected by wires in a

specific configuration to perform a function.

Cleanroom: The ultra-clean room where chips are fabricated.

The air in a cleanroom is thousands of times cleaner than that

in a typical hospital operating room.

Computer-aided design (CAD): Sophisticated computerized

workstations and software that Intel uses to design integrated

circuits.

Die: Alternate name for a chip, usually before it is packaged.

Remote Tester Circuit

2014-06-18T14:21:00.001+05:30

Remote Tester Circuit

Today we are controlling many appliances with the help of remote like AC, TV or music system. It often happen that remote stops working due to any reason (low battery or any button of remote becomes faulty). Therefore here is the remote tester circuit to test your remote to identify that appliance (TV, AC etc) has problem or your remote is not responding. Advantage of circuit-

1. Based on single sensor.

2. Circuit consumes very less power.

3. Almost every remote can be tested with the help of this circuit as operating frequency of sensor is 38 KHz.

4. High immunity against ambient light.

5. With little modification in the circuit you can use it to control your home appliances with remote.

This remote tester circuit is based on infrared sensor IC TSOP1738. TSOP1738 contains photo detector and preamplifier both in one package. It is a three terminal device. Pin1 is used as ground pin. Pin 2 is for power supply and pin 3 is used for output. Pin diagram of TSOP1738 is shown below. Take care while connecting the TSOP pins as wrong connections may lead to damage of sensor. Following figure shows the pin diagram of TSOP1738.

Assemble the circuit as shown in circuit diagram and apply power supply. When power supply is given LED connected at the output starts blinking. When IR waves from remote fall on the sensor, its output changes to low state. This will turn ON the transistor connected at the output and LED will blink according to the button press on the remote. If this phenomenon happens, it means your remote is working fine. Here R2 and D1 are used to limit the current into the sensor. Do not supply more than 5V directly to pin 2 of TSOP1738 else it will destroy the sensor.

Cell Phone Controlled Home appliances

2014-06-17T22:35:00.001+05:30

Cell Phone Controlled Home appliances

Many of us face problem when we out of our home like if we want to on the motor, so that when we reach home water will be filled in over head tank or we want to on other appliances like light fan etc.

Hence to solve this problem we have describe a simple circuit which will on your device or appliances remotely and it will become off automatically after preset time interval.

Many circuits have been developed so far to solve this problem but main advantage of this circuit is uses readily available components and this circuit is not expensive as well because this circuit is made using without microcontroller.

This circuit is based on two IC's namely MT8870 which is DTMF decoder IC and another is NE555 timer which is wired as monostable multivibrator with few more components like crystal, relay, resistors and capacitors.

How to operate a device remotely

In this circuit for operating a device we will require two cell phone, one will be with us from which we will call on the other cell phone which is connected to device. And other cell phone will be connected to the device in auto answer mode. For operating the device call on the cell phone which is connected to the device as this cell phone is in auto answer mode it will pick up the call automatically . When ring stop dial number 7 from the keypad of the mobile from which you are calling. Now the device connected to it with the relay start operating and will become off automatically after certain time period.

Working of circuit

Connect the cell phone with the head phone or ear phone properly at mobile phone audio jack. Now when you call on the mobile connected with device at the receiving end DTMF decoder IC will provide a high pulse at pin 15 after detecting the valid tone pair. This will trigger the pin 2 of IC2 and its output will go from high to low. This in turn make the output pin 3 of IC2 high and the transistor T2 connected to it start conducting because of this relay energise and device become on. The time period for which device remain on can be adjusted with the help of variable resistor VR1 and capacitor C4. By increasing or decreasing the value of variable resistor and capacitor time period can be increased or decreased. This can be calculated by the below formula-

Time period = 1.1*VR1*C4 in seconds

In this circuit transistor T1 will only conduct when all the outputs pin 11, pin12, pin13 and pin15 will become high simultaneously with the help of diode D1 to D5. This can only be done by pressing the number 7 through DTMF decoder. The DTMF signal send from the dialler mobile end is decoded by the DTMF decoder and its respective BCD value appear at the output on pin 11, pin12, pin13. That's why to on the device we are using number 7.

Relay

2014-06-17T12:49:00.000+05:30

Relay

Relay is an electromagnetic device which is used to isolate two circuits electrically and connect them magnetically. They are very useful devices and allow one circuit to switch another one while they are completely separate. They are often used to interface an electronic circuit (working at a low voltage) to an electrical circuit which works at very high voltage. For example, a relay can make a 5V DC battery circuit to switch a 230V AC mains circuit. Thus a small sensor circuit can drive, say, a fan or an electric bulb.
A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

Basic design and operation

A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contact(s) either makes or breaks (depending upon construction) a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing.
When the coil is energized with direct current, a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to semiconductor circuit components. Some automotive relays include a diode inside the relay case.

Alternatively, a contact protection network consisting of a capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil is designed to be energized with alternating current (AC), a small copper "shading ring" can be crimped to the end of the solenoid, creating a small out-of-phase current which increases the minimum pull on the armature during the AC cycle.

A solid-state relay uses a thyristor or other solid-state switching device, activated by the control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-emitting diode (LED) coupled with a photo transistor) can be used to isolate control and controlled circuits.

Types

Latching relay

A latching relay has two relaxed states (bistable). These are also called "impulse", "keep", or "stay" relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remanent core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that one coil consumes power only for an instant, while it is being switched, and the relay contacts retain this setting across a power outage. A remanent core latching relay requires a current pulse of opposite polarity to make it change state.

A stepping relay is a specialized kind of multi-way latching relay designed for early automatic telephone exchanges
.
An earth leakage circuit breaker includes a specialized latching relay.
Very early computers often stored bits in a magnetically latching relay, such as ferreed or the later memreed in the 1ESS switch.

Some early computers used ordinary relays as a kind of latch—they store bits in ordinary wire spring relays or reed relays by feeding an output wire back as an input, resulting in a feedback loop or sequential circuit. Such an electrically-latching relay requires continuous power to maintain state, unlike magnetically latching relays or mechanically racheting relays.

In computer memories, latching relays and other relays were replaced by delay line memory, which in turn was replaced by a series of ever-faster and ever-smaller memory technologies.

Reed relay

A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas-filled glass tube which protects the contacts against atmospheric corrosion; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid or an external magnet.

Reed relays can switch faster than larger relays and require very little power from the control circuit. However, they have relatively low switching current and voltage ratings. Though rare, the reeds can become magnetized over time, which makes them stick 'on' even when no current is present; changing the orientation of the reeds with respect to the solenoid's magnetic field can resolve this problem.
Sealed contacts with mercury-wetted contacts have longer operating lives and less contact chatter than any other kind of relay.

Mercury-wetted relay

A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted with mercury. Such relays are used to switch low-voltage signals (one volt or less) where the mercury reduces the contact resistance and associated voltage drop, for low-current signals where surface contamination may make for a poor contact, or for high-speed applications where the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive and must be mounted vertically to work properly. Because of the toxicity and expense of liquid mercury, these relays are now rarely used.

Mercury relay

A mercury relay is a relay that uses mercury as the switching element. They are used where contact erosion would be a problem for conventional relay contacts. Owing to environmental considerations about significant amount of mercury used and modern alternatives, they are now comparatively uncommon.

Polarized relay

A polarized relay places the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion. The poles were on screws, so a technician could first adjust them for maximum sensitivity and then apply a bias spring to set the critical current that would operate the relay.

Machine tool relay

A machine tool relay is a type standardized for industrial control of machine tools, transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally-open to normally-closed status, easily replaceable coils, and a form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications.

A relay allows circuits to be switched by electrical equipment: for example, a timer circuit with a relay could switch power at a preset time. For many years relays were the standard method of controlling industrial electronic systems. A number of relays could be used together to carry out complex functions (relay logic). The principle of relay logic is based on relays which energize and de-energize associated contacts. Relay logic is the predecessor of ladder logic, which is commonly used in programmable logic controllers.

Ratchet relay

This is again a clapper type relay which does not need continuous current through its coil to retain its operation. A ratchet holds the contacts closed after the coil is momentarily energized. A second impulse, in the same or a separate coil, releases the contacts.

Coaxial relay

Where radio transmitters and receivers share a common antenna, often a coaxial relay is used as a TR (transmit-receive) relay, which switches the antenna from the receiver to the transmitter. This protects the receiver from the high power of the transmitter. Such relays are often used in transceivers which combine transmitter and receiver in one unit. The relay contacts are designed not to reflect any radio frequency power back toward the source, and to provide very high isolation between receiver and transmitter terminals. The characteristic impedance of the relay is matched to the transmission line impedance of the system, for example, 50 ohms.

Contactor

A contactor is a heavy-duty relay used for switching electric motors and lighting loads, but contactors are not generally called relays. Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver. The unavoidable arcing causes the contacts to oxidize; however, silver oxide is still a good conductor.

Contactors with overload protection devices are often used to start motors. Contactors can make loud sounds when they operate, so they may be unfit for use where noise is a chief concern.

A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit.

Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amperes to thousands of amperes and 24 V DC to many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side.

Solid-state relay

A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. Every solid-state device has a small voltage drop across it. This voltage drop limits the amount of current a given SSR can handle. The minimum voltage drop for such a relay is a function of the material used to make the device. Solid-state relays rated to handle as much as 1,200 amperes have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients and in general may be susceptible to damage by extreme cosmic ray and EMP episodes.

Solid state contactor relay

A solid state contactor is a heavy-duty solid state relay, including the necessary heat sink, used where frequent on/off cycles are required, such as with electric heaters, small electric motors, and lighting loads. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls.

Buchholz relay

A Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled transformers, which will alarm on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil.

Forced-guided contacts relay

A forced-guided contacts relay has relay contacts that are mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of forced-guided contacts is to enable the safety circuit to check the status of the relay. Forced-guided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", "mechanically-linked contacts", or "safety relays".

Overload protection relay

Electric motors need overcurrent protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings. The overload sensing devices are a form of heat operated relay where a coil heats a bimetallic strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized.

This thermal protection operates relatively slowly allowing the motor to draw higher starting currents before the protection relay will trip. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided.

The other common overload protection system uses an electromagnet coil in series with the motor circuit that directly operates contacts. This is similar to a control relay but requires a rather high fault current to operate the contacts. To prevent short over current spikes from causing nuisance triggering the armature movement is damped with a dashpot. The thermal and magnetic overload detections are typically used together in a motor protection relay.

Electronic overload protection relays measure motor current and can estimate motor winding temperature using a "thermal model" of the motor armature system that can be set to provide more accurate motor protection. Some motor protection relays include temperature detector inputs for direct measurement from a thermocouple or resistance thermometer sensor embedded in the winding.

Vacuum relays

A sensitive relay having its contacts mounted in a highly evacuated glass housing, to permit handling radio-frequency voltages as high as 20,000 volts without flashover between contacts even though contact spacing is but a few hundredths of an inch when open.

Derating factors

Control relays should not be operated above rated temperature because of resulting increased degradation and fatigue. Common practice is to derate 20 degrees Celsius from the maximum rated temperature limit. Relays operating at rated load are also affected by their environment. Oil vapors may greatly decrease the contact tip life, and dust or dirt may cause the tips to burn before their normal life expectancy. Control relay life cycle varies from 50,000 to over one million cycles depending on the electrical loads of the contacts, duty cycle, application, and the extent to which the relay is derated. When a control relay is operating at its derated value, it is controlling a lower value of current than its maximum make and break ratings. This is often done to extend the operating life of the control relay. The table lists the relay derating factors for typical industrial control applications.

Undesired arcing

Switching while "wet" (under load) causes undesired arcing between the contacts, eventually leading to contacts that weld shut or contacts that fail due to a build up of contact surface damage caused by the destructive arc energy.

Inside the 1ESS switch matrix switch and certain other high-reliability designs, the reed switches are always switched "dry" to avoid that problem, leading to much longer contact life.

Without adequate contact protection, the occurrence of electric current arcing causes significant degradation of the contacts in relays, which suffer significant and visible damage. Every time a relay transitions either from a closed to an open state (break arc) or from an open to a closed state (make arc & bounce arc), under load, an electrical arc can occur between the two contact points (electrodes) of the relay. The break arc is typically more energetic and thus more destructive.

The heat energy contained in the resulting electrical arc is very high (tens of thousands of degrees Fahrenheit), causing the metal on the contact surfaces to melt, pool and migrate with the current. The extremely high temperature of the arc cracks the surrounding gas molecules creating ozone, carbon monoxide, and other compounds. The arc energy slowly destroys the contact metal, causing some material to escape into the air as fine particulate matter. This very activity causes the material in the contacts to degrade quickly, resulting in device failure. This contact degradation drastically limits the overall life of a relay to a range of about 10,000 to 100,000 operations, a level far below the mechanical life of the same device, which can be in excess of 20 million operations.

SOME USEFUL TIPS TO GOOD SOLDERING

2014-05-25T15:51:00.002+05:30

SOME USEFUL TIPS TO GOOD SOLDERING

1. The two surfaces to be soldered should be thoroughly cleaned and made free from any dust, grease or oil. Infact, thorough cleaning of the PCB before beginning the soldering operation and proper tinning of the component leads at the time of soldering that Component achieves good results.

2. A small quantity of flux may be applied on the surfaces to be soldered. It is the function of the soldering ﬂux to keep away any oxide ﬁlm during soldering operation and allow the two surfaces to make a metallic contact and alloy with each other. The flux residue should be removed after the soldering is done.

3. One of the most common problems in soldering is the application of insufficient heat. The alloying action in soldering cannot be achieved without a uniform distribution of heat between the solder and the metal being soldered. If hot solder is applied to a cold metal or a cold solder is applied to a hot metal, there can never be a proper soldering action. Soldering will be proper only when the solder alloy is hot enough to remain in a liquid state as soldering is being done. To achieve a proper wetted soldered joint, heat up the component terminal end slightly (Remember not to exceed the component lead temperature beyond the safe recommended temperature. Excessive temperature can often damage sensitive semiconductor devices) and apply solder alloy right onto the component lead end instead of applying it on the soldering iron tip. Now with the soldering iron tip, melt the solder so that it ﬂows over the joint. Avoid putting excessive solder metal and ensure that it is in the liquid state till it has completely ﬂowed over the joint. A perfect soldered joint would give a shiny bead like appearance.

SOLDERING TEMPERATURES FOR DIFFERENT COMPONENTS

Table lists the typical values of recommended soldering temperatures for different electronic components and devices.

Sl no	Type of Electronic component	Soldering Temperature	Soldering Time
1	General Purpose fixed and variable Resistor	350⁰C	5 seconds
2	Light Dependent Resistors, Varistors, thermistors	250⁰C	-
3	Electrolytic Capacitor	225⁰C	5 seconds
4	Other Capacitor types	200⁰C	Less than 5 seconds
5	Silicone Diodes	250⁰C	5 seconds
6	Germanium Diodes	200⁰C	5 seconds
7	Low Wattage Zener Diodes	200⁰C	10 seconds
8	Light Emitting Diode	150⁰C	10 seconds
9	Power Transistors (in TO-3 and TO-66 package)	275⁰C to 300⁰C	5 seconds
10	Transistors(TO-39, TO-5 package)	225⁰C	5 seconds
11	Transistor(TO-220AB package)	250⁰C	5 seconds
12	Small signal transistors (in TO-92 plastic, TO-72, TO-18, SOT-25 package), FETs, MOSFETs	150⁰C to 200⁰C	-
13	General purpose linear ICs like Opamps, Timers, IC Voltage Regulators, PLLs etc.	250⁰C	5 seconds
14	TTL ICs	175⁰C	10 seconds
15	CMOS ICs	200⁰C to 240⁰C	5 seconds

Fuse (electrical)

2014-04-08T15:28:00.001+05:30

Fuse (electrical)

In electronics and electrical engineering, a fuse (from the French fuser, Italian fuso, "spindle") is a type of low resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source circuit. Its essential component is a metal wire or strip that melts when too much current flows across it, interrupting the circuit that it connects. Short circuits, overloading, mismatched loads or device failure are the prime reasons for excessive current. Fuses are a simple, economical, and low-maintenance alternative to circuit breakers.

A fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented. Wiring regulations often define a maximum fuse current rating for particular circuits. Over current protection devices are essential in electrical systems to limit threats to human life and property damage, including any electrical devices on that circuit. The time and current operating characteristics of fuses are used to provide adequate protection without needless interruption. Slow blow fuses are designed to allow harmless short term currents over their rating while still interrupting a sustained overload. Fuses are manufactured in a wide range of current and voltage ratings to protect wiring systems and electrical equipment. Self-resetting fuses automatically restore the circuit after the overload has cleared, and are useful in environments where a human replacing a blown fuse would be difficult or impossible, for example in aerospace or nuclear applications.

History

In 1847, Breguet recommended use of reduced-section conductors to protect telegraph stations from lightning strikes; by melting, the smaller wires would protect apparatus and wiring inside the building. A variety of wire or foil fusible elements were in use to protect telegraph cables and lighting installations as early as 1864.

A fuse was patented by Thomas Edison in 1890 as part of his successful electric distribution system.

Construction

A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing. The fuse is arranged in series to carry all the current passing through the protected circuit. The resistance of the element generates heat due to the current flow. The size and construction of the element is (empirically) determined so that the heat produced for a normal current does not cause the element to attain a high temperature. If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit.

The fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics. The fuse ideally would carry its rated current indefinitely, and melt quickly on a small excess. The element must not be damaged by minor harmless surges of current, and must not oxidize or change its behavior after possibly years of service.

The fuse elements may be shaped to increase heating effect. In large fuses, current may be divided between multiple strips of metal. A dual-element fuse may contain a metal strip that melts instantly on a short-circuit, and also contain a low-melting solder joint that responds to long-term overload of low values compared to a short-circuit. Fuse elements may be supported by steel or nichrome wires, so that no strain is placed on the element, but a spring may be included to increase the speed of parting of the element fragments.

The fuse element may be surrounded by air, or by materials intended to speed the quenching of the arc. Silica sand or non-conducting liquids may be used.

Characteristic parameters

Rated current I_N

A maximum current that the fuse can continuously conduct without interrupting the circuit.

Speed

The speed at which a fuse blows depends on how much current flows through it and the material of which the fuse is made. The operating time is not a fixed interval, but decreases as the current increases. Fuses have different characteristics of operating time compared to current, characterized as fast-blow, slow-blow, or time-delay, according to time required to respond to an overcurrent condition. A standard fuse may require twice its rated current to open in one second, a fast-blow fuse may require twice its rated current to blow in 0.1 seconds, and a slow-blow fuse may require twice its rated current for tens of seconds to blow.

Fuse selection depends on the load's characteristics. Semiconductor devices may use a fast or ultrafast fuse as semiconductor devices heat rapidly when excess current flows. The fastest blowing fuses are designed for the most sensitive electrical equipment, where even a short exposure to an overload current could be very damaging. Normal fast-blow fuses are the most general purpose fuses. The time delay fuse (also known as anti-surge, or slow-blow) are designed to allow a current which is above the rated value of the fuse to flow for a short period of time without the fuse blowing. These types of fuse are used on equipment such as motors, which can draw larger than normal currents for up to several seconds while coming up to speed.

The I²t value

The amount of energy spent by the fuse element to clear the electrical fault. This term is normally used in short circuit conditions and the values are used to perform co-ordination studies in electrical networks. I²t parameters are provided by charts in manufacturer data sheets for each fuse family. For coordination of fuse operation with upstream or downstream devices, both melting I²t and clearing I²t are specified. The melting I²t, is proportional to the amount of energy required to begin melting the fuse element. The clearing I²t is proportional to the total energy let through by the fuse when clearing a fault. The energy is mainly dependent on current and time for fuses as well as the available fault level and system voltage. Since the I²t rating of the fuse is proportional to the energy it lets through, it is a measure of the thermal damage and magnetic forces that will be produced by a fault.

Breaking capacity

The breaking capacity is the maximum current that can safely be interrupted by the fuse. Generally, this should be higher than the prospective short circuit current. Miniature fuses may have an interrupting rating only 10 times their rated current. Some fuses are designated High Rupture Capacity (HRC) and are usually filled with sand or a similar material. Fuses for small, low-voltage, usually residential, wiring systems are commonly rated, in North American practice, to interrupt 10,000 amperes. Fuses for larger power systems must have higher interrupting ratings, with some low-voltage current-limiting high interrupting fuses rated for 300,000 amperes. Fuses for high-voltage equipment, up to 115,000 volts, are rated by the total apparent power (megavolt-amperes, MVA) of the fault level on the circuit.

Rated voltage

Voltage rating of the fuse must be greater than or equal to what would become the open circuit voltage. For example, a glass tube fuse rated at 32 volts would not reliably interrupt current from a voltage source of 120 or 230 V. If a 32 V fuse attempts to interrupt the 120 or 230 V source, an arc may result. Plasma inside that glass tube fuse may continue to conduct current until current eventually so diminishes that plasma reverts to an insulating gas. Rated voltage should be larger than the maximum voltage source it would have to disconnect. Rated voltage remains same for any one fuse, even when similar fuses are connected in series. Connecting fuses in series does not increase the rated voltage of the combination (nor of any one fuse).

Medium-voltage fuses rated for a few thousand volts are never used on low voltage circuits, because of their cost and because they cannot properly clear the circuit when operating at very low voltages.

Voltage drop

A voltage drop across the fuse is usually provided by its manufacturer. There is a direct relationship between a fuse's cold resistance and its voltage drop value. Once current is applied, resistance and voltage drop of a fuse will constantly grow with the rise of its operating temperature until the fuse finally reaches thermal equilibrium or alternatively melts when higher currents than its rated current are administered over sufficiently long periods of time. This resulting voltage drop should be taken into account, particularly when using a fuse in low-voltage applications. Voltage drop often is not significant in more traditional wire type fuses, but can be significant in other technologies such as resettable fuse (PPTC) type fuses.

Temperature derating

Ambient temperature will change a fuse's operational parameters. A fuse rated for 1 A at 25 °C may conduct up to 10% or 20% more current at −40 °C and may open at 80% of its rated value at 100 °C. Operating values will vary with each fuse family and are provided in manufacturer data sheets.

These are still used in consumer units in some parts of the world, but are becoming less common. While glass fuses have the advantage of a fuse element visible for inspection purposes, they have a low breaking capacity which generally restricts them to applications of 15 A or less at 250 V_AC. Ceramic fuses have the advantage of a higher breaking capacity, facilitating their use in circuits with higher current and voltage. Filling a fuse body with sand provides additional cooling of the arc and increases the breaking capacity of the fuse. Medium-voltage fuses may have liquid-filled envelopes to assist in the extinguishing of the arc. Some types of distribution switchgear use fuse links immersed in the oil that fills the equipment.

Fuse packages may include a rejection feature such as a pin, slot, or tab, which prevents interchange of otherwise similar appearing fuses. For example, fuse holders for North American class RK fuses have a pin that prevents installation of similar-appearing class H fuses, which have a much lower breaking capacity and a solid blade terminal that lacks the slot of the RK type.

Dimensions

Fuses can be built with different sized enclosures to prevent interchange of types of fuse. For example, bottle style fuses distinguish between ratings with different cap diameters. Automotive glass fuses were made in different lengths, to prevent high-rated fuses being installed in a circuit intended for a lower rating.

Special features

Glass cartridge and plug fuses allow direct inspection of the fusible element. Other fuses have other indication methods including:

Indicating pin or striker pin — extends out of the fuse cap when the element is blown.

Indicating disc — a coloured disc (flush mounted in the end cap of the fuse) falls out when the element is blown.

Element window — a small window built into the fuse body to provide visual indication of a blown element.

External trip indicator — similar function to striker pin, but can be externally attached (using clips) to a compatible fuse.

Some fuses allow a special purpose micro switch or relay unit to be fixed to the fuse body. When the fuse element blows, the indicating pin extends to activate the micro switch or relay, which, in turn, triggers an event.

Some fuses for medium-voltage applications use two separate barrels and two fuse elements in parallel.

Markings

Most fuses are marked on the body or end caps with markings that indicate their ratings. Surface-mount technology "chip type" fuses feature few or no markings, making identification very difficult.

Similar appearing fuses may have significantly different properties, identified by their markings. Fuse markings will generally convey the following information, either explicitly as text, or else implicit with the approval agency marking for a particular type:

Ampere rating of the fuse.
Voltage rating of the fuse.
Time-current characteristic; i.e. fuse speed.
Approvals by national and international standards agencies.
Manufacturer/part number/series.
Breaking capacity

Automotive fuses

Automotive fuses are used to protect the wiring and electrical equipment for vehicles. There are several different types of automotive fuses and their usage is dependent upon the specific application, voltage, and current demands of the electrical circuit. Automotive fuses can be mounted in fuse blocks, inline fuse holders, or fuse clips. Some automotive fuses are occasionally used in non-automotive electrical applications. Standards for automotive fuses are published by SAE International (formerly known as the Society of Automotive Engineers).

Automotive fuses can be classified into four distinct categories:

Blade fuses
Glass tube or Bosch type
Fusible links
Fuse limiters

Most automotive fuses rated at 32 volts are used on circuits rated 24 volts DC and below. Some vehicles use a dual 12/42 V DC electrical system that will require a fuse rated at 58 V DC.

High voltage fuses

Fuses are used on power systems up to 115,000 volts AC. High-voltage fuses are used to protect instrument transformers used for electricity metering, or for small powertransformers where the expense of a circuit breaker is not warranted. For example, in distribution systems, a power fuse may be used to protect a transformer serving 1–3 houses. A circuit breaker at 115 kV may cost up to five times as much as a set of power fuses, so the resulting saving can be tens of thousands of dollars. Pole-mounted distribution transformers are nearly always protected by a fusible cutout, which can have the fuse element replaced using live-line maintenance tools.

Large power fuses use fusible elements made of silver, copper or tin to provide stable and predictable performance. High voltage expulsion fuses surround the fusible link with gas-evolving substances, such as boric acid. When the fuse blows, heat from the arc causes the boric acid to evolve large volumes of gases. The associated high pressure (often greater than 100 atmospheres) and cooling gases rapidly quench the resulting arc. The hot gases are then explosively expelled out of the end(s) of the fuse. Such fuses can only be used outdoors.

High voltage high power fuses are standalone protective switching devices used to 115 kV. They are used in power supply networks and for distribution uses. The most frequent application is in transformer circuits, with further uses in motor circuits and capacitor banks. These type of fuses may have an impact pin to operate a switch mechanism, so that all three phases are interrupted if any one fuse blows.

High-power fuse means that these fuses can interrupt several kiloamperes. Some manufacturers have tested their fuses for up to 63 kA cut-off current.

Fuses compared with circuit breakers

Fuses have the advantages of often being less costly and simpler than a circuit breaker for similar ratings. The blown fuse must be replaced with a new device which is less convenient than simply resetting a breaker and therefore likely to discourage people from ignoring faults. On the other hand, replacing a fuse without isolating the circuit first (most building wiring designs do not provide individual isolation switches for each fuse) can be dangerous in itself, particularly if the fault is a short circuit.

High rupturing capacity fuses can be rated to safely interrupt up to 300,000 amperes at 600 V AC. Special current-limiting fuses are applied ahead of some molded-case breakers to protect the breakers in low-voltage power circuits with high short-circuit levels.

Current-limiting fuses operate so quickly that they limit the total "let-through" energy that passes into the circuit, helping to protect downstream equipment from damage. These fuses open in less than one cycle of the AC power frequency; circuit breakers cannot match this speed.

Some types of circuit breakers must be maintained on a regular basis to ensure their mechanical operation during an interruption. This is not the case with fuses, which rely on melting processes where no mechanical operation is required for the fuse to operate under fault conditions.

In a multi-phase power circuit, if only one fuse opens, the remaining phases will have higher than normal currents, and unbalanced voltages, with possible damage to motors. Fuses only sense overcurrent, or to a degree, over-temperature, and cannot usually be used independently with protective relaying to provide more advanced protective functions, for example, ground fault detection.

Some manufacturers of medium-voltage distribution fuses combine the overcurrent protection characteristics of the fusible element with the flexibility of relay protection by adding a pyrotechnic device to the fuse operated by external protective relays.

Fuse boxes

In the UK, older electrical consumer units (also called fuse boxes) are fitted either with semi-enclosed (rewirable) fuses (BS 3036) or cartridge fuses (BS 1361). (Fuse wire is commonly supplied to consumers as short lengths of 5 A-, 15 A- and 30 A-rated wire wound on a piece of cardboard.) Modern consumer units usually contain miniature circuit breakers (MCBs) instead of fuses, though cartridge fuses are sometimes still used, as MCBs are prone to nuisance tripping.

Renewable fuses (rewirable or cartridge) allow user replacement, but this can be hazardous as it is easy to put a higher-rated or double fuse element (link or wire) into the holder (overfusing), or simply fitting it with copper wire or even a totally different type of conducting object (coins, hairpins, paper clips, nails, etc.) to the existing carrier. One form of fuse box abuse was to put a penny in the socket, which defeated overcurrent protection and resulted in a dangerous condition. Such tampering will not be visible without full inspection of the fuse. Fuse wire was never used in North America for this reason, although renewable fuses continue to be made for distribution boards.

Other fuse types

Resettable fuses

So-called self-resetting fuses use a thermoplastic conductive element known as a Polymeric Positive Temperature Coefficient (or PPTC) thermistor that impedes the circuit during an overcurrent condition (by increasing device resistance). The PPTC thermistor is self-resetting in that when current is removed, the device will cool and revert to low resistance. These devices are often used in aerospace/nuclear applications where replacement is difficult, or on a computer motherboard so that a shorted mouse or keyboard does not cause motherboard damage.

Thermal fuses

A thermal fuse is often found in consumer equipment such as coffee makers, hair dryers or transformerspowering small consumer electronics devices. They contain a fusible, temperature-sensitive alloy which holds a spring contact mechanism normally closed. When the surrounding temperature gets too high, the alloy melts and allows the spring contact mechanism to break the circuit. The device can be used to prevent a fire in a hair dryer for example, by cutting off the power supply to the heater elements when the air flow is interrupted (e.g., the blower motor stops or the air intake becomes accidentally blocked). Thermal fuses are a 'one shot', non-resettable device which must be replaced once they have been activated (blown).

Create your own ANDROID apps

2014-03-02T18:42:00.000+05:30

Create your own ANDROID apps

Get the Android SDK

The Android SDK provides you the API libraries and developer tools necessary to build, test, and debug apps for Android.
If you're a new Android developer, we recommend you download the ADT Bundle to quickly start developing apps. It includes the essential Android SDK components and a version of the Eclipse IDE with built-in ADT (Android Developer Tools) to streamline your Android app development.
With a single download, the ADT Bundle includes everything you need to begin developing apps:

Eclipse + ADT plugin
Android SDK Tools
Android Platform-tools
The latest Android platform
The latest Android system image for the emulator

I have read and agree with the Terms and Conditions

32-bit 64-bit

Download the SDK ADT Bundle for Windows

Android Studio Early Access Preview

A new Android development environment called Android Studio, based on IntelliJ IDEA, is now available as an early access preview. For more information, see Getting Started with Android Studio.

Portions of this page are reproduced from work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

Blu-ray Disc

2014-02-19T14:44:00.000+05:30

Blu-ray Disc

Blu-ray Disc (BD) is a digital optical disc data storage format designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Conventional (pre-BD-XL) Blu-ray Discs contain 25 GB per layer, with dual layer discs (50 GB) being the industry standard for feature-length video discs. Triple layer discs (100 GB) and quadruple layers (128 GB) are available for BD-XL re-writer drives. The name Blu-ray Disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs.

The major application of Blu-ray Discs is as a medium for video material such as feature films. Besides the hardware specifications, Blu-ray Disc is associated with a set of multimedia formats. Generally, these formats allow for the video and audio to be stored with greater definition than on DVD.

The format was developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. Sony unveiled the first Blu-ray Disc prototypes in October 2000, and the first prototype player was released in April 2003 in Japan. Afterwards, it continued to be developed until its official release in June 2006. As of June 2008, more than 2,500 Blu-ray Disc titles were available in Australia and the United Kingdom, with 3,500 in the United States and Canada. In Japan, as of July 2010, more than 3,300 titles have been released.

During the high definition optical disc format war, Blu-ray Disc competed with the HD DVD format. Toshiba, the main company that supported HD DVD, conceded in February 2008, releasing its own Blu-ray Disc player in late 2009.

Media type	High-density optical disc
Encoding	H.262/MPEG-2 Part 2 H.264/MPEG-4 AVC VC-1
Capacity	25 GB (single-layer) 50 GB (dual-layer) 100/128 GB (BDXL)
Block size	64 KB ECC
Read mechanism	405 nm diode laser
Developed by	Blu-ray Disc Association
Dimensions	120 mm (4.7 in) diameter 1.2 mm thickness
Usage	Data storage High-definition video (1080p) High-definition audio Stereoscopic 3D PlayStation 3 games PlayStation 4 games Xbox One games

History

The information density of the DVD format was limited by the wavelength of the laser diodes used. Following protracted development, blue laser diodes operating at 405 nanometers became available on a production basis. Sony started two projects in collaboration with Philips applying the new diodes: UDO (Ultra Density Optical), and DVR Blue (together with Pioneer), a format of rewritable discs that would eventually become Blu-ray Disc (more specifically, BD-RE). The core technologies of the formats are similar.

The first DVR Blue prototypes were unveiled at the CEATEC exhibition in October 2000 by Sony. A trademark for the "Blue Disc" logo was filed February 9, 2001. On February 19, 2002, the project was officially announced as Blu-ray Disc, and Blu-ray Disc Founders was founded by the nine initial members.
The first consumer device arrived in stores on April 10, 2003: the Sony BDZ-S77, a $3,800 (US) BD-RE recorder that was made available only in Japan. But there was no standard for prerecorded video, and no movies were released for this player.

Hollywood studios insisted that players be equipped with digital rights management before they would release movies for the new format, and they wanted a new DRM system that would be more secure than the failed Content Scramble System (CSS) used on DVDs.

On October 4, 2004, the name "Blu-ray Disc Founders" was officially changed to the Blu-ray Disc Association (BDA), and 20th Century Fox joined the BDA's Board of Directors.
The Blu-ray Disc physical specifications were completed in 2004.

AACS LA, a consortium founded in 2004, had been developing the DRM platform that could be used to securely distribute movies to consumers. However, the final AACS standard was delayed,^[23] and then delayed again when an important member of the Blu-ray Disc group voiced concerns. At the request of the initial hardware manufacturers, including Toshiba, Pioneer, and Samsung, an interim standard was published that did not include some features, such as managed copy.

Competition from HD DVD

The DVD Forum, chaired by Toshiba, was split over whether to develop the more expensive blue laser technology. In March 2002, the forum approved a proposal endorsed by Warner Bros. and other motion picture studios that involved compressing HD content onto dual-layer standard DVD-9 discs. In spite of this decision, however, the DVD Forum's Steering Committee announced in April that it was pursuing its own blue-laser high-definition video solution. In August, Toshiba and NEC announced their competing standard, Advanced Optical Disc. It was finally adopted by the DVD Forum and renamed HD DVD the next year,after being voted down twice by DVD Forum members who were also Blu-ray Disc Association members—a situation that drew preliminary investigations by the U.S. Department of Justice.

HD DVD had a head start in the high-definition video market, as Blu-ray Disc sales were slow to gain market share. The first Blu-ray Disc player was perceived as expensive and buggy, and there were few titles available.
The appearance of the Sony PlayStation 3, which contained a Blu-ray Disc player for primary storage, helped support Blu-ray. Sony also ran a more thorough and influential marketing campaign for the format. 2006 also saw the launch of AVCHD camcorders, whose recordings can be played back on many Blu-ray Disc players without re-encoding, but not on HD DVD players.

By January 2007, Blu-ray Discs had outsold HD DVDs, and during the first three-quarters of 2007, BD outsold HD DVD by about two to one. At CES 2007, Warner proposed Total Hi Def—a hybrid disc containing Blu-ray on one side and HD DVD on the other, but it was never released.

Physical media

Laser and optics

While a DVD uses a 650 nm red laser, Blu-ray Disc uses a 405 nm "blue" laser diode. Note that even though the laser is called "blue", its color is actually in the violet range. The shorter wavelength can be focused to a smaller area, thus enabling it to read information recorded in pits that are less than half the size of those on a DVD, and can consequently be spaced more closely, resulting in a shorter track pitch, enabling a Blu-ray Disc to hold about five times the amount of information that can be stored on a DVD.
The lasers are GaN (gallium nitride) laser diodes that produce 405 nm light directly, that is, without frequency doubling or other nonlinear optical mechanisms. Conventional DVDs use 650 nm red lasers, and CDs use 780 nm near-infrared lasers.

The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85, and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot, which effectively allows more information to be stored in the same area. For Blu-ray Disc, the spot size is 580 nm. This allows a reduction of the pit size from 400 nm for DVD to 150 nm for Blu-ray Disc, and of the track pitch from 740 nm to 320 nm. See Compact Disc for information on optical discs' physical structure.

In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding that further increase the amount of content that can be stored.

Hard-coating technology

Since the Blu-ray Disc data layer is closer to the surface of the disc compared to the DVD standard, it was at first more vulnerable to scratches. The first discs were housed in cartridges for protection, resembling Professional Discs introduced by Sony in 2003.

Using a cartridge would increase the price of an already expensive medium, so hard-coating of the pickup surface was chosen instead. TDK was the first company to develop a working scratch-protection coating for Blu-ray Discs. It was named Durabis. In addition, both Sony and Panasonic's replication methods include proprietary hard-coat technologies. Sony's rewritable media are spin-coated, using a scratch-resistant and antistatic coating. Verbatim's recordable and rewritable Blu-ray Discs use their own proprietary technology, called Hard Coat.
The Blu-ray Disc specification requires the testing of resistance to scratches by mechanical abrasion. In contrast, DVD media are not required to be scratch-resistant, but since development of the technology, some companies, such as Verbatim, implemented hard-coating for more expensive lineups of recordable DVDs.

Recording speed

If a USB 2.0 interface is used, the maximum drive speed is 8× (288 Mbit/s or 36 MB/s). A USB 3.0 interface (with proper cabling) does not have this limitation, and is capable of handling Blu-ray drive speeds far in excess of what is currently possible. The 5.25-inch (13.3 cm) width Blu-ray drives for desktop computer drive bays have a Serial ATA (SATA) interface. Even the oldest version of SATA has a transfer rate of 1.2 Gbit/s (150 MB/s), which is more than twice the demand of the 16× speed.
Note that interface speeds commonly advertise total throughput (for example, USB 2.0's 480 Mbit/s) that includes overhead such as the encoding scheme or error correction. Only the actual transfer speeds should be used to compare the interface with the drive speed.

Packaging

Prerecorded Blu-ray Disc titles usually ship in packages similar but slightly smaller (18.5 mm shorter and 1 mm thinner: 135 mm x 171.5 mm x 13 mm.) than a standard DVD keep case, generally with the format prominently displayed in a horizontal stripe across the top of the case (blue for Blu-ray, red for PlayStation 3 Greatest Hits Games, and clear for PlayStation 3 regular games). PlayStation 4 and Xbox One introduced new packaging for their games; unlike the PlayStation 3, PlayStation 4 now has blue cases much like the regular Blu-ray Disc cases, while Xbox One introduced a green case for their games.

Variants

Mini Blu-ray Disc

The "Mini Blu-ray Disc" (also, "Mini-BD" and "Mini Blu-ray") is a compact 8 cm (~3 in)-diameter variant of the Blu-ray Disc that can store approximately 7.8 GB of data. It is similar in concept to the MiniDVD and MiniCD. Recordable (BD-R) and rewritable (BD-RE) versions of Mini Blu-ray Disc have been developed specifically for compact camcorders and other compact recording devices.

Blu-ray Disc recordable

"Blu-ray Disc recordable" refers to two optical disc formats that can be recorded with an optical disc recorder. BD-Rs can be written to once, whereas BD-REs can be erased and re-recorded multiple times. The current practical maximum speed for Blu-ray Discs is about 12×. Higher speeds of rotation (10,000+ rpm) cause too much wobble for the discs to be written properly, as with the 20× and 52× maximum speeds, respectively, of standard DVDs and Cs.

Since September 2007, BD-RE is also available in the smaller 8 cm Mini Blu-ray Disc size.
On September 18, 2007, Pioneer and Mitsubishi codeveloped BD-R LTH ("Low to High" in groove recording), which features an organic dye recording layer that can be manufactured by modifying existing CD-R and DVD-R production equipment, significantly reducing manufacturing costs. In February 2008, Taiyo Yuden, Mitsubishi, and Maxell released the first BD-R LTH Discs, and in March 2008, Sony's PlayStation 3 gained official support for BD-R LTH Discs with the 2.20 firmware update. In May 2009 Verbatim/Mitsubishi announced the industry's first 6X BD-R LTH media, which allows recording a 25 GB disc in about 16 minutes.
Unlike the previous releases of 120 mm optical discs (i.e., CDs and standard DVDs), Blu-ray recorders hit the market almost simultaneously with Blu-ray's debut.

BD9 and BD5

The BD9 format was proposed to the Blu-ray Disc Association by Warner Home Video as a cost-effective alternative to the 25/50 GB BD-ROM discs. The format was supposed to use the same codecs and program structure as Blu-ray Disc video, but recorded onto less expensive 8.5 GB dual-layer DVD. This red-laser media could be manufactured on existing DVD production lines with lower costs of production than the 25/50 GB Blu-ray media.

Usage of BD9 for releasing content on "pressed" discs has never caught on. After the end of the format war, major producers ramped up the production of Blu-ray Discs and lowered their prices to the level of DVDs. On the other hand, the idea of using inexpensive DVD media became popular among individual users. A lower-capacity version of this format that uses single-layer 4.7 GB DVDs has been unofficially called BD5. Both formats are being used by individuals for recording high definition content in Blu-ray format onto recordable DVD media.

Despite the fact that the BD9 format has been adopted as part of the BD-ROM basic format, none of the existing Blu-ray player models support it explicitly. As such, the discs recorded in BD9 and BD5 formats are not guaranteed to play on standard Blu-ray Disc players.
AVCHD and AVCREC also use inexpensive media like DVDs, but unlike BD9 and BD5 these formats have limited interactivity, codec types, and data rates.
As of March 2011, BD9 was removed as an official BD-ROM disc.

BDXL

The BDXL format supports 100 GB and 128 GB write-once discs and 100 GB rewritable discs for commercial applications. It was defined in June 2010.

BD-R 3.0 Format Specification (BDXL) defined a multi-layered disc recordable in BDAV format with the speed of 2× and 4×, capable of 100/128 GB and usage of UDF2.5/2.6.

BD-RE 4.0 Format Specification (BDXL) defined a multi-layered disc rewritable in BDAV with the speed of 2× and 4×, capable of 100 GB and usage of UDF2.5 as file system.

IH-BD

The IH-BD (Intra-Hybrid Blu-ray) format includes a 25 GB re-writable layer (BD-RE) and a 25 GB write once layer (BD-ROM), designed to work with existing Blu-ray Discs.

Software standards

Filesystem

Blu-ray Disc specifies the use of Universal Disk Format (UDF) 2.50 as a convergent friendly format for both PC and consumer electronics environments. It is used in the latest specifications of BD-ROM, BD-RE and BD-R.
In the first BD-RE specification (defined in 2002), the BDFS (Blu-ray Disc File System) was used. The BD-RE 1.0 specification was defined mainly for the digital recording of High-definition television (HDTV) broadcast television. The BDFS was replaced by UDF 2.50 in the second BD-RE specification in 2005, in order to enable interoperability among consumer electronics Blu-ray recorders and personal computer systems. These optical disc recording technologies enabled PC recording and playback of BD-RE. BD-R can use UDF 2.50/2.60.
The Blu-ray Disc application (BDAV application) for recording of digital broadcasting has been developed as System Description Blu-ray Rewritable Disc Format part 3 Audio Visual Basic Specifications. The requirements related with computer file system have been specified in System Description Blu-ray Rewritable Disc Format part 2 File System Specifications version 1.0 (BDFS).

Initially, the BD-RE version 1.0 (BDFS) was specifically developed for recording of digital broadcasting using the Blu-ray Disc application (BDAV application). To support UDF, these requirements are superseded by the Blu-ray Rewritable Disc File System Specifications version 2.0 (UDF) (a.k.a. RE 2.0) and Blu-ray Recordable Disc File System Specifications version 1.0 (UDF) (a.k.a. R 1.0). Additionally, a new application format, BDMV (System Description Blu-ray Disc Prerecorded Format part 3 Audio Visual Basic Specifications) for High Definition Content Distribution was developed for BD-ROM. The only file system developed for BDMV is the System Description Blu-ray Read-Only Disc Format part 2 File System Specifications version 1.0 (UDF) which defines the requirements for UDF 2.50.

Media format

Container format

Audio, video and other streams are multiplexed and stored on Blu-ray Discs in a container format based on the MPEG transport stream. It is also known as BDAV MPEG-2 transport stream and can use filename extension .m2ts. Blu-ray Disc titles authored with menu support are in the BDMV (Blu-ray Disc Movie) format and contain audio, video, and other streams in BDAV container. There is also the BDAV (Blu-ray Disc Audio/Visual) format, the consumer oriented alternative to the BDMV format used for movie releases. The BDAV format is used on BD-REs and BD-Rs for audio/video recording. BDMV format was later defined also for BD-RE and BD-R (in September 2006, in the third revision of BD-RE specification and second revision of BD-R specification).

Blu-ray Disc employs the MPEG transport stream recording method. That enables transport streams of digital broadcasts to be recorded as they are broadcast, without altering the format. It also enables flexible editing of a digital broadcast that is recorded as is and where the data can be edited just by rewriting the playback stream. Although it is quite natural, a function for high-speed and easy-to use retrieval is built in. Blu-ray Disc Video use MPEG transport streams, compared to DVD's MPEG program streams. This allows multiple video programs to be stored in the same file so they can be played back simultaneously (e.g., with "picture-in-picture" effect).

Codecs

The BD-ROM specification mandates certain codec compatibilities for both hardware decoders (players) and movie software (content). Windows Media Player does not come with the codecs required to play Blu-ray discs.

Video

High-definition video may be stored on BD-ROMs with up to 1920×1080 pixel resolution at up to 60 (59.94) fields per second. Officially, progressive scan video can go up to 1920×1080 pixel resolution at 24 frames per second, or up to 59.94 frames per second at a resolution of 1280×720 pixels. Many current Blu-ray players and recorders now support 1920×1080 video at the full 60p and 50p progressive format.

For video, all players are required to support H.262/MPEG-2 Part 2, H.264/MPEG-4 Part 10: AVC, and SMPTE VC-1. BD-ROM titles with video must store video using one of the three mandatory formats; multiple formats on a single title are allowed. Blu-ray Disc supports video with a bit depth of 8-bits per color YCbCr with 4:2:0 chroma subsampling.

The choice of formats affects the producer's licensing/royalty costs as well as the title's maximum run time, due to differences in compression efficiency. Discs encoded in MPEG-2 video typically limit content producers to around two hours of high-definition content on a single-layer (25 GB) BD-ROM. The more-advanced video formats (VC-1 and MPEG-4 AVC) typically achieve a video run time twice that of MPEG-2, with comparable quality.

MPEG-2 was used by many studios (including Paramount Pictures, which initially used the VC-1 format for HD DVD releases) for the first series of Blu-ray Discs, which were launched throughout 2006. Modern releases are now often encoded in either MPEG-4 AVC or VC-1, allowing film studios to place all content on one disc, reducing costs and improving ease of use. Using these formats also frees a lot of space for storage of bonus content in HD (1080i/p), as opposed to the SD (480i/p) typically used for most titles. Some studios, such as Warner Bros., have released bonus content on discs encoded in a different format than the main feature title. For example, the Blu-ray Disc release of Superman Returns uses VC-1 for the feature film and MPEG-2 for some of its bonus content. Today, Warner and other studios typically provide bonus content in the video format that matches the feature.

Audio

For audio, BD-ROM players are required to support Dolby Digital (AC-3), DTS, and linear PCM. Players may optionally support Dolby Digital Plus and DTS-HD High Resolution Audio
as well as lossless formats Dolby TrueHD and DTS-HD Master Audio. BD-ROM titles must use one of the mandatory schemes for the primary soundtrack. A secondary audiotrack, if present, may use any of the mandatory or optional codecs.

Bit rate

For users recording digital television programming, the recordable Blu-ray Disc standard's initial data rate of 36 Mbit/s is more than adequate to record high-definition broadcasts from any source (IPTV, cable/satellite, or terrestrial). BD Video movies have a maximum data transfer rate of 54 Mbit/s, a maximum AV bitrate of 48 Mbit/s (for both audio and video data), and a maximum video bit rate of 40 Mbit/s. This compares to HD DVD movies, which have a maximum data transfer rate of 36 Mbit/s, a maximum AV bitrate of 30.24 Mbit/s, and a maximum video bitrate of 29.4 Mbit/s.

Application format

BDAV or BD-AV (Blu-ray Disc Audio/Visual): a consumer-oriented Blu-ray video format used for audio/video recording (defined in 2002).
BDMV or BD-MV (Blu-ray Disc Movie): a Blu-ray video format with menu support commonly used for movie releases.
BDMV Recording specification (defined in September 2006 for BD-RE and BD-R).
RREF (Realtime Recording and Editing Format): a subset of BDMV designed for realtime recording and editing applications.
HFPA (High Fidelity Pure Audio): A high definition audio disc using the Blu-ray format

Java software support

Main article: BD-J

At the 2005 JavaOne trade show, it was announced that Sun Microsystems' Java cross-platform software environment would be included in all Blu-ray Disc players as a mandatory part of the standard. Java is used to implement interactive menus on Blu-ray Discs, as opposed to the method used on DVD-video discs. DVDs use pre-rendered MPEG segments and selectable subtitle pictures, which are considerably more primitive and rarely seamless. At the conference, Java creator James Gosling suggested that the inclusion of a Java virtual machine, as well as network connectivity in some BD devices, will allow updates to Blu-ray Discs via the Internet, adding content such as additional subtitle languages and promotional features not included on the disc at pressing time. This Java Version is called BD-J and is built on a profile of the Globally Executable MHP (GEM) standard; GEM is the worldwide version of the Multimedia Home Platform standard.

Player profiles

The BD-ROM specification defines four Blu-ray Disc player profiles, including an audio-only player profile (BD-Audio) that does not require video decoding or BD-J. All of the video-based player profiles (BD-Video) are required to have a full implementation of BD-J, with varying levels of hardware support.

On November 2, 2007, the Grace Period Profile was superseded by Bonus View as the minimum profile for new BD-Video players released to the market. When Blu-ray Disc software not authored with interactive features dependent on Bonus View or BD-Live hardware capabilities is played on Profile 1.0 players, it is able to play the main feature of the disc, but some extra features may not be available or will have limited capability.

BD-Live

The biggest difference between Bonus View and BD-Live is that BD-Live requires the Blu-ray Disc player to have an Internet connection to access Internet-based content. BD-Live features have included Internet chats, scheduled chats with the director, Internet games, downloadable featurettes, downloadable quizzes, and downloadable movie trailers. Note that while some Bonus View players may have an Ethernet port, these are used for firmware updates and are not used for Internet-based content. In addition, Profile 2.0 also requires more local storage in order to handle this content.

With the exception of the latest players and the PlayStation 3, Profile 1.0 players cannot be upgraded to be Bonus View or BD-Live compliant.

Backward compatibility

Though not compulsory, the Blu-ray Disc Association recommends that Blu-ray Disc drives be capable of reading standard DVDs and CDs, for backward compatibility. A few early Blu-ray Disc players released in 2006 could play DVDs but not CDs.

Variations

AVCHD

AVCHD was originally developed as a high definition format for consumer tapeless camcorders. Derived from the Blu-ray Disc specification, AVCHD shares a similar random access directory structure, but is restricted to lower audio and video bitrates, simpler interactivity, and the use of AVC-video and Dolby AC-3 (or linear PCM) audio.

Being primarily an acquisition format, AVCHD playback is not universally supported by all devices that support Blu-ray Disc playback. Nevertheless, many such devices are capable of playing AVCHD recordings from removable media, such as DVDs, SD/SDHC memory cards, "Memory Stick" cards, and hard disk drives.

AVCREC

AVCREC uses a BDAV container to record high definition content on conventional DVDs. Presently AVCREC is tightly integrated with the Japanese ISDB broadcast standard and is not marketed outside of Japan. AVCREC is used primarily in set-top digital video recorders and in this regard is comparable to HD REC.

Blu-ray 3D

The Blu-ray Disc Association (BDA) created a task force made up of executives from the film industry and the consumer electronics and IT sectors to help define standards for putting 3D film and 3D television content on a Blu-ray Disc. On December 17, 2009, the BDA officially announced 3D specs for Blu-ray Disc, allowing backward compatibility with current 2D Blu-ray players. The BDA has said, "The Blu-ray 3D specification calls for encoding 3D video using the "Stereo High" profile defined by Multiview Video Coding (MVC), an extension to the ITU-T H.264 Advanced Video Coding (AVC) codec currently supported by all Blu-ray Disc players. MPEG4-MVC compresses both left and right eye views with a typical 50% overhead compared to equivalent 2D content, and can provide full 1080p resolution backward compatibility with current 2D Blu-ray Disc players." This means the MVC (3D) stream is backward compatible with H.264/AVC (2D) stream, allowing older 2D devices and software to decode stereoscopic video streams, ignoring additional information for the second view.

Sony has released a firmware upgrade for PlayStation 3 consoles that enables 3D Blu-ray Disc playback. It previously released support for 3D gaming on April 21, 2010 (followed by the availability of 3D movies). Since the version 3.70 software update in August 9, 2011, the PlayStation 3 can support DTS-HD Master Audio and DTS-HD High Resolution Audio while playing 3D Blu-ray. Dolby TrueHD is used on a small minority of Blu-ray 3D releases, and bitstreaming is supported by slim PlayStation 3 models only (fat PS3 models decode internally and send audio as LPCM).

Radar

2014-02-06T15:34:00.001+05:30

RADAR

Radar is an object-detection system that uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaves that bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna that is usually located at the same site as the transmitter.

Radar was secretly developed by several nations before and during World War II. The term RADAR itself, not the actual development, was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging. The term radar has since entered English and other languages as the common noun radar, losing all capitalization.

The modern uses of radar are highly diverse, including air traffic control, radar astronomy, air-defense systems, antimissile systems; marine radars to locate landmarks and other ships; aircraft anticollision systems; ocean surveillance systems, outer space surveillance and rendezvous systems; meteorological precipitation monitoring; altimetry and flight control systems; guided missile target locating systems; and ground-penetrating radar for geological observations. High tech radar systems are associated with digital signal processing and are capable of extracting useful information from very high noise levels.

Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar", which uses visible light from lasers rather than radio waves.

History

As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter. In 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation.

The German inventor Christian Hülsmeyer was the first to use radio waves to detect "the presence of distant metallic objects". In 1904 he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter. He obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also got a British patent on September 23, 1904 for a full system, that he called a telemobiloscope.

In April 1940, Popular Science showed an example of a radar unit using the Watson-Watt patent in an article on air defence, but not knowing that the U.S. Army and U.S. Navy were working on radars with the same principle, stated under the illustration, "This is not U.S. Army equipment." Also, in late 1941 Popular Mechanics had an article in which a U.S. scientist speculated about the British early warning system on the English east coast and came close to what it was and how it worked. Alfred Lee Loomis organized the Radiation Laboratory at Cambridge, Massachusetts which developed the technology in the years 1941-45. Later, in 1943, Page greatly improved radar with the monopulse technique that was used for many years in most radar applications.

The war precipitated research to find better resolution, more portability, and more features for radar, including complementary navigation systems like Oboe used by the RAF's Pathfinder.

Applications

The information provided by radar includes the bearing and range (and therefore position) of the object from the radar scanner. It is thus used in many different fields where the need for such positioning is crucial. The first use of radar was for military purposes: to locate air, ground and sea targets. This evolved in the civilian field into applications for aircraft, ships, and roads.

In aviation, aircraft are equipped with radar devices that warn of aircraft or other obstacles in or approaching their path, display weather information, and give accurate altitude readings. The first commercial device fitted to aircraft was a 1938 Bell Lab unit on some United Air Lines aircraft. Such aircraft can land in fog at airports equipped with radar-assisted ground-controlled approach systems in which the plane's flight is observed on radar screens while operators radio landing directions to the pilot.

Marine radars are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate, and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships. In port or in harbour, vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters.

Meteorologists use radar to monitor precipitation and wind. It has become the primary tool for short-term weather forecasting and watching for severe weather such as thunderstorms, tornadoes, winter storms, precipitation types, etc. Geologists use specialised ground-penetrating radars to map the composition of Earth's crust.

Police forces use radar guns to monitor vehicle speeds on the roads.

Principles

A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity—especially by most metals, by seawater and by wet lands. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either toward or away from the transmitter, there is a slight equivalent change in the frequency of the radio waves, caused by the Doppler effect.

Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals.

The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended.

Radar relies on its own transmissions rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, although radio waves are invisible to the human eye or optical cameras.

Reflection

If electromagnetic waves traveling through one material meet another, having a very different dielectric constant or diamagnetic constant from the first, the waves will reflect or scatter from the boundary between the materials. This means that a solid object in air or in a vacuum, or a significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves from its surface. This is particularly true for electrically conductive materials such as metal and carbon fiber, making radar well-suited to the detection of aircraft and ships. Radar absorbing material, containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection. This is the radio equivalent of painting something a dark color so that it cannot be seen by the eye at night.

Radar waves scatter in a variety of ways depending on the size (wavelength) of the radio wave and the shape of the target. If the wavelength is much shorter than the target's size, the wave will bounce off in a way similar to the way light is reflected by a mirror. If the wavelength is much longer than the size of the target, the target may not be visible because of poor reflection. Low-frequency radar technology is dependent on resonances for detection, but not identification, of targets. This is described by Rayleigh scattering, an effect that creates Earth's blue sky and red sunsets. When the two length scales are comparable, there may be resonances. Early radars used very long wavelengths that were larger than the targets and thus received a vague signal, whereas some modern systems use shorter wavelengths (a few centimeters or less) that can image objects as small as a loaf of bread.

Short radio waves reflect from curves and corners in a way similar to glint from a rounded piece of glass. The most reflective targets for short wavelengths have 90° angles between the reflective surfaces. A corner reflector consists of three flat surfaces meeting like the inside corner of a box. The structure will reflect waves entering its opening directly back to the source. They are commonly used as radar reflectors to make otherwise difficult-to-detect objects easier to detect. Corner reflectors on boats, for example, make them more detectable to avoid collision or during a rescue. For similar reasons, objects intended to avoid detection will not have inside corners or surfaces and edges perpendicular to likely detection directions, which leads to "odd" looking stealth aircraft. These precautions do not completely eliminate reflection because of diffraction, especially at longer wavelengths. Half wavelength long wires or strips of conducting material, such as chaff, are very reflective but do not direct the scattered energy back toward the source. The extent to which an object reflects or scatters radio waves is called its radar cross section.

Radar equation

The power P_r returning to the receiving antenna is given by the equation:

where,

P_t = transmitter power
G_t = gain of the transmitting antenna
A_r = effective aperture (area) of the receiving antenna
σ = radar cross section, or scattering coefficient, of the target
F = pattern propagation factor
R_t = distance from the transmitter to the target
R_r = distance from the target to the receiver.

In the common case where the transmitter and the receiver are at the same location, R_t = R_r and the term R_t² R_r² can be replaced by R⁴, where R is the range. This yields:

This shows that the received power declines as the fourth power of the range, which means that the received power from distant targets is relatively very small.

Additional filtering and pulse integration modifies the radar equation slightly for pulse-Doppler radar performance, which can be used to increase detection range and reduce transmit power.

The equation above with F = 1 is a simplification for transmission in a vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment. In a real-world situation, pathloss effects should also be considered.

Doppler effect

Frequency shift is caused by motion that changes the number of wavelengths between the reflector and the radar. That can degrade or enhance radar performance depending upon how that affects the detection process. As an example, Moving Target Indication can interact with Doppler to produce signal cancellation at certain radial velocities, which degrades performance.

Sea-based radar systems, semi-active radar homing, weather radar, military aircraft, and radar astronomy rely on the Doppler effect to enhance performance. This produces information about target velocity during the detection process. This also allows small objects to be detected in an environment containing much larger nearby slow moving objects.

Doppler shift depends upon whether the radar configuration is active or passive. Active radar transmits a signal that is reflected back to the receiver. Passive radar depends upon the object sending a signal to the receiver.

The Doppler frequency shift for active radar is as follows, where is Doppler frequency, is transmit frequency, is radial velocity, and is the speed of light:

Passive radar is applicable to electronic countermeasures and radio astronomy as follows:

Only the radial component of the speed is relevant. When the reflector is moving at right angle to the radar beam, it has no relative velocity. Vehicles and weather moving parallel to the radar beam produce the maximum Doppler frequency shift.

Doppler measurement is reliable only if the sampling rate exceeds the Nyquist frequency for the frequency shift produced by radial motion. As an example, Doppler weather radar with a pulse rate of 2 kHz and transmit frequency of 1 GHz can reliably measure weather up to 150 m/s (330 mile/hour), but cannot reliably determine radial velocity of aircraft moving 1,000 m/s (3,300 mile/hour).

Polarization

In all electromagnetic radiation, the electric field is perpendicular to the direction of propagation, and this direction of the electric field is the polarization of the wave. In the transmitted radar signal the polarization can be controlled for different effects. Radars use horizontal, vertical, linear and circular polarization to detect different types of reflections. For example, circular polarization is used to minimize the interference caused by rain. Linear polarization returns usually indicate metal surfaces. Random polarization returns usually indicate a fractal surface, such as rocks or soil, and are used by navigation radars.

Limiting factors

Beam path and range

The radar beam would follow a linear path in vacuum, but it really follows a somewhat curved path in the atmosphere because of the variation of the refractive index of air, that is called the radar horizon. Even when the beam is emitted parallel to the ground, it will rise above it as the Earth curvature sinks below the horizon. Furthermore, the signal is attenuated by the medium it crosses, and the beam disperses.The maximum range of a conventional radar can be limited by a number of factors:

Line of sight, which depends on height above ground. This means with out a direct line of sight the path of the beam is blocked.

The maximum non-ambiguous range, which is determined by the pulse repetition frequency. The maximum non-ambiguous range is the distance the pulse could travel and return before the next pulse is emitted.

Radar sensitivity and power of the return signal as computed in the radar equation. This includes factors such as environmental conditions and the size (or radar cross section) of the target.

Noise

Signal noise is an internal source of random variations in the signal, which is generated by all electronic components.

Reflected signals decline rapidly as distance increases, so noise introduces a radar range limitation. The noise floor and signal to noise ratio are two different measure of performance that impact range performance. Reflectors that are too far away produce too little signal to exceed the noise floor and cannot be detected. Detection requires a signal that exceeds the noise floor by at least the signal to noise ratio.

Noise typically appears as random variations superimposed on the desired echo signal received in the radar receiver. The lower the power of the desired signal, the more difficult it is to discern it from the noise. Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver, and this needs to be minimized.

Shot noise is produced by electrons in transit across a discontinuity, which occurs in all detectors. Shot noise is the dominant source in most receivers. There will also be flicker noise caused by electron transit through amplification devices, which is reduced using heterodyne amplification. Another reason for heterodyne processing is that for fixed fractional bandwidth, the instantaneous bandwidth increases linearly in frequency. This allows improved range resolution. The one notable exception to heterodyne (downconversion) radar systems is ultra-wideband radar. Here a single cycle, or transient wave, is used similar to UWB communications, see List of UWB channels.

Noise is random and target signals are not. Signal processing can take advantage of this phenomenon to reduce the noise floor using two strategies. The kind of signal integration used with Moving Target Indication can improve noise up to for each stage. The signal can also be split among multiple filters for pulse-Doppler signal processing, which reduces the noise floor by the number of filters. These improvements depend upon coherence.

Interference

Radar systems must overcome unwanted signals in order to focus only on the actual targets of interest. These unwanted signals may originate from internal and external sources, both passive and active. The ability of the radar system to overcome these unwanted signals defines its signal-to-noise ratio (SNR). SNR is defined as the ratio of a signal power to the noise power within the desired signal; it compares the level of a desired target signal to the level of background noise (atmospheric noise and noise generated within the receiver). The higher a system's SNR, the better it is in isolating actual targets from the surrounding noise signals.

Clutter

Clutter refers to radio frequency (RF) echoes returned from targets which are uninteresting to the radar operators. Such targets include natural objects such as ground, sea, precipitation (such as rain, snow or hail), sand storms, animals (especially birds), atmospheric turbulence, and other atmospheric effects, such as ionosphere reflections, meteor trails, and three body scatter spike. Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff.

Some clutter may also be caused by a long radar waveguide between the radar transceiver and the antenna. In a typical plan position indicator (PPI) radar with a rotating antenna, this will usually be seen as a "sun" or "sunburst" in the centre of the display as the receiver responds to echoes from dust particles and misguided RF in the waveguide. Adjusting the timing between when the transmitter sends a pulse and when the receiver stage is enabled will generally reduce the sunburst without affecting the accuracy of the range, since most sunburst is caused by a diffused transmit pulse reflected before it leaves the antenna. Clutter is considered a passive interference source, since it only appears in response to radar signals sent by the radar.

Clutter is detected and neutralized in several ways. Clutter tends to appear static between radar scans; on subsequent scan echoes, desirable targets will appear to move, and all stationary echoes can be eliminated. Sea clutter can be reduced by using horizontal polarization, while rain is reduced with circular polarization (note that meteorological radars wish for the opposite effect, and therefore use linear polarization to detect precipitation). Other methods attempt to increase the signal-to-clutter ratio.

Clutter moves with the wind or is stationary. Two common strategies to improve measure or performance in a clutter environment are:

Moving Target Indication, which integrates successive pulses and
Doppler processing, which uses filters to separate clutter from desirable signals.

Clutter may also originate from multipath echoes from valid targets caused by ground reflection, atmospheric ducting or ionospheric reflection/refraction (e.g., Anomalous propagation). This clutter type is especially bothersome since it appears to move and behave like other normal (point) targets of interest. In a typical scenario, an aircraft echo is reflected from the ground below, appearing to the receiver as an identical target below the correct one. The radar may try to unify the targets, reporting the target at an incorrect height, or eliminating it on the basis of jitter or a physical impossibility. Terrain bounce jamming exploits this response by amplifying the radar signal and directing it downward. These problems can be overcome by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below ground or above a certain height. Monopulse can be improved by altering the elevation algorithm used at low elevation. In newer air traffic control radar equipment, algorithms are used to identify the false targets by comparing the current pulse returns to those adjacent, as well as calculating return improbabilities.

Jamming

Radar jamming refers to radio frequency signals originating from sources outside the radar, transmitting in the radar's frequency and thereby masking targets of interest. Jamming may be intentional, as with an electronic warfare tactic, or unintentional, as with friendly forces operating equipment that transmits using the same frequency range. Jamming is considered an active interference source, since it is initiated by elements outside the radar and in general unrelated to the radar signals.

Jamming is problematic to radar since the jamming signal only needs to travel one way (from the jammer to the radar receiver) whereas the radar echoes travel two ways (radar-target-radar) and are therefore significantly reduced in power by the time they return to the radar receiver. Jammers therefore can be much less powerful than their jammed radars and still effectively mask targets along the line of sight from the jammer to the radar (mainlobe jamming). Jammers have an added effect of affecting radars along other lines of sight through the radar receiver's sidelobes (sidelobe jamming).

Mainlobe jamming can generally only be reduced by narrowing the mainlobe solid angle and cannot fully be eliminated when directly facing a jammer which uses the same frequency and polarization as the radar. Sidelobe jamming can be overcome by reducing receiving sidelobes in the radar antenna design and by using an omnidirectional antenna to detect and disregard non-mainlobe signals. Other anti-jamming techniques are frequency hopping and polarization.

Radar signal processing

Distance measurement

Transit time

One way to obtain a distance measurement is based on the time-of-flight: transmit a short pulse of radio signal (electromagnetic radiation) and measure the time it takes for the reflection to return. The distance is one-half the product of the round trip time (because the signal has to travel to the target and then back to the receiver) and the speed of the signal. Since radio waves travel at the speed of light, accurate distance measurement requires high-performance electronics. In most cases, the receiver does not detect the return while the signal is being transmitted. Through the use of a duplexer, the radar switches between transmitting and receiving at a predetermined rate. A similar effect imposes a maximum range as well. In order to maximize range, longer times between pulses should be used, referred to as a pulse repetition time, or its reciprocal, pulse repetition frequency.

These two effects tend to be at odds with each other, and it is not easy to combine both good short range and good long range in a single radar. This is because the short pulses needed for a good minimum range broadcast have less total energy, making the returns much smaller and the target harder to detect. This could be offset by using more pulses, but this would shorten the maximum range. So each radar uses a particular type of signal. Long-range radars tend to use long pulses with long delays between them, and short range radars use smaller pulses with less time between them. As electronics have improved many radars now can change their pulse repetition frequency, thereby changing their range. The newest radars fire two pulses during one cell, one for short range (10 km / 6 miles) and a separate signal for longer ranges (100 km /60 miles).

The distance resolution and the characteristics of the received signal as compared to noise depends on the shape of the pulse. The pulse is often modulated to achieve better performance using a technique known as pulse compression.

Distance may also be measured as a function of time. The radar mile is the amount of time it takes for a radar pulse to travel one nautical mile, reflect off a target, and return to the radar antenna. Since a nautical mile is defined as 1,852 meters, then dividing this distance by the speed of light (299,792,458 meters per second), and then multiplying the result by 2 yields a result of 12.36 microseconds in duration.

Frequency modulation

Another form of distance measuring radar is based on frequency modulation. Frequency comparison between two signals is considerably more accurate, even with older electronics, than timing the signal. By measuring the frequency of the returned signal and comparing that with the original, the difference can be easily measured.

This technique can be used in continuous wave radar and is often found in aircraft radar altimeters. In these systems a "carrier" radar signal is frequency modulated in a predictable way, typically varying up and down with a sine wave or sawtooth pattern at audio frequencies. The signal is then sent out from one antenna and received on another, typically located on the bottom of the aircraft, and the signal can be continuously compared using a simple beat frequency modulator that produces an audio frequency tone from the returned signal and a portion of the transmitted signal.

Since the signal frequency is changing, by the time the signal returns to the aircraft the transmit frequency has changed. The amount of frequency shift is used to measure distance.

The modulation index riding on the receive signal is proportional to the time delay between the radar and the reflector. The amount of that frequency shift becomes greater with greater time delay. The measure of the amount of frequency shift is directly proportional to the distance traveled. That distance can be displayed on an instrument, and it may also be available via the transponder. This signal processing is similar to that used in speed detecting Doppler radar. Example systems using this approach are AZUSA, MISTRAM, and UDOP.
A further advantage is that the radar can operate effectively at relatively low frequencies. This was important in the early development of this type when high frequency signal generation was difficult or expensive.

Terrestrial radar uses low-power FM signals that cover a larger frequency range. The multiple reflections are analyzed mathematically for pattern changes with multiple passes creating a computerized synthetic image. Doppler effects are used which allows slow moving objects to be detected as well as largely eliminating "noise" from the surfaces of bodies of water.

Speed measurement

Speed is the change in distance to an object with respect to time. Thus the existing system for measuring distance, combined with a memory capacity to see where the target last was, is enough to measure speed. At one time the memory consisted of a user making grease pencil marks on the radar screen and then calculating the speed using a slide rule. Modern radar systems perform the equivalent operation faster and more accurately using computers.

If the transmitter's output is coherent (phase synchronized), there is another effect that can be used to make almost instant speed measurements (no memory is required), known as the Doppler effect. Most modern radar systems use this principle into Doppler radar and pulse-Doppler radar systems (weather radar, military radar, etc...). The Doppler effect is only able to determine the relative speed of the target along the line of sight from the radar to the target. Any component of target velocity perpendicular to the line of sight cannot be determined by using the Doppler effect alone, but it can be determined by tracking the target's azimuth over time.

It is possible to make a Doppler radar without any pulsing, known as a continuous-wave radar (CW radar), by sending out a very pure signal of a known frequency. CW radar is ideal for determining the radial component of a target's velocity. CW radar is typically used by traffic enforcement to measure vehicle speed quickly and accurately where range is not important.

When using a pulsed radar, the variation between the phase of successive returns gives the distance the target has moved between pulses, and thus its speed can be calculated. Other mathematical developments in radar signal processing include time-frequency analysis (Weyl Heisenberg or wavelet), as well as the chirplet transform which makes use of the change of frequency of returns from moving targets ("chirp").

Pulse-Doppler signal processing

Pulse-Doppler signal processing includes frequency filtering in the detection process. The space between each transmit pulse is divided into range cells or range gates. Each cell is filtered independently much like the process used by a spectrum analyzer to produce the display showing different frequencies. Each different distance produces a different spectrum. These spectra are used to perform the detection process. This is required to achieve acceptable performance in hostile environments involving weather, terrain, and electronic countermeasures.

The primary purpose is to measure both the amplitude and frequency of the aggregate reflected signal from multiple distances. This is used with weather radar to measure radial wind velocity and precipitation rate in each different volume of air. This is linked with computing systems to produce a real-time electronic weather map. Aircraft safety depends upon continuous access to accurate weather radar information that is used to prevent injuries and accidents. Weather radar uses a low PRF. Coherency requirements are not as strict as those for military systems because individual signals ordinarily do not need to be separated. Less sophisticated filtering is required, and range ambiguity processing is not normally needed with weather radar in comparison with military radar intended to track air vehicles.

The alternate purpose is "look-down/shoot-down" capability required to improve military air combat survivability. Pulse-Doppler is also used for ground based surveillance radar required to defend personnel and vehicles. Pulse-Doppler signal processing increases the maximum detection distance using less radiation in close proximity to aircraft pilots, shipboard personnel, infantry, and artillery. Reflections from terrain, water, and weather produce signals much larger than aircraft and missiles, which allows fast moving vehicles to hide using nap-of-the-earth flying techniques and stealth technology to avoid detection until an attack vehicle is too close to destroy. Pulse-Doppler signal processing incorporates more sophisticated electronic filtering that safely eliminates this kind of weakness. This requires the use of medium pulse-repetition frequency with phase coherent hardware that has a large dynamic range. Military applications require medium PRF which prevents range from being determined directly, and range ambiguity resolution processing is required to identify the true range of all reflected signals. Radial movement is usually linked with Doppler frequency to produce a lock signal that cannot be produced by radar jamming signals. Pulse-Doppler signal processing also produces audible signals that can be used for threat identification.

Reduction of interference effects

Signal processing is employed in radar systems to reduce the radar interference effects. Signal processing techniques include moving target indication, Pulse-Doppler signal processing, moving target detection processors, correlation with secondary surveillance radar targets, space-time adaptive processing, and track-before-detect. Constant false alarm rate and digital terrain model processing are also used in clutter environments.

Plot and track extraction

Main article: Track_algorithm

A Track algorithm is a radar performance enhancement strategy. Tracking algorithms provide the ability to predict future position of multiple moving objects based on the history of the individual positions being reported by sensor systems.
Historical information is accumulated and used to predict future position for use with air traffic control, threat estimation, combat system doctrine, gun aiming, and missile guidance. Position data is accumulated radar sensors over the span of a few minutes.
There are four common track algorithms.

Nearest Neighbor
Probabilistic Data Association
Multiple Hypothesis Tracking
Interactive Multiple Model (IMM)

Radar video returns from aircraft can be subjected to a plot extraction process whereby spurious and interfering signals are discarded. A sequence of target returns can be monitored through a device known as a plot extractor.
The non-relevant real time returns can be removed from the displayed information and a single plot displayed. In some radar systems, or alternatively in the command and control system to which the radar is connected, a radar tracker is used to associate the sequence of plots belonging to individual targets and estimate the targets' headings and speeds.

Engineering

A radar's components are:

A transmitter that generates the radio signal with an oscillator such as a klystron or a magnetron and controls its duration by a modulator.
A waveguide that links the transmitter and the antenna.
A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations.
A receiver. Knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using a matched filter.
A display processor to produce signals for human readable output devices.
An electronic section that controls all those devices and the antenna to perform the radar scan ordered by software.
A link to end user devices and displays.

Antenna design

Radio signals broadcast from a single antenna will spread out in all directions, and likewise a single antenna will receive signals equally from all directions. This leaves the radar with the problem of deciding where the target object is located.

Early systems tended to use omnidirectional broadcast antennas, with directional receiver antennas which were pointed in various directions. For instance, the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display. The maximum return would be detected with an antenna at right angles to the target, and a minimum with the antenna pointed directly at it (end on). The operator could determine the direction to a target by rotating the antenna so one display showed a maximum while the other showed a minimum. One serious limitation with this type of solution is that the broadcast is sent out in all directions, so the amount of energy in the direction being examined is a small part of that transmitted. To get a reasonable amount of power on the "target", the transmitting aerial should also be directional.

Parabolic reflector

More modern systems use a steerable parabolic "dish" to create a tight broadcast beam, typically using the same dish as the receiver. Such systems often combine two radar frequencies in the same antenna in order to allow automatic steering, or radar lock.

Parabolic reflectors can be either symmetric parabolas or spoiled parabolas: Symmetric parabolic antennas produce a narrow "pencil" beam in both the X and Y dimensions and consequently have a higher gain. The NEXRAD Pulse-Doppler weather radar uses a symmetric antenna to perform detailed volumetric scans of the atmosphere. Spoiled parabolic antennas produce a narrow beam in one dimension and a relatively wide beam in the other. This feature is useful if target detection over a wide range of angles is more important than target location in three dimensions. Most 2D surveillance radars use a spoiled parabolic antenna with a narrow azimuthal beamwidth and wide vertical beamwidth. This beam configuration allows the radar operator to detect an aircraft at a specific azimuth but at an indeterminate height. Conversely, so-called "nodder" height finding radars use a dish with a narrow vertical beamwidth and wide azimuthal beamwidth to detect an aircraft at a specific height but with low azimuthal precision.

Types of scan

Primary Scan: A scanning technique where the main antenna aerial is moved to produce a scanning beam, examples include circular scan, sector scan, etc.
Secondary Scan: A scanning technique where the antenna feed is moved to produce a scanning beam, examples include conical scan, unidirectional sector scan, lobe switching, etc.
Palmer Scan: A scanning technique that produces a scanning beam by moving the main antenna and its feed. A Palmer Scan is a combination of a Primary Scan and a Secondary Scan.

Slotted waveguide

Applied similarly to the parabolic reflector, the slotted waveguide is moved mechanically to scan and is particularly suitable for non-tracking surface scan systems, where the vertical pattern may remain constant. Owing to its lower cost and less wind exposure, shipboard, airport surface, and harbour surveillance radars now use this approach in preference to a parabolic antenna.

Frequency bands

The traditional band names originated as code-names during World War II and are still in military and aviation use throughout the world. They have been adopted in the United States by the Institute of Electrical and Electronics Engineers and internationally by the International Telecommunication Union. Most countries have additional regulations to control which parts of each band are available for civilian or military use.

Other users of the radio spectrum, such as the broadcasting and electronic countermeasures industries, have replaced the traditional military designations with their own systems.

Radar frequency bands

Band name Frequency range Wavelength range Notes

HF

3–30 MHz 10–100 m Coastal radar systems, over-the-horizon radar (OTH) radars; 'high frequency'

P < 300 MHz 1 m+ 'P' for 'previous', applied retrospectively to early radar systems

VHF 30–300 MHz 1–10 m Very long range, ground penetrating; 'very high frequency'

UHF 300–1000 MHz 0.3–1 m Very long range (e.g. ballistic missile early warning), ground penetrating, foliage penetrating; 'ultra high frequency'

UWB 1.6–10.5 GHz 18.75 cm – 2.8 cm Used for through-the-wall radar and imaging systems.

L 1–2 GHz 15–30 cm Long range air traffic control and surveillance; 'L' for 'long'

S
2–4 GHz 7.5–15 cm Moderate range surveillance, Terminal air traffic control, long-range weather, marine radar; 'S' for 'short'

C
4–8 GHz 3.75–7.5 cm Satellite transponders; a compromise (hence 'C') between X and S bands; weather; long range tracking

X
8–12 GHz 2.5–3.75 cm
Missile guidance, marine radar, weather, medium-resolution mapping and ground surveillance; in the USA the narrow range 10.525 GHz ±25 MHz is used for airport radar; short range tracking. Named X band because the frequency was a secret during WW2.

K_u 12–18 GHz 1.67–2.5 cm High-resolution, also used for satellite transponders, frequency under K band (hence 'u')

K 18–24 GHz 1.11–1.67 cm From German kurz, meaning 'short'; limited use due to absorption by water vapour, so K_u and K_a were used instead for surveillance. K-band is used for detecting clouds by meteorologists, and by police for detecting speeding motorists. K-band radar guns operate at 24.150 ± 0.100 GHz.

K_a 24–40 GHz 0.75–1.11 cm
Mapping, short range, airport surveillance; frequency just above K band (hence 'a') Photo radar, used to trigger cameras which take pictures of license plates of cars running red lights, operates at 34.300 ± 0.100 GHz.

mm 40–300 GHz 7.5 mm – 1 mm Millimetre band, subdivided as below. The frequency ranges depend on waveguide size. Multiple letters are assigned to these bands by different groups. These are from Baytron, a now defunct company that made test equipment.

V 40–75 GHz 4.0–7.5 mm Very strongly absorbed by atmospheric oxygen, which resonates at 60 GHz.

W
75–110 GHz
2.7–4.0 mm

Used as a visual sensor for experimental autonomous vehicles, high-resolution meteorological observation, and imaging.

**Radar frequency bands**
Band name	Frequency range	Wavelength range	Notes
HF	3–30 MHz	10–100 m	Coastal radar systems, over-the-horizon radar (OTH) radars; 'high frequency'
P	< 300 MHz	1 m+	'P' for 'previous', applied retrospectively to early radar systems
VHF	30–300 MHz	1–10 m	Very long range, ground penetrating; 'very high frequency'
UHF	300–1000 MHz	0.3–1 m	Very long range (e.g. ballistic missile early warning), ground penetrating, foliage penetrating; 'ultra high frequency'
UWB	1.6–10.5 GHz	18.75 cm – 2.8 cm	Used for through-the-wall radar and imaging systems.
L	1–2 GHz	15–30 cm	Long range air traffic control and surveillance; 'L' for 'long'
S	2–4 GHz	7.5–15 cm	Moderate range surveillance, Terminal air traffic control, long-range weather, marine radar; 'S' for 'short'
C	4–8 GHz	3.75–7.5 cm	Satellite transponders; a compromise (hence 'C') between X and S bands; weather; long range tracking
X	8–12 GHz	2.5–3.75 cm	Missile guidance, marine radar, weather, medium-resolution mapping and ground surveillance; in the USA the narrow range 10.525 GHz ±25 MHz is used for airport radar; short range tracking. Named X band because the frequency was a secret during WW2.
K_u	12–18 GHz	1.67–2.5 cm	High-resolution, also used for satellite transponders, frequency under K band (hence 'u')
K	18–24 GHz	1.11–1.67 cm	From German kurz, meaning 'short'; limited use due to absorption by water vapour, so K_u and K_a were used instead for surveillance. K-band is used for detecting clouds by meteorologists, and by police for detecting speeding motorists. K-band radar guns operate at 24.150 ± 0.100 GHz.
K_a	24–40 GHz	0.75–1.11 cm	Mapping, short range, airport surveillance; frequency just above K band (hence 'a') Photo radar, used to trigger cameras which take pictures of license plates of cars running red lights, operates at 34.300 ± 0.100 GHz.
mm	40–300 GHz	7.5 mm – 1 mm	Millimetre band, subdivided as below. The frequency ranges depend on waveguide size. Multiple letters are assigned to these bands by different groups. These are from Baytron, a now defunct company that made test equipment.
V	40–75 GHz	4.0–7.5 mm	Very strongly absorbed by atmospheric oxygen, which resonates at 60 GHz.
W	75–110 GHz	2.7–4.0 mm	Used as a visual sensor for experimental autonomous vehicles, high-resolution meteorological observation, and imaging.

Radar modulators

Modulators act to provide the waveform of the RF-pulse. There are two different radar modulator designs:

High voltage switch for non-coherent keyed power-oscillators These modulators consist of a high voltage pulse generator formed from a high voltage supply, a pulse forming network, and a high voltage switch such as a thyratron. They generate short pulses of power to feed, e.g., the magnetron, a special type of vacuum tube that converts DC (usually pulsed) into microwaves. This technology is known as pulsed power. In this way, the transmitted pulse of RF radiation is kept to a defined and usually very short duration.
Hybrid mixers, fed by a waveform generator and an exciter for a complex but coherent waveform. This waveform can be generated by low power/low-voltage input signals. In this case the radar transmitter must be a power-amplifier, e.g., a klystron tube or a solid state transmitter. In this way, the transmitted pulse is intrapulse-modulated and the radar receiver must use pulse compression techniques.

Radar coolant

Coolanol (silicate ester) was used in several military radars in the 1970s. However, it is hygroscopic, leading to formation of highly flammable alcohol. The loss of a U.S. Navy aircraft in 1978 was attributed to a silicate ester fire. Coolanol is also expensive and toxic. The U.S. Navy has instituted a program named Pollution Prevention (P2) to reduce or eliminate the volume and toxicity of waste, air emissions, and effluent discharges. Because of this, Coolanol is used less often today.

Coherent microwave amplifiers operating above 1,000 watts microwave output, like traveling wave tubes and klystrons, require liquid coolant. The electron beam must contain 5 to 10 times more power than the microwave output, which can produce enough heat to corrupt the vacuum with plasma. This flows from the collector toward the cathode. Magnetic focusing for the electron beam forces ionized gas atoms into the same location as the electron beam. Plasma ions flow in the opposite direction of the electron beam. This introduces FM modulation, and that degrades Doppler performance. Liquid coolant with minimum pressure and flow rate is required to control collector gassing, and deionized water is normally used with most high power surface radar systems that utilize Doppler processing.

Orbit Downloader

2014-01-18T22:17:00.000+05:30

Orbit Downloader

Orbit Downloader is a free Internet download manager that is focusing on improving your overall download experience but also downloading videos, music or files from streaming websites such as YT, MySpace, RapidShare, Pandora and others. Orbit Downloader’s interface was designed to be user friendly but also contains a large number of features to satisfy both beginners and power users.

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Orbit Downloader is licensed as Freeware for the Windows operating system / platform. Orbit Downloader is provided as a free download for all software users (Freeware).

This download is managed by our ad-supported smart download manager. During the download process we may show commercial offers, such as a toolbar or other browser add-ons. The download manager does not have any relationship with the author of this product. The product can be downloaded as well freely from the author's website. You are not obligated to install commercial offer during the process of install

All of the downloads on our website are completely free and are thoroughly reviewed to make sure they are virus free. We use a smart download manager to manage all the downloads initiated from this website.
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Transformer

2013-12-26T20:55:00.000+05:30

Transformer

A transformer is a static electrical device that transfers energy by inductive coupling between its winding circuits. A varying current in the primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic flux through the secondary winding. This varying magnetic flux induces a varying electromotive force (emf) or voltage in the secondary winding. Transformers can be used to vary the relative voltage of circuits or isolate them, or both.

Transformers range in size from thumbnail-sized used in microphones to units weighing hundreds of tons interconnecting the power grid. A wide range of transformer designs are used in electronic and electric power applications. Transformers are essential for the transmission, distribution, and utilization of electrical energy.

Basic principles

The ideal transformer

The ideal condition assumptions are:

The windings of the transformer have negligible resistance thus there is no copper losses in the winding, no voltage drop
Flux is confined within the core. Therefore, it is the same flux that links both the windings
Permeability of the core is infinitely high which implies that a very small mmf (current) is required to set up the flux
The core does not incur any hysteresis or eddy current loss. Hence, no core losses

Consider the ideal, lossless, perfectly-coupled transformer shown in the circuit diagram at right having primary and secondary windings with N_P and N_S turns, respectively.

The ideal transformer induces secondary voltage E_S =V_S as a proportion of the primary voltage V_P = E_P and respective winding turns as given by the equation

where,

- V_P/V_S = E_P/E_S = a is the voltage ratio and N_P/N_S = a is the winding turns ratio, the value of these ratios being respectively higher and lower than unity for step-down and step-up transformers,

- V_P designates source impressed voltage,

- V_S designates output voltage, and,

- E_P & E_S designate respective emf induced voltages.

Any load impedance connected to the ideal transformer's secondary winding causes current to flow without losses from primary to secondary circuits, the resulting input and output apparent power therefore being equal as given by the equation

Combining the two equations yields the following ideal transformer identity

This formula is a reasonable approximation for the typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio.
The load impedance is defined in terms of secondary circuit voltage and current as follows

The apparent impedance of this secondary circuit load referred to the primary winding circuit is governed by a squared turns ratio multiplication factor relationship derived as follows

Induction law

The transformer is based on two principles: first, that an electric current can produce a magnetic field and second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.
Referring to the two figures here, current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, usually iron, so that most of the magnetic flux passes through both the primary and secondary coils. Any secondary winding connected load causes current and voltage induction from primary to secondary circuits in indicated directions.
The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that:

where V_s = E_s is the instantaneous voltage, N_s is the number of turns in the secondary coil, and dΦ/dt is the derivative of the magnetic flux Φ through one turn of the coil. If the turns of the coil are oriented perpendicularly to the magnetic field lines, the flux is the product of the magnetic flux density B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals

Taking the ratio of the above two equations gives the same voltage ratio and turns ratio relationship shown above, that is,

The changing magnetic field induces an emf across each winding. The primary emf, acting as it does in opposition to the primary voltage, is sometimes termed the counter emf. This is in accordance with Lenz's law, which states that induction of emf always opposes development of any such change in magnetic field.
As still lossless and perfectly-coupled, the transformer still behaves as described above in the ideal transformer.

Polarity

A dot convention is often used in transformer circuit diagrams, nameplates or terminal markings to define the relative polarity of transformer windings. Positively-increasing instantaneous current entering the primary winding's dot end induces positive polarity voltage at the secondary winding's dot end.

The real transformer

Real transformer deviations from ideal

The ideal model neglects the following basic linear aspects in real transformers: Core losses collectively called magnetizing current losses consisting of:

Hysteresis losses due to nonlinear application of the voltage applied in the transformer core
Eddy current losses due to joule heating in core proportional to the square of the transformer's applied voltage.
Whereas the ideal windings have no impedance, the windings in a real transformer have finite non-zero impedances in the form of:

Joule losses due to resistance in the primary and secondary windings

Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance.

Leakage flux

The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings. Such flux is termed leakage flux, and results in leakage inductance in series with the mutually coupled transformer windings. Leakage flux results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not directly a power loss (see Stray losses below), but results in inferior voltage regulation, causing the secondary voltage not to be directly proportional to the primary voltage, particularly under heavy load. Transformers are therefore normally designed to have very low leakage inductance. Nevertheless, it is impossible to eliminate all leakage flux because it plays an essential part in the operation of the transformer. The combined effect of the leakage flux and the electric field around the windings is what transfers energy from the primary to the secondary.
In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic bypass shunts may deliberately be introduced in a transformer design to limit the short-circuit current it will supply. Leaky transformers may be used to supply loads that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs or for safely handling loads that become periodically short-circuited such as electric arc welders.
Air gaps are also used to keep a transformer from saturating, especially audio-frequency transformers in circuits that have a DC component flowing in the windings.
Knowledge of leakage inductance is also useful when transformers are operated in parallel. It can be shown that if the percent impedance (Z) and associated winding leakage reactance-to-resistance (X/R) ratio of two transformers were hypothetically exactly the same, the transformers would share power in proportion to their respective volt-ampere ratings (e.g. 500 kVA unit in parallel with 1,000 kVA unit, the larger unit would carry twice the current). However, the impedance tolerances of commercial transformers are significant. Also, the Z impedance and X/R ratio of different capacity transformers tends to vary, corresponding 1,000 kVA and 500 kVA units' values being, to illustrate, respectively, Z ~ 5.75%, X/R ~ 3.75 and Z ~ 5%, X/R ~ 4.75.

Equivalent circuit

Referring to the diagram, a practical transformer's physical behavior may be represented by an equivalent circuit model, which can incorporate an ideal transformer.
Winding joule losses and leakage reactances are represented by the following series loop impedances of the model:

Primary winding: R_P, X_P

Secondary winding: R_S, X_S.

In normal course of circuit equivalence transformation, R_S and X_S are in practice usually referred to the primary side by multiplying these impedances by the turns ratio squared, (N_P/N_S)² = a².
Core loss and reactance is represented by the following shunt leg impedances of the model:

Core or iron losses: R_C

Magnetizing reactance: X_M.

R_C and X_M are collectively termed the magnetizing branch of the model.
Core losses are caused mostly by hysteresis and eddy current effects in the core and are proportional to the square of the core flux for operation at a given frequency. The finite permeability core requires a magnetizing current I_M to maintain mutual flux in the core. Magnetizing current is in phase with the flux, the relationship between the two being non-linear due to saturation effects. However, all impedances of the equivalent circuit shown are by definition linear and such non-linearity effects are not typically reflected in transformer equivalent circuits. With sinusoidal supply, core flux lags the induced emf by 90°. With open-circuited secondary winding, magnetizing branch current I₀ equals transformer no-load current.
The resulting model, though sometimes termed 'exact' equivalent circuit based on linearity assumptions, retains a number of approximations. Analysis may be simplified by assuming that magnetizing branch impedance is relatively high and relocating the branch to the left of the primary impedances. This introduces error but allows combination of primary and referred secondary resistances and reactances by simple summation as two series impedances.
Transformer equivalent circuit impedance and transformer ratio parameters can be derived from the following tests: Open-circuit test, short-circuit test, winding resistance test, and transformer ratio test.

Basic transformer parameters and construction

Effect of frequency

The time-derivative term in Faraday's Law shows that the flux in the core is the integral with respect to time of the applied voltage. Hypothetically an ideal transformer would work with direct-current excitation, with the core flux increasing linearly with time. In practice, the flux rises to the point where magnetic saturation of the core occurs, causing a large increase in the magnetizing current and overheating the transformer. All practical transformers must therefore operate with alternating (or pulsed direct) current.
The emf of a transformer at a given flux density increases with frequency. By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance. However, properties such as core loss and conductor skin effect also increase with frequency. Aircraft and military equipment employ 400 Hz power supplies which reduce core and winding weight. Conversely, frequencies used for some railway electrification systems were much lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50 – 60 Hz) for historical reasons concerned mainly with the limitations of early electric traction motors. As such, the transformers used to step-down the high over-head line voltages (e.g. 15 kV) were much heavier for the same power rating than those designed only for the higher frequencies.

Power transformer over-excitation condition caused by decreased frequency; flux (green), iron core's magnetic characteristics (red) and magnetizing current (blue).

Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current. At a lower frequency, the magnetizing current will increase. Operation of a transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. For example, transformers may need to be equipped with 'volts per hertz' over-excitation relays to protect the transformer from overvoltage at higher than rated frequency.
One example of state-of-the-art design is traction transformers used for electric multiple unit and high speed train service operating across the,country border and using different electrical standards, such transformers' being restricted to be positioned below the passenger compartment. The power supply to, and converter equipment being supply by, such traction transformers have to accommodate different input frequencies and voltage (ranging from as high as 50 Hz down to 16.7 Hz and rated up to 25 kV) while being suitable for multiple AC asynchronous motor and DC converters & motors with varying harmonics mitigation filtering requirements.
Large power transformers are vulnerable to insulation failure due to transient voltages with high-frequency components, such as caused in switching or by lightning.

Energy losses

An ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%.
Experimental transformers using superconducting windings achieve efficiencies of 99.85%. The increase in efficiency can save considerable energy, and hence money, in a large heavily loaded transformer; the trade-off is in the additional initial and running cost of the superconducting design.
As transformer losses vary with load, it is often useful to express these losses in terms of no-load loss, full-load loss, half-load loss, and so on. Hysteresis and eddy current losses are constant at all loads and dominate overwhelmingly at no-load, variable winding joule losses dominating increasingly as load increases. The no-load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply and a running cost. Designing transformers for lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost so that there is a trade-off between initial cost and running cost (also see energy efficient transformer).
Transformer losses arise from:

Winding joule losses

Current flowing through winding conductors causes joule heating. As frequency increases, skin effect and proximity effect causes winding resistance and, hence, losses to increase.

Core losses

Hysteresis losses

Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. According to Steinmetz's formula, the heat energy due to hysteresis is given by

, and,

hysteresis loss is thus given by

where, f is the frequency, η is the hysteresis coefficient and β_max is the maximum flux density, the empirical exponent of which varies from about 1.4 to 1 .8 but is often given as 1.6 for iron.

Eddy current losses

Ferromagnetic materials are also good conductors and a core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness. Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block; all transformers operating at low frequencies use laminated or similar cores.

Magnetostriction related transformer hum: Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction, the frictional energy of which produces an audible noise known as mains hum or transformer hum. This transformer hum is especially objectionable in transformers supplied at power frequencies and in high-frequency flyback transformers associated with PAL system CRTs.
Stray losses: Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat. There are also radiative losses due to the oscillating magnetic field but these are usually small.

Mechanical vibration and audible noise transmission: In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the primary and secondary windings. This energy incites vibration transmission in interconnected metalwork, thus amplifying audible transformer hum.

Core form and shell form transformers

Closed-core transformers are constructed in 'core form' or 'shell form'. When windings surround the core, the transformer is core form; when windings are surrounded by the core, the transformer is shell form. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils. Core form design tends to, as a general rule, be more economical, and therefore more prevalent, than shell form design for high voltage power transformer applications at the lower end of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or 75 MVA). At higher voltage and power ratings, shell form transformers tend to be more prevalent. Shell form design tends to be preferred for extra high voltage and higher MVA applications because, though more labor intensive to manufacture, shell form transformers are characterized as having inherently better kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit damage.

Construction

Cores

Laminated steel cores

Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel. The steel has a permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current and confine the flux to a path which closely couples the windings. Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires. Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation. The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation.
The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude. Thinner laminations reduce losses, but are more laborious and expensive to construct. Thin laminations are generally used on high-frequency transformers, with some of very thin steel laminations able to operate up to 10 kHz.
One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces, leading to its name of 'E-I transformer'. Such a design tends to exhibit more losses, but is very economical to manufacture. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. It is then cut in two, forming two C shapes, and the core assembled by binding the two C halves together with a steel strap. They have the advantage that the flux is always oriented parallel to the metal grains, reducing reluctance.
A steel core's remanence means that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform. Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to pass. On transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices.
Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel or amorphous (non-crystalline) metal alloy. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load.

Solid cores

Powdered iron cores are used in circuits such as switch-mode power supplies that operate above mains frequencies and up to a few tens of kilohertz. These materials combine high magnetic permeability with high bulk electrical resistivity. For frequencies extending beyond the VHF band, cores made from non-conductive magnetic ceramic materials called ferrites are common. Some radio-frequency transformers also have movable cores (sometimes called 'slugs') which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits.

Toroidal cores

Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or permalloy wound into a coil, powdered iron, or ferrite. A strip construction ensures that the grain boundaries are optimally aligned, improving the transformer's efficiency by reducing the core's reluctance. The closed ring shape eliminates air gaps inherent in the construction of an E-I core. The cross-section of the ring is usually square or rectangular, but more expensive cores with circular cross-sections are also available. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimizes the length of wire needed, and also provides screening to minimize the core's magnetic field from generating electromagnetic interference.
Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are higher cost and limited power capacity (see Classification parameters below). Because of the lack of a residual gap in the magnetic path, toroidal transformers also tend to exhibit higher inrush current, compared to laminated E-I types.
Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of inductive components. A drawback of toroidal transformer construction is the higher labor cost of winding. This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil. As a consequence, toroidal transformers rated more than a few kVA are uncommon. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings.

Air cores

A physical core is not an absolute requisite and a functioning transformer can be produced simply by placing the windings near each other, an arrangement termed an 'air-core' transformer. The air which comprises the magnetic circuit is essentially lossless, and so an air-core transformer eliminates loss due to hysteresis in the core material. The leakage inductance is inevitably high, resulting in very poor regulation, and so such designs are unsuitable for use in power distribution. They have however very high bandwidth, and are frequently employed in radio-frequency applications, for which a satisfactory coupling coefficient is maintained by carefully overlapping the primary and secondary windings. They're also used for resonant transformers such as Tesla coils where they can achieve reasonably low loss in spite of the high leakage inductance.

Windings

The conducting material used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn. For small power and signal transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from enamelled magnet wire, such as Formvar wire. Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard.High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braided Litz wire to minimize the skin-effect and proximity effect losses. Large power transformers use multiple-stranded conductors as well, since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings. Each strand is individually insulated, and the strands are arranged so that at certain points in the winding, or throughout the whole winding, each portion occupies different relative positions in the complete conductor. The transposition equalizes the current flowing in each strand of the conductor, and reduces eddy current losses in the winding itself. The stranded conductor is also more flexible than a solid conductor of similar size, aiding manufacture.
The windings of signal transformers minimize leakage inductance and stray capacitance to improve high-frequency response. Coils are split into sections, and those sections interleaved between the sections of the other winding.
Power-frequency transformers may have taps at intermediate points on the winding, usually on the higher voltage winding side, for voltage adjustment. Taps may be manually reconnected, or a manual or automatic switch may be provided for changing taps. Automatic on-load tap changers are used in electric power transmission or distribution, on equipment such as arc furnace transformers, or for automatic voltage regulators for sensitive loads. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit. Modulation transformers in AM transmitters are very similar.
Dry-type transformer winding insulation systems can be either of standard open-wound 'dip-and-bake' construction or of higher quality designs that include vacuum pressure impregnation (VPI), vacuum pressure encapsulation (VPE), and cast coil encapsulation processes. In the VPI process, a combination of heat, vacuum and pressure is used to thoroughly seal, bind, and eliminate entrained air voids in the winding polyester resin insulation coat layer, thus increasing resistance to corona. VPE windings are similar to VPI windings but provide more protection against environmental effects, such as from water, dirt or corrosive ambients, by multiple dips including typically in terms of final epoxy coat.

Cooling

To place the cooling problem in perspective, the accepted rule of thumb is that the life expectancy of insulation in all electric machines including all transformers is halved for about every 7°C to 10°C increase in operating temperature, this life expectancy halving rule holding more narrowly when the increase is between about 7°C to 8°C in the case of transformer winding cellulose insulation.
Small dry-type and liquid-immersed transformers are often self-cooled by natural convection and radiation heat dissipation. As power ratings increase, transformers are often cooled by forced-air cooling, forced-oil cooling, water-cooling, or combinations of these. Large transformers are filled with transformer oil that both cools and insulates the windings. Transformer oil is a highly refined mineral oil that cools the windings and insulation by circulating within the transformer tank. The mineral oil and paper insulation system has been extensively studied and used for more than 100 years. It is estimated that 50% of power transformers will survive 50 years of use, that the average age of failure of power transformers is about 10 to 15 years, and that about 30% of power transformer failures are due to insulation and overloading failures. Prolonged operation at elevated temperature degrades insulating properties of winding insulation and dielectric coolant, which not only shortens transformer life but can ultimately lead to catastrophic transformer failure. With a great body of empirical study as a guide, transformer oil testing including dissolved gas analysis provides valuable maintenance information. This can translate in a need to monitor, model, forecast and manage oil and winding conductor insulation temperature conditions under varying, possibly difficult, power loading conditions.
Building regulations in many jurisdictions require indoor liquid-filled transformers to either use dielectric fluids that are less flammable than oil, or be installed in fire-resistant rooms. Air-cooled dry transformers can be more economical where they eliminate the cost of a fire-resistant transformer room.
The tank of liquid filled transformers often has radiators through which the liquid coolant circulates by natural convection or fins. Some large transformers employ electric fans for forced-air cooling, pumps for forced-liquid cooling, or have heat exchangers for water-cooling. An oil-immersed transformer may be equipped with a Buchholz relay, which, depending on severity of gas accumulation due to internal arcing, is used to either alarm or de-energize the transformer. Oil-immersed transformer installations usually include fire protection measures such as walls, oil containment, and fire-suppression sprinkler systems. Another protection means consists in fast depressurization systems which are activated by the first dynamic pressure peak of the shock wave, avoiding transformer explosion before static pressure increases. Many explosions are reported to have been avoided thanks to this technology.
Polychlorinated biphenyls have properties that once favored their use as a dielectric coolant, though concerns over their environmental persistence led to a widespread ban on their use. Today, non-toxic, stable silicone-based oils, or fluorinated hydrocarbons may be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault. PCBs for new equipment was banned in 1981 and in 2000 for use in existing equipment in United Kingdom Legislation enacted in Canada between 1977 and 1985 essentially bans PCB use in transformers manufactured in or imported into the country after 1980, the maximum allowable level of PCB contamination in existing mineral oil transformers being 50 ppm.
Some transformers, instead of being liquid-filled, have their windings enclosed in sealed, pressurized tanks and cooled by nitrogen or sulfur hexafluoride gas.
Experimental power transformers in the 500-to-1,000 kVA range have been built with liquid nitrogen or helium cooled superconducting windings, which, compared to usual transformer losses, eliminates winding losses without affecting core losses.

Insulation drying

Construction of oil-filled transformers requires that the insulation covering the windings be thoroughly dried of residual moisture before the oil is introduced. Drying is carried out at the factory, and may also be required as a field service. Drying may be done by circulating hot air around the core, or by vapor-phase drying (VPD) where an evaporated solvent transfers heat by condensation on the coil and core.
For small transformers, resistance heating by injection of current into the windings is used. The heating can be controlled very well, and it is energy efficient. The method is called low-frequency heating (LFH) since the current is injected at a much lower frequency than the nominal of the power grid, which is normally 50 or 60 Hz. A lower frequency reduces the effect of the inductance in the transformer, so the voltage needed to induce the current can be reduced. The LFH drying method is also used for service of older transformers.

Bushings

Larger transformers are provided with high-voltage insulated bushings made of polymers or porcelain. A large bushing can be a complex structure since it must provide careful control of the electric field gradient without letting the transformer leak oil.

Classification parameters

Transformers can be classified in many ways, such as the following:

Power capacity: From a fraction of a volt-ampere (VA) to over a thousand MVA.
Duty of a transformer: Continuous, short-time, intermittent, periodic, varying.
Frequency range: Power-frequency, audio-frequency, or radio-frequency.
Voltage class: From a few volts to hundreds of kilovolts.
Cooling type: Dry and liquid-immersed - self-cooled, forced air-cooled; liquid-immersed - forced oil-cooled, water-cooled.
Circuit application: Such as power supply, impedance matching, output voltage and current stabilizer or circuit isolation.
Utilization: Pulse, power, distribution, rectifier, arc furnace, amplifier output, etc..
Basic magnetic form: Core form, shell form.
Constant-potential transformer descriptor: Step-up, step-down, isolation.
General winding configuration: By EIC vector group - various possible two-winding combinations of the phase designations delta, wye or star, and zigzag or interconnected star;
other - autotransformer, Scott-T, zigzag grounding transformer winding.
Rectifier phase-shift winding configuration: 2-winding, 6-pulse; 3-winding, 12-pulse; . . . n-winding, [n-1]*6-pulse; polygon; etc..

Types

For more details, see Transformer types or specific main articles, as shown.
A wide variety of transformer designs are used for different applications, though they share several common features. Important common transformer types include:

Autotransformer: Transformer in which part of the winding is common to both primary and secondary circuits.
Capacitor voltage transformer: Transformer in which capacitor divider is used to reduce high voltage before application to the primary winding.
Distribution transformer, power transformer: International standards make a distinction in terms of distribution transformers being used to distribute energy from transmission lines and networks for local consumption and power transformers being used to transfer electric energy between the generator and distribution primary circuits.
Phase angle regulating transformer: A specialised transformer used to control the flow of real power on three-phase electricity transmission networks.
Scott-T transformer: Transformer used for phase transformation from three-phase to two-phase and vice versa.
Polyphase transformer: Any transformer with more than one phase.
Grounding transformer: Transformer used for grounding three-phase circuits to create a neutral in a three wire system, using a wye-delta transformer, or more commonly, a zigzag grounding winding.
Leakage transformer: Transformer that has loosely coupled windings.
Resonant transformer: Transformer that uses resonance to generate a high secondary voltage.
Audio transformer: Transformer used in audio equipment.
Output transformer: Transformer used to match the output of a valve amplifier to its load.
Instrument transformer: Potential or current transformer used to accurately and safely represent voltage, current or phase position of high voltage or high power circuits.

Flip-flop

2013-12-24T09:13:00.001+05:30

Flip-flop

In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. A flip-flop is a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Flip-flops and latches are a fundamental building block of digital electronics systems used in computers, communications, and many other types of systems.

Flip-flops and latches are used as data storage elements. Such data storage can be used for storage of state, and such a circuit is described as sequential logic. When used in a finite-state machine, the output and next state depend not only on its current input, but also on its current state (and hence, previous inputs). It can also be used for counting of pulses, and for synchronizing variably-timed input signals to some reference timing signal.

Flip-flops can be either simple (transparent or opaque) or clocked (synchronous or edge-triggered); the simple ones are commonly called latches. The word latch is mainly used for storage elements, while clocked devices are described as flip-flops. A latch is level-sensitive, whereas a flip-flop is edge-sensitive. That is, when a latch is enabled it becomes transparent, while a flip flop's output only changes on a single type (positive going or negative going) of clock edge.

History

The first electronic flip-flop was invented in 1918 by William Eccles and F. W. Jordan. It was initially called the Eccles–Jordan trigger circuit and consisted of two active elements (vacuum tubes). Such circuits and their transistorized versions were common in computers even after the introduction of integrated circuits, though flip-flops made from logic gates are also common now. Early flip-flops were known variously as trigger circuits or multivibrators.

According to P. L. Lindley, a JPL engineer, the flip-flop types discussed below (RS, D, T, JK) were first discussed in a 1954 UCLA course on computer design by Montgomery Phister, and then appeared in his book Logical Design of Digital Computers. Lindley was at the time working at Hughes Aircraft under Dr. Eldred Nelson, who had coined the term JK for a flip-flop which changed states when both inputs were on. The other names were coined by Phister. They differ slightly from some of the definitions given below. Lindley explains that he heard the story of the JK flip-flop from Dr. Eldred Nelson, who is responsible for coining the term while working at Hughes Aircraft. Flip-flops in use at Hughes at the time were all of the type that came to be known as J-K. In designing a logical system, Dr. Nelson assigned letters to flip-flop inputs as follows: #1: A & B, #2: C & D, #3: E & F, #4: G & H, #5: J & K. Nelson used the notations "j-input" and "k-input" in a patent application filed in 1953.

Implementation

Flip-flops can be either simple (transparent or asynchronous) or clocked (synchronous); the transparent ones are commonly called latches. The word latch is mainly used for storage elements, while clocked devices are described as flip-flops.
Simple flip-flops can be built around a pair of cross-coupled inverting elements: vacuum tubes, bipolar transistors, field effect transistors, inverters, and inverting logic gates have all been used in practical circuits. Clocked devices are specially designed for synchronous systems; such devices ignore their inputs except at the transition of a dedicated clock signal (known as clocking, pulsing, or strobing). Clocking causes the flip-flop to either change or retain its output signal based upon the values of the input signals at the transition. Some flip-flops change output on the rising edge of the clock, others on the falling edge.

Since the elementary amplifying stages are inverting, two stages can be connected in succession (as a cascade) to form the needed non-inverting amplifier. In this configuration, each amplifier may be considered as an active inverting feedback network for the other inverting amplifier. Thus the two stages are connected in a non-inverting loop although the circuit diagram is usually drawn as a symmetric cross-coupled pair (both the drawings are initially introduced in the Eccles–Jordan patent).

Flip-flop types

Flip-flops can be divided into common types: the SR ("set-reset"), D ("data" or "delay"), T ("toggle"), and JK types are the common ones. The behavior of a particular type can be described by what is termed the characteristic equation, which derives the "next" (i.e., after the next clock pulse) output,

Q next

in terms of the input signal(s) and/or the current output, .

Simple set-reset latches

SR NOR latch

An SR latch, constructed from a pair of cross-coupled NOR gates (an animated picture). Red and black mean logical '1' and '0', respectively.

When using static gates as building blocks, the most fundamental latch is the simple SR latch, where S and R stand for set and reset. It can be constructed from a pair of cross-coupled NOR logic gates. The stored bit is present on the output marked Q.

While the S and R inputs are both low, feedback maintains the Q and Q outputs in a constant state, with Q the complement of Q. If S (Set) is pulsed high while R (Reset) is held low, then the Q output is forced high, and stays high when S returns to low; similarly, if R is pulsed high while S is held low, then the Q output is forced low, and stays low when R returns to low.

The R = S = 1 combination is called a restricted combination or a forbidden state because, as both NOR gates then output zeros, it breaks the logical equation Q = not Q. The combination is also inappropriate in circuits where both inputs may go low simultaneously (i.e. a transition from restricted to keep). The output would lock at either 1 or 0 depending on the propagation time relations between the gates (a race condition).
To overcome the restricted combination, one can add gates to the inputs that would convert (S,R) = (1,1) to one of the non-restricted combinations. That can be:

Q = 1 (1,0) – referred to as an S (dominated)-latch
Q = 0 (0,1) – referred to as an R (dominated)-latch

This is done in nearly every Programmable logic controller.

Keep state (0,0) – referred to as an E-latch

Alternatively, the restricted combination can be made to toggle the output. The result is the JK latch.
Characteristic: Q+ = R'Q + R'S or Q+ = R'Q + S.

SR NAND latch

An SR latch

This is an alternate model of the simple SR latch which is built with NAND logic gates. Set and reset now become active low signals, denoted S and R respectively. Otherwise, operation is identical to that of the SR latch. Historically, SR-latches have been predominant despite the notational inconvenience of active-low inputs.

SR latch operation
S	R	Action
0	0	Restricted combination
0	1	Q = 1
1	0	Q = 0
1	1	No Change

Symbol for an SR NAND latch

JK latch

The JK latch is much less frequently used than the JK flip-flop. The JK latch follows the following state table:

JK latch truth table
J	K	Q_next	Comment
0	0	Q	No change
0	1	0	Reset
1	0	1	Set
1	1	Q	Toggle

Hence, the JK latch is an SR latch that is made to toggle its output when passed the restricted combination of 11. Unlike the JK flip-flop, the 11 input combination for the SR latch is not useful because there is no clock that directs toggling.

Gated latches and conditional transparency

Latches are designed to be transparent. That is, input signal changes cause immediate changes in output; when several transparent latches follow each other, using the same enable signal, signals can propagate through all of them at once. Alternatively, additional logic can be added to a simple transparent latch to make it non-transparent or opaque when another input (an "enable" input) is not asserted. By following a transparent-high latch with a transparent-low (or opaque-high) latch, a master–slave flip-flop is implemented.

Gated SR latch

A synchronous SR latch (sometimes clocked SR flip-flop) can be made by adding a second level of NAND gates to the inverted SR latch (or a second level of AND gates to the direct SR latch). The extra gates further invert the inputs so the simple SR latch becomes a gated SR latch (and a simple SR latch would transform into a gated SR latch with inverted enable).

With E high (enable true), the signals can pass through the input gates to the encapsulated latch; all signal combinations except for (0,0) = hold then immediately reproduce on the (Q,Q) output, i.e. the latch is transparent.

With E low (enable false) the latch is closed (opaque) and remains in the state it was left the last time E was high.

The enable input is sometimes a clock signal, but more often a read or write strobe.

Metastability

Flip-flops are subject to a problem called metastability, which can happen when two inputs, such as data and clock or clock and reset, are changing at about the same time. When the order is not clear, within appropriate timing constraints, the result is that the output may behave unpredictably, taking many times longer than normal to settle to one state or the other, or even oscillating several times before settling. Theoretically, the time to settle down is not bounded. In a computer system, this metastability can cause corruption of data or a program crash, if the state is not stable before another circuit uses its value; in particular, if two different logical paths use the output of a flip-flop, one path can interpret it as a 0 and the other as a 1 when it has not resolved to stable state, putting the machine into an inconsistent state.

Timing considerations

Setup, hold, recovery, removal times

Setup time is the minimum amount of time the data signal should be held steady before the clock event so that the data are reliably sampled by the clock. This applies to synchronous input signals to the flip-flop.
Hold time is the minimum amount of time the data signal should be held steady after the clock event so that the data are reliably sampled. This applies to synchronous input signals to the flip-flop.
Synchronous signals (like Data) should be held steady from the set-up time to the hold time, where both times are relative to the clock signal.

Recovery time is like setup time for asynchronous ports (set, reset). It is the time available between the asynchronous signals going inactive and the active clock edge.
Removal time is like hold time for asynchronous ports (set, reset). It is the time between active clock edge and asynchronous signal going inactive.

Short impulses applied to asynchronous inputs (set, reset) should not be applied completely within the recovery-removal period, or else it becomes entirely indeterminable whether the flip-flop will transition to the appropriate state. In another case, where an asynchronous signal simply makes one transition that happens to fall between the recovery/removal time, eventually the asynchronous signal will be applied, but in that case it is also possible that a very short glitch may appear on the output, dependent on the synchronous input signal. This second situation may or may not have significance to a circuit design.
Set and Reset (and other) signals may be either synchronous or asynchronous and therefore may be characterized with either Setup/Hold or Recovery/Removal times, and synchronicity is very dependent on the TTL design of the flip-flop.

Differentiation between Setup/Hold and Recovery/Removal times is often necessary when verifying the timing of larger circuits because asynchronous signals may be found to be less critical than synchronous signals. The differentiation offers circuit designers the ability to define the verification conditions for these types of signals independently.

The metastability in flip-flops can be avoided by ensuring that the data and control inputs are held valid and constant for specified periods before and after the clock pulse, called the setup time (t_su) and the hold time (t_h) respectively. These times are specified in the data sheet for the device, and are typically between a few nanoseconds and a few hundred picoseconds for modern devices.

Unfortunately, it is not always possible to meet the setup and hold criteria, because the flip-flop may be connected to a real-time signal that could change at any time, outside the control of the designer. In this case, the best the designer can do is to reduce the probability of error to a certain level, depending on the required reliability of the circuit. One technique for suppressing metastability is to connect two or more flip-flops in a chain, so that the output of each one feeds the data input of the next, and all devices share a common clock. With this method, the probability of a metastable event can be reduced to a negligible value, but never to zero. The probability of metastability gets closer and closer to zero as the number of flip-flops connected in series is increased.

So-called metastable-hardened flip-flops are available, which work by reducing the setup and hold times as much as possible, but even these cannot eliminate the problem entirely. This is because metastability is more than simply a matter of circuit design. When the transitions in the clock and the data are close together in time, the flip-flop is forced to decide which event happened first. However fast we make the device, there is always the possibility that the input events will be so close together that it cannot detect which one happened first. It is therefore logically impossible to build a perfectly metastable-proof flip-flop.

Propagation delay

Another important timing value for a flip-flop is the clock-to-output delay (common symbol in data sheets: t_CO) or propagation delay (t_P), which is the time a flip-flop takes to change its output after the clock edge. The time for a high-to-low transition (t_PHL) is sometimes different from the time for a low-to-high transition (t_PLH).
When cascading flip-flops which share the same clock (as in a shift register), it is important to ensure that the t_CO of a preceding flip-flop is longer than the hold time (t_h) of the following flip-flop, so data present at the input of the succeeding flip-flop is properly "shifted in" following the active edge of the clock. This relationship between t_CO and t_h is normally guaranteed if the flip-flops are physically identical. Furthermore, for correct operation, it is easy to verify that the clock period has to be greater than the sum t_su + t_h.

Generalizations

Flip-flops can be generalized in at least two ways: by making them 1-of-N instead of 1-of-2, and by adapting them to logic with more than two states. In the special cases of 1-of-3 encoding, or multi-valued ternary logic, these elements may be referred to as flip-flap-flops.

In a conventional flip-flop, exactly one of the two complementary outputs is high. This can be generalized to a memory element with N outputs, exactly one of which is high (alternatively, where exactly one of N is low). The output is therefore always a one-hot (respectively one-cold) representation. The construction is similar to a conventional cross-coupled flip-flop; each output, when high, inhibits all the other outputs. Alternatively, more or less conventional flip-flops can be used, one per output, with additional circuitry to make sure only one at a time can be true.

Another generalization of the conventional flip-flop is a memory element for multi-valued logic. In this case the memory element retains exactly one of the logic states until the control inputs induce a change. In addition, a multiple-valued clock can also be used, leading to new possible clock transitions.

RAM (Random-access memory)

2013-12-23T21:21:00.001+05:30

Random-access memory

Random-access memory (RAM /ræm/) is a form of computer data storage. A random-access device allows stored data to be accessed directly in any random order. In contrast, other data storage media such as hard disks, CDs, DVDs and magnetic tape, as well as early primary memory types such as drum memory, read and write data only in a predetermined order, consecutively, because of mechanical design limitations.

Therefore, the time to access a given data location varies significantly depending on its physical location.
Today, random-access memory takes the form of integrated circuits. Strictly speaking, modern types of DRAM are not random access, as data is read in bursts, although the name DRAM / RAM has stuck.

However, many types of SRAM, ROM, OTP, and NOR flash are still random access even in a strict sense. RAM is normally associated with volatile types of memory (such as DRAM memory modules), where its stored information is lost if the power is removed. Many other types of non-volatile memory are RAM as well, including most types of ROM and a type of flash memory called NOR-Flash. The first RAM modules to come into the market were created in 1951 and were sold until the late 1960s and early 1970s.

History

Early computers used relays, or delay lines for "main" memory functions. Ultrasonic delay lines could only reproduce data in the order it was written. Drum memory could be expanded at low cost but retrieval of non-sequential memory items required knowledge of the physical layout of the drum to optimize speed. Latches built out of vacuum tube triodes, and later, out of discrete transistors, were used for smaller and faster memories such as random-access register banks and registers. Such registers were relatively large, power-hungry and too costly to use for large amounts of data; generally only a few hundred or few thousand bits of such memory could be provided.

Magnetic core memory was the standard form of memory system until displaced by solid-state memory in integrated circuits, starting in the early 1970s. Robert H. Dennard invented dynamic random-access memory (DRAM) in 1968; this allowed replacement of a 4 or 6-transistor latch circuit by a single transistor for each memory bit, greatly increasing memory density at the cost of volatility. Data was stored in the tiny capacitance of each transistor, and had to be periodically refreshed in a few milliseconds before the charge could leak away.
Prior to the development of integrated read-only memory (ROM) circuits, permanent (or read-only) random-access memory was often constructed using diode matrices driven by address decoders, or specially wound core rope memory planes.

Types of RAM

The three main forms of modern RAM are static RAM (SRAM), dynamic RAM (DRAM) and phase-change memory (PRAM). In SRAM, a bit of data is stored using the state of a flip-flop. This form of RAM is more expensive to produce, but is generally faster and requires less power than DRAM and, in modern computers, is often used as cache memory for the CPU. DRAM stores a bit of data using a transistor and capacitor pair, which together comprise a memory cell. The capacitor holds a high or low charge (1 or 0, respectively), and the transistor acts as a switch that lets the control circuitry on the chip read the capacitor's state of charge or change it. As this form of memory is less expensive to produce than static RAM, it is the predominant form of computer memory used in modern computers.

Both static and dynamic RAM are considered volatile, as their state is lost or reset when power is removed from the system. By contrast, read-only memory (ROM) stores data by permanently enabling or disabling selected transistors, such that the memory cannot be altered. Writeable variants of ROM (such as EEPROM and flash memory) share properties of both ROM and RAM, enabling data to persist without power and to be updated without requiring special equipment. These persistent forms of semiconductor ROM include USB flash drives, memory cards for cameras and portable devices, etc. ECC memory (which can be either SRAM or DRAM) includes special circuitry to detect and/or correct random faults (memory errors) in the stored data, using parity bits or error correction code.

In general, the term RAM refers solely to solid-state memory devices (either DRAM or SRAM), and more specifically the main memory in most computers. In optical storage, the term DVD-RAM is somewhat of a misnomer since, unlike CD-RW or DVD-RW it does not need to be erased before reuse. Nevertheless a DVD-RAM behaves much like a hard disc drive if somewhat slower.

Memory hierarchy

Main article: Memory hierarchy

One can read and over-write data in RAM. Many computer systems have a memory hierarchy consisting of CPU registers, on-die SRAM caches, external caches, DRAM, paging systems and virtual memory or swap space on a hard drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the random access term in RAM. Even within a hierarchy level such as DRAM, the specific row, column, bank, rank, channel, or interleave organization of the components make the access time variable, although not to the extent that rotating storage media or a tape is variable. The overall goal of using a memory hierarchy is to obtain the higher possible average access performance while minimizing the total cost of the entire memory system (generally, the memory hierarchy follows the access time with the fast CPU registers at the top and the slow hard drive at the bottom).

In many modern personal computers, the RAM comes in an easily upgraded form of modules called memory modules or DRAM modules about the size of a few sticks of chewing gum. These can quickly be replaced should they become damaged or when changing needs demand more storage capacity. As suggested above, smaller amounts of RAM (mostly SRAM) are also integrated in the CPU and other ICs on the motherboard, as well as in hard-drives, CD-ROMs, and several other parts of the computer system.

Other uses of RAM

In addition to serving as temporary storage and working space for the operating system and applications, RAM is used in numerous other ways.

Virtual memory

Main article: virtual memory

Most modern operating systems employ a method of extending RAM capacity, known as "virtual memory". A portion of the computer's hard drive is set aside for a paging file or a scratch partition, and the combination of physical RAM and the paging file form the system's total memory. (For example, if a computer has 2 GB of RAM and a 1 GB page file, the operating system has 3 GB total memory available to it.) When the system runs low on physical memory, it can "swap" portions of RAM to the paging file to make room for new data, as well as to read previously swapped information back into RAM. Excessive use of this mechanism results in thrashing and generally hampers overall system performance, mainly because hard drives are far slower than RAM.

RAM disk

Software can "partition" a portion of a computer's RAM, allowing it to act as a much faster hard drive that is called a RAM disk. A RAM disk loses the stored data when the computer is shut down, unless memory is arranged to have a standby battery source.

Shadow RAM

Sometimes, the contents of a relatively slow ROM chip are copied to read/write memory to allow for shorter access times. The ROM chip is then disabled while the initialized memory locations are switched in on the same block of addresses (often write-protected). This process, sometimes called shadowing, is fairly common in both computers and embedded systems.

As a common example, the BIOS in typical personal computers often has an option called “use shadow BIOS” or similar. When enabled, functions relying on data from the BIOS’s ROM will instead use DRAM locations (most can also toggle shadowing of video card ROM or other ROM sections). Depending on the system, this may not result in increased performance, and may cause incompatibilities. For example, some hardware may be inaccessible to the operating system if shadow RAM is used. On some systems the benefit may be hypothetical because the BIOS is not used after booting in favor of direct hardware access. Free memory is reduced by the size of the shadowed ROMs.

Recent developments

Several new types of non-volatile RAM, which will preserve data while powered down, are under development. The technologies used include carbon nanotubes and approaches utilizing the magnetic tunnel effect. Amongst the 1st generation MRAM, a 128 KiB (128 × 2¹⁰ bytes) magnetic RAM (MRAM) chip was manufactured with 0.18 µm technology in the summer of 2003. In June 2004, Infineon Technologies unveiled a 16 MiB (16 × 2²⁰ bytes) prototype again based on 0.18 µm technology. There are two 2nd generation techniques currently in development: Thermal Assisted Switching (TAS) which is being developed by Crocus Technology, and Spin Torque Transfer (STT) on which Crocus, Hynix, IBM, and several other companies are working. Nantero built a functioning carbon nanotube memory prototype 10 GiB (10 × 2³⁰ bytes) array in 2004. Whether some of these technologies will be able to eventually take a significant market share from either DRAM, SRAM, or flash-memory technology, however, remains to be seen.

Since 2006, "solid-state drives" (based on flash memory) with capacities exceeding 256 gigabytes and performance far exceeding traditional disks have become available. This development has started to blur the definition between traditional random-access memory and "disks", dramatically reducing the difference in performance.

Some kinds of random-access memory, such as "EcoRAM", are specifically designed for server farms, where low power consumption is more important than speed.

Memory wall

The "memory wall" is the growing disparity of speed between CPU and memory outside the CPU chip. An important reason for this disparity is the limited communication bandwidth beyond chip boundaries. From 1986 to 2000, CPU speed improved at an annual rate of 55% while memory speed only improved at 10%. Given these trends, it was expected that memory latency would become an overwhelming bottleneck in computer performance.
CPU speed improvements slowed significantly partly due to major physical barriers and partly because current CPU designs have already hit the memory wall in some sense. Intel summarized these causes in a 2005 document.

“First of all, as chip geometries shrink and clock frequencies rise, the transistor leakage current increases, leading to excess power consumption and heat... Secondly, the advantages of higher clock speeds are in part negated by memory latency, since memory access times have not been able to keep pace with increasing clock frequencies. Third, for certain applications, traditional serial architectures are becoming less efficient as processors get faster (due to the so-called Von Neumann bottleneck), further undercutting any gains that frequency increases might otherwise buy. In addition, partly due to limitations in the means of producing inductance within solid state devices, resistance-capacitance (RC) delays in signal transmission are growing as feature sizes shrink, imposing an additional bottleneck that frequency increases don't address.”

The RC delays in signal transmission were also noted in Clock Rate versus IPC: The End of the Road for Conventional Microarchitectures which projects a maximum of 12.5% average annual CPU performance improvement between 2000 and 2014. The data on Intel Processors clearly shows a slowdown in performance improvements in recent processors. However, Intel's Core 2 Duo processors (codenamed Conroe) showed a significant improvement over previous Pentium 4 processors; due to a more efficient architecture, performance increased while clock rate actually decreased.

Make your own PCB at Home

2013-12-01T13:24:00.000+05:30

Make your own PCB at Home

Printed circuit board or PCB is one of the important things to assemble an electronic circuit. The pins/leads are then soldered to connect with the PCB tracks. Here it explains the easiest method to make a PCB at home for prototyping. To make the PCB,

following materials are required

1. Copper clad board

The copper clad is available in standard sizes. Cut it to the required size using a Hacksaw blade. The copper clad board has a copper coated side which forms the soldering side. The other side is the component side on which the components are placed.

2. Ferric chloride solution

This is the Etching solution of Ferric chloride. It removes the unwanted copper layers from

3. PCB drill and bits

PCB drill is used to drill holes in the PCB. A hand drill with suitable bits is sufficient for the purpose. Use drill bits of the following size to make holes for different components

4. Tonner remover

Usually paint thinner is used for removing the tonner.

5. Cleaning solution

The copper clad may be deposited with oil and other impurities, we can use dish wash liquids like prill to clean the board

PCB Making

PCB making involves the following stages

1. Select the layout that we have to print on the board. Print it on a 130 GSM photo paper using laser printer with the maximum darkness possible.

2. Cut the copper clad to required size and clean the board using dish wash liquids like Pril and scrub using scrubber like scrotchbyte to remove the impurity and oil.

Fig 2:

3. Place the print out on top of the board. Be care full with the alignment, as the print out paper will stick to the board soon.

4. Pre heat the board using a hot iron box and Iron the print out for 5-6 minutes.

5. Once, when the print gets stick to the board, immerse the whole board in warm water. The paper will start to soak, then peel the paper using your thump finger. Remove the paper to the finest level.

6. Once the whole paper is removed, the board is ready for etching.

7. Take a Plastic or Porcelain tray and place the copper clad board with the track side facing upwards. Carefully pour the Ferric chloride solution over the copper clad till the copper clad is immersed in the ferric chloride. Shake the container for faster etching. Heating the solution before the process will give you a better result.

8. After etching, clean the copper clad using tap water. This will remove the dissolved copper from the copper laminate except the copper beneath Tonner.

9. Drill holes using appropriate drill bits.

10. Remove the Tonner using paint thinner and cotton waste so that the tracks will appear as copper lines.

11. If required, tin the tracks carefully using solder lead. Dip in varnish to prevent copper oxidation in tracks.

Caution: Ferric chloride solution is toxic. It can cause skin burning or irritation. Use hand gloves during etching. Do not spill the ferric chloride on the skin. If this happens accidently, wash with water. Do not keep ferric chloride in places access to children.

Things To Do Before Applying For Adsense

2013-11-09T16:33:00.000+05:30

Things To Do Before Applying For Adsense

In this post, I am turning my head towards a new thing. That is "Adsense".

What Is Adsense ?

Google AdSense is a program run by Google Inc. that allows publishers in the Google Network of content sites to serve automatic text, image, video, and rich media adverts that are targeted to site content and audience. These adverts are administered, sorted, and maintained by Google, and they can generate revenue on either a per-click or per-impression basis. Google beta-tested a cost-per-action service, but discontinued it in October 2008 in favor of a DoubleClick offering (also owned by Google). In Q1 2011, Google earned US$2.43 billion ($9.71 billion annualized), or 28% of total revenue, through Google AdSense.

source : www.wikipedia.org

Google Adsense is an ad providing program from Google. You can get dollars per impressions and click on ads. But getting adsense approval is not so easy in the present days. So your website needs to well designed for adsense approval.

Today, I am describing how to arrange your blog for getting adsense approved. For this you have to do many things. I will describe about 15 of that. Just please do these and wait for my next post. The main points to keep in mind are :

Add Meta Tags
Length Of Posts
Site Traffic
Google Widgets
Pages
Domain
Invalid Content
Webmaster Quality Guidelines
DMCA Badge [ optional ]
Chat-boxes
Copy Content
Posts
Age Of Domain

Adding Meta Tags

You have to add the meta tags for better traffic. But you have to add only the necessary ones into your template. If you had added any meta tags or if you haven't added [ add below <head> of your template], check with this code :

<meta content='YOUR BLOG TITLE' name='title'/>
<b:if cond='data:blog.metaDescription != ""'>
<meta expr:content='data:blog.metaDescription' name='description'/>
</b:if>
<b:if cond='data:blog.url == data:blog.homepageUrl'> <meta content='YOUR BLOG DESCRIPTION' name='description'/></b:if>
<meta content='KEYWORDS HERE' name='keywords'/>
<meta content='AUTHOR NAME' name='author'/>
<meta content='INDEX,FOLLOW' name='robots'/>
<meta content='index, follow' name='googlebot'/>
<meta content='text/html; charset=UTF-8' http-equiv='content-type'/>

Replace this with your Blog Title : YOUR BLOG TITLE
Replace this with your blog description : YOUR BLOG DESCRIPTION
Replace this with keywords [ each one separated by a comma and not too much ] : KEYWORDS HERE
Replace this with the author name : AUTHOR NAME

Other bold texts need not be changed.

Length Of Posts

Every posts must exceed a length of approximately 750 words or more ]. If your posts are not exceeding this limit, Google will say that your posts are of short lengths.
And also, check for major grammar mistakes.

Site Traffic

When you are going to submit your site to adsense, your site traffic might exceed a limit of 300. [ When my adsense account got approved, it was above 5000].

The site traffic can be divided into two :

Organic Traffic.
Inorganic traffic.

Organic Traffic

Organic traffic means the traffic that you get from search engines and that comes directly to your site.

Inorganic traffic

Inorganic traffic means the traffic that you get from social media like [ Google plus, Facebook, Twitter etc.]

Google Widgets

Its better to use the google widgets on your blog. That includes add to circles widget and the +1 button.

Domain

You have to change your web address www.yoursite.blogspot.com into www.yoursite.com.

You can choose any of these for blog into a paid domain :

www.bigrock.com
www.hostgator.com
www.godaddy.com

Invalid Content

Check every post for any invalid content.

Google Webmaster Tools

First of all, you have to submit your website to Google webmaster tools.

Submit Sitemap :

You just submit the sitemap to your Google webmaster tools and to make sure that every pages had been indexed by Google. If you have any doubts in submitting sitemap, please use the comment box.

Meet With Webmaster Quality Guidelines

You have to read this article from Google and make your website agrees with these quality guidelines :

http://support.google.com/webmasters/bin/answer.py?hl=en&answer=35769

Some include adding alt tags and robots.txt files.

DMCA Badge [ OPTIONAL]

You have to protect your content from being copied. So you have to add the DMCA badge to your site.

visit the site; http://www.dmca.com

Chat Boxes

Don't add any chat boxes on your blogger. Because according to Google, it is a form of policy violation. The reason behind is that you can force users to click on ads while chatting.

Copy Content

You should not post any copy content on your blogger or website. In case you have a copy content, provide the source of the content.

Posts

You should have at least 100 posts or articles on your blogger/website.

Age Of Domain

According to Google policies, your website must be 6 months old. In case if your are having massive traffic and totally unique posts on your blog, you will get adsense approved before 6 months.

Conclusion

After doing all these things, give me your website address here. I will say that is it ready for getting approved by adsense.

source;-netinfoz

If at all, you are having any doubt regarding this topic that I had mentioned :

You Must Use The Comment Box

File Systems - NTFS FAT FAT32 exFAT | Formatting USB Drives

2013-11-04T19:50:00.000+05:30

File Systems - NTFS FAT FAT32 exFAT | Formatting USB Drives

FILE SYSTEMS

In windows 7, there are four different file systems. They are :

· NTFS
· FAT
· FAT32
· exFAT

If your drive is larger than 32GB, FAT and FAT32 will not be available. Lets look at the benefits of each file systems.

NTFS as compared to FAT AND FAT32

· create partitions larger than 32GB

· compress files and save disk space.

· better space management = less fragmentation.

· allows more clusters on larger drives = less wasted space.

· add user permissions to individual files and folders (Windows Professional).

· on-the-fly file encryption using EFS (Encrypting File System; Windows Professional).

FAT AND FAT32 COMPARED TO NTFS

· Compatible with all operating systems.

· Takes up less space on USB drive.

· Faster and less memory usage.

exFAT COMPARED TO FAT AND FAT32

· Read/write files larger than 4 GB.

· Creates drive partitions larger than 32 GB.

· Better space management.

· Less fragmentation.

WHICH IS THE BEST?

Hard drives are organized in clusters and the allocation unit size describes the size of a single cluster. The file system records the state of each cluster, i.e. free or occupied. Hence, larger clusters can lead to more wasted or slack space. With smaller clusters, however, the drive becomes slower as each file is broken up into smaller pieces and it takes much longer to draw them all together when the file is accessed. Hence, larger clusters can lead to more wasted or slack space. With smaller clusters, however, the drive becomes slower as each file is broken up into smaller pieces and it takes much longer to draw them all together when the file is accessed. The thing you had to keep in mind is that :

Large drive / large files = large allocation size

If you are having a low size flashdrive, suppose 500MB, use FAT32 [ 512 bytes ] or FAT [ 32 KB ]. If you are having a large sized flashdrive, suppose 1 TB, use NTFS [ 64 KB ].

WHAT IS VOLUME LABEL?

Volume Label is just the name that we gives to our drive. You can give any name to your drive. But your volume label depends upon the filesystem that you are formatting with. That is given below:

NTFS

· Supports upto 32 characters.

· No tabs

· Uppercase and lowercase support, display as we enter.

FAT

· Supports upto 11 characters.

· No tabs

· Only uppercase.

· * ? . , ; : / \ | + = < > [ ], these characters are not supported.

source:netinfoz

Firefox's latest - and greatest - version!

2013-10-28T20:21:00.000+05:30

Firefox's latest - and greatest - version!

Mozilla Firefox is one of the World's most popular web browsers and was one of the first to break the stranglehold of Microsoft's Internet Explorer (IE) on the web browsing market.

Features

This is the latest version of the popular web browser and as always, Mozilla claim to a speedier, safer browsing experience. Tests reveal that this newest version of Mozilla Firefox is certainly quick to load even the most graphics intense pages.

Firefox also now features secure connections when performing Google searches to improve privacy and there's an updated site identity indicator in the URL bar. There's only one relevant improvement in the latest version of Firefox for most users relating to security. Security has been improved with mixed content blocking which protects users from "man-in-the-middle attacks" and from eavesdroppers on HTTPS pages. There are also several bug fixes.

Mozilla Firefox's tab layout is quite similar to Google's Chrome browser, instead of seeing a blank page whenever a new tab is opened Firefox users will now be treated to icons that offer quick access to everything from bookmarks to most recently accessed and most frequently visited sites.

These icons are fully customizable in Mozilla Firefox as well. You can click and drag them to any spot you like on your name tab's page. If you're not a fan, you can also go to the grid icon on the upper right side of your browser and erase them entirely.

Firefox features Facebook integration. Firefox supports Facebook's social API so you can have dedicated buttons for Facebook in your browser. Mozilla Firefox supports Facebook's Messenger within Firefox, giving users desktop notifications as well as a persistent friends list and activity feed on the right. Conversations will open up as overlays on top of whatever website you're on so you can multitask while you chat.

Spell Checking

A built-in spell checker works directly in Web pages, like blog posts and email. Save yourself a step and stop worrying about typos.

Download Manager

Download files seamlessly and securely! A pause and resume feature means you can stop and start anytime. So, if you’re halfway through downloading a big file and it’s time to catch the bus, just pause and pick up where you left off later. The resume function also works if your system crashes or is forced to restart. The manager shows your download progress and even lets you search your files by name or the Web address where the download came from.

Offline Browsing

Take your computer offline and still have your information at your fingertips. Certain sites may allow applications—like your Web-based email—to stay with you at all times.

Full Zoom

Want to see captions and pictures in a larger size? An elegant new zoom feature lets you swoop in and see the details on web pages, zeroing in on what matters. The pages will scale equally, with all the elements of layout changing at the same level.

Advanced Security

Dress Up Your Firefox with Themes

Change the look of your Firefox to practically anything with Themes: thousands of easy-to-install themes created by users from around the world (or that you make yourself!). With a single click, you can dress your browser up in simple designs, colorful patterns, and content from partners like Harry Potter and Bob Marley.

Anti-Malware

Firefox protects you from viruses, worms, trojan horses, and spyware delivered over the Web. If you accidentally access an attack site, it will warn you away from the site and tell you why it isn’t safe to use.

Instant Web Site ID

Want to be extra sure about a site’s legitimacy before you make a purchase? Click on its favicon for an instant identity overview. Another click digs deeper: how many times have you visited? Are your passwords saved? Check up on suspicious sites, avoid Web forgeries and make sure a site is what it claims to be.

Usability

Mozilla Firefox really changed the way people browse the web when it originally burst onto the scene. Today Firefox remains an incredibly powerful and customizable browser, although competition from Google Chrome has given it a definite run for its money.

Conclusion

In terms of interface, the latest version of Firefox isn't much different from previous versions, but the features it has added certainly make for a nicer, more enjoyable browsing experience overall.

Pros

Very secure

Quick to load

Lots of extensions to choose from

Fast, generally stable browser

Silent updates for Windows users

Cons

Memory leak persists for some

May not initially work with some add-ons

Recent changes

http://www.mozilla.org/en-US/firefox/24.0/releasenotes/

Download

Direct download

Pin No	Function	Name
1	Ground (0V)	Ground
2	Supply voltage; 5V (4.7V – 5.3V)	Vcc
3	Contrast adjustment; through a variable resistor	V_EE
4	Selects command register when low; and data register when high	Register Select
5	Low to write to the register; High to read from the register	Read/write
6	Sends data to data pins when a high to low pulse is given	Enable
7	8-bit data pins	DB0
8		DB1
9		DB2
10		DB3
11		DB4
12		DB5
13		DB6
14		DB7
15	Backlight V_CC (5V)	Led+
16	Backlight Ground (0V)	Led-

Techi yard

Microcontroller - Introduction

Microcontroller

AVR

16x2 LCD Module

16x2 LCD

Xiaomi Mi 3 full specification and Buy now

Xiaomi Mi 3

Accelerate your life

The fastest Mi phone ever

A dragon in your pocket

2GB LPDDR3 RAM

Stunningly beautiful

13MP camera with dual-LED flash

Power through your day

Lose the wires

Amazing from the inside out

Make Android yours

Technical Specifications

Weight and dimensions

Water Sensor Circuit

Water Sensor Circuit

Vehicle Indicator circuit

Vehicle Indicator circuit

Basic Computer Terms You Should Know Before Buying A PC

Basic Computer Terms You Should Know Before Buying a PC

The Processor

The RAM

Optical Drive

Wireless Network Card

Network Card

Operating System

Hard Drive

Video Card

Monitor

battery charger circuit & battery level indicator with low battery recharge alarm

battery charger circuit & battery level indicator with low battery recharge alarm

Circuit diagram of battery charger

Components required

Working of battery charger circuit

What fevikwik made of?

What fevikwik made of?

Cyanoacrylate

Development

Properties

Uses

Safety issues

Toxicity

Reaction with cotton

Solvents and debonders

Shelf life

How Intel makes integrated circuit chips?

How Intel makes integrated circuit chips

From sand to circuits

Revolutionary

Design

Moore’s Law

Fabrication

Silicon, the principalingredient in beachsand, is a naturalsemiconductor andthe most commonelement on earthafter oxygen.

Process

Performing More Fabrication Steps

Doping

Metallization

Completing the wafer

Testing and Packaging

High-performance packages

One more check

Innovation

Undisputed Leadership

Unwavering commitment to moving technology forward

Terminology

Remote Tester Circuit

Remote Tester Circuit

Cell Phone Controlled Home appliances

Cell Phone Controlled Home appliances

Relay

Relay

Basic design and operation

Types

Latching relay

Silicon, the principal
ingredient in beach
sand, is a natural
semiconductor and
the most common
element on earth
after oxygen.

Rated current I_N

The I²t value