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SYLLABUS

noreply@blogger.com (Unknown) — Fri, 15 Nov 2013 16:30:00 +0000

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Servo Motor

noreply@blogger.com (Unknown) — Fri, 30 Aug 2013 07:00:00 +0000

What are Servo Motors?

Servo refers to an error sensing feedback control which is used to correct the performance of a system. Servo or RC Servo Motors are DC motors equipped with a servo mechanism for precise control of angular position. The RC servo motors usually have a rotation limit from 90° to 180°. Some servos also have rotation limit of 360° or more. But servos do not rotate continually. Their rotation is restricted in between the fixed angles.

Where are Servos used?

The Servo motors are used for precision positioning. They are used in robotic arms and legs, sensor scanners and in RC toys like RC helicopter, airplanes and cars
ervo Motor manufacturers

There are four major manufacturers of servo motors: Futaba, Hitec, Airtronics and JR radios. Futaba and Hitec servos have nowadays dominated the market. Their servos are same except some interfacing differences like the wire colors, connector type, spline etc.

Servo Motor Manufacturers

Servo Motor wiring and plugs
The Servo Motors come with three wires or leads. Two of these wires are to provide ground and positive supply to the servo DC motor. The third wire is for the control signal. These wires of a servo motor are color coded. The red wire is the DC supply lead and must be connected to a DC voltage supply in the range of 4.8 V to 6V. The black wire is to provide ground. The color for the third wire (to provide control signal) varies for different manufacturers. It can be yellow (in case of Hitec), white (in case of Futaba), brown etc.

Futaba provides a J-type plug with an extra flange for proper connection of the servo. Hitec has an S-type connector. A Futaba connector can be used with a Hitec servo by clipping of the extra flange. Also a Hitec connector can be used with a Futaba servo just by filing off the extra width so that it fits in well.

Hitec splines have 24 teeth while Futaba splines are of 25 teeth. Therefore splines made for one servo type cannot be used with another. Spline is the place where a servo arm is connected. It is analogous to the shaft of a common DC motor.

Structure of Servo Motor

Unlike DC motors, reversing the ground and positive supply connections does not change the direction (of rotation) of a servo. This may, in fact, damage the servo motor. That is why it is important to properly account for the order of wires in a servo motor.

What is the difference between a DC motor and servo motor?

noreply@blogger.com (Unknown) — Fri, 30 Aug 2013 06:40:00 +0000

A DC motor has a two wire connection. All drive power is supplied over these two wires—think of a light bulb. When you turn on a DC motor, it just starts spinning round and round. Most DC motors are pretty fast, about 5000 RPM (revolutions per minute).

With the DC motor, its speed (or more accurately, its power level) is controlled using a technique named pulse width modulation, or simply PWM. This is idea of controlling the motor’s power level by strobing the power on and off. The key concept here is duty cycle—the percentage of “on time” versus“off time.” If the power is on only 1/2 of the time, the motor runs with 1/2 the power of its full-on operation.

If you switch the power on and off fast enough, then it just seems like the motor is running weaker—there’s no stuttering. This is what PWM means when referring to DC motors. The Handy Board’s DC motor power drive circuits simply switch on and off, and the motor runs more slowly because it’s only receiving power for 25%, 50%, or some other fractional percentage of the time.

A servo motor is an entirely different story. The servo motor is actually an assembly of four things: a normal DC motor, a gear reduction unit, a position-sensing device (usually a potentiometer—a volume control knob), and a control circuit.

The function of the servo is to receive a control signal that represents a desired output position of the servo shaft, and apply power to its DC motor until its shaft turns to that position. It uses the position-sensing device to determine the rotational position of the shaft, so it knows which way the motor must turn to move the shaft to the commanded position. The shaft typically does not rotate freely round and round like a DC motor, but rather can only turn 200 degrees or so back and forth.

The servo has a 3 wire connection: power, ground, and control. The power source must be constantly applied; the servo has its own drive electronics that draw current from the power lead to drive the motor.

The control signal is pulse width modulated (PWM), but here the duration of the positive-going pulse determines the position of the servo shaft. For instance, a 1.520 millisecond pulse is the center position for a Futaba S148 servo. A longer pulse makes the servo turn to a clockwise-from-center position, and a shorter pulse makes the servo turn to a counter-clockwise-from-center position.

The servo control pulse is repeated every 20 milliseconds. In essence, every 20 milliseconds you are telling the servo, “go here.”

To recap, there are two important differences between the control pulse of the servo motor versus the DC motor. First, on the servo motor, duty cycle (on-time vs. off-time) has no meaning whatsoever—all that matters is the absolute duration of the positive-going pulse, which corresponds to a commanded output position of the servo shaft. Second, the servo has its own power electronics, so very little power flows over the control signal. All power is draw from its power lead, which must be simply hooked up to a high-current source of 5 volts.

Contrast this to the DC motor. On the Handy Board, there are specific motor driver circuits for four DC motors. Remember, a DC motor is like a light bulb; it has no electronics of its own and it requires a large amount of drive current to be supplied to it. This is the function of the L293D chips on the Handy Board, to act as large current switches for operating DC motors.

Plans and software drivers are given to operate two servo motors from the HB. This is done simply by taking spare digital outputs, which are used to generate the precise timing waveform that the servo uses as a control input. Very little current flows over these servo control signals, because the servo has its own internal drive electronics for running its built-in motors.

Applications of Microcontroller

noreply@blogger.com (Unknown) — Wed, 26 Jun 2013 13:31:00 +0000

The reason I find microcontrollers fascinating is that they have been and continue to be such an important part of the electronics industry. Over the past decade and more microcontrollers have been creeping into our daily lives. Figure 1 shows how microcontrollers increased in popularity from 1991 through 1996.

In today’s world, microcontrollers are used in just about every electronic object in the household and place of business. Just about the only common object in the house that does not have a microcontroller in it is the light bulb. In fifteen years or so even that may not be the case.

The reason microcontrollers have become so common is that they are more than merely reliable. By adding a small computer to many devices it is possible to increase efficiency or safety, or any number of other features.

Timing devices are now composed almost entirely of microcontrollers. This has made them unbelievably accurate. They are also cheap, and much more reliable. A digital watch today, which has no moving parts, is almost impossible to break through normal use. It is easy to adapt digital watches to extreme environments such as the deep sea or vacuum.

Telephones and other personal communication devices also use microcontrollers. With such devices it is possible to have wireless telephones and cellular phones, each capable of maintaining a connection between the phone unit and some sort of base station. These phones can also encrypt data as it leaves and decrypt it as it comes in.

Televisions and stereos use microcontrollers. Neither is the mess of tubes that was synonymous with televisions and radios. As a result, both produce better quality picture and sound, have more features, and weigh less per unit volume.

All kinds of transportation systems use microcontrollers. Cars use them in fuel injection systems, brakes, airbags, and just about any other piece of equipment.

Airplanes are going to a “fly-by-wire” control system. This is a complex computer interface between the controls that the pilot uses and the control surfaces of the plane. Such interfaces are controlled by microcontrollers.

Modern traffic lights are controlled by microcontrollers. Emergency phones by the highways of America have solar panels, batteries, and a microcontroller circuit to operate in remote areas.

Microcontroller's use increased rapidly. Now these are used in almost every electronic equipment like Washing Machines, Mobile Phones and Microwave Oven. Following are the most important facts about Microcontrollers, which causes rapid growth of their use:

Microcontrollers are cheap and very small in size, therefore they can be embedded on any device.

Programming of Microcontrollers is simple to learn. Its not much complicated.

We can use simulators on Computers to see the practical results of our program. Thus we can work on a Embedded project without even buying the required Components and Chips. Thus we can virtually see the working of our project or program.

Microcontrollers are mostly used in following electronic equipments :

Mobile Phones
Auto Mobiles
CD/DVD Players
Washing Machines
Cameras
In Computers-> Modems and Keyboard Controllers
Security Alarms
Electronic Measurement Instruments.
Microwave Oven

ARCHITECTURE OF 8051

noreply@blogger.com (Unknown) — Sat, 22 Jun 2013 18:03:00 +0000

Each block will be discussed step by step:

ALU — Arithmetic Logical Unit
This unit is used for the arithmetic calculations.

A-Accumulator
This register is used for arithmetic operations. This is also bit addressable and 8 bit register.

B-Register
This register is used in only two instructions MUL AB and DIV AB. This is also bit addressable and 8 bit register.

PC-Program Counter
• Points to the address of next instruction to be executed from ROM
• It is 16 bit register means the 8051 can access program address from 0000H to FFFFH. A total of 64KB of code. 16 bit register means. Initial value 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 (0000H)
Final value 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 (F F F F H)
• Initially PC has 0000H
• ORG instruction is used to initialize the PC ORG 0000H means PC initialize by 0000H

• PC is incremented after each instruction.

Example:

Mnemonics Machine codes

MOV R5, #25H 7D 25

MOV A, #00H 74 00

ADD A, R5 2D

HERE: SJMP HERE; 80 FE

• When 7D is accessed then PC locate the 0001H (next instruction to be executed)

• When 00 is accessed then PC locate the 0004H (next instruction to be executed)

ROM Memory Map in 8051

→ 4KB, 8KB, 16KB, 32KB, 64KB on chip ROM is available.

→ Max ROM space is 64 KB because 16 bit address line is available in 8051.

→ Starting address for ROM is 0000H (because PC which points the ROM is 16 bit wide).

8051 Flag Bits and PSW Register

→ Used to indicate the Arithmetic condition of ACC.

→ Flag register in 8051 is called as program status word (PSW). This special function register PSW is also bit addressable and 8 bit wide means each bit can be set or reset independently.

There are four flags in 8051

• P → Parity flag → PSW 0.0

1 – odd number of 1 in ACC

0 – even number of 1 in ACC

• OV(PSW 0.2) → overflow flag → this is used to detect error in signed

arithmetic operation. This is similar to carry flag but difference is only that

carry flag is used for unsigned operation.

• RS1(PSW0.4) RS0(PSW0.3) Register Bank Select

0 0 Bank 0

0 1 Bank 1

1 0 Bank 2

1 1 Bank 3

for selecting Bank 1, we use following commands

SETB PSW0.3 (means RS0=1)

CLR PSW0.4 (means RS1=0)

Initially by default always Bank 0 is selected.

• F0 → user definable bit

• AC → Auxiliary carry flag → when carry is generated from D3 to D4, it

is set to 1, it is used in BCD arithmetic.

Since carry is generated from D3 to D4, so AC is set.

•CY → carry flag → Affected after 8 bit addition and subtraction. It is used to detect error in unsigned arithmetic opr. We can also use it as single bit storage.

SETB C → for cy = 1

CLR C → for cy = 0

Structure of RAM or 8051 Register Bank and Stack

→ 128 byte RAM is available in 8051

→ 128 byte = 2^7B

Address range of RAM is 00H to 7FH.

→ In MC8051, 128 byte visible or user accessible RAM is available which is shown in figure. Extra 128B RAM which is not user accessible. 80H to FFH used for storage of SFR (special function register)

→ Four Register Banks

→ There are four register banks, in each register bank there are eight 8 bit register available from R0 to R7

→ By default Bank 0 is selected. For Bank 0, R0 has address 00H

R1 has address 01H

. . . . . . . . . . . . . . . .

R7 has address 07H

For Bank 1, R0 has address 08H

R1 has address 09H

. . . . . . . . . . . . . . . .

R7 has address 0FH

For selecting banks we use RS0 and RS1 bit of PSW.

→ R0 to R7 registers are byte addressable means.

If we want to set the bit 3 of R0 then we can’t use SETB R0.3 We use MOV R0, #08H;

For changing single bit we can modify all the other bits of R0.

→ Locations 20H to 2FH is bit addressable RAM means each bit from 00H to FFH in this we can set or reset CF rather than changing whole byte.

→ Locations 30H to 7FH is used as scratch pad means we can use this space for data reading and writing or for data storage.

Stack in 8051

→ RAM locations from 08H to 1FH can be used as stack. Stack is used to store the data temporarily. Stack is last in first out (LIFO)

→ Stack pointer (SP) →

• 8bit register

• It indicate current RAM address available for stack or it points the top of stack.

• Initially by default at 07H because first location of stack is 08H.

• After each PUSH instruction the SP is incremented by one while in MC after PUSH instruction SP is decremented.

• After each POP instruction the SP is decremented.

Example:

MOV R6,#25H;

MOV R1,#12H;

MOV R4,#OF3H;

PUSH 06H;

PUSH 01H;

POP 04H;

→ if we want to use more than 24byte (08H to 1FH) of stack. We can change SP to point RAM address 30H to 7FH by MOV SP, #XX Any value from 30 to 7FH

Conflicting of Register Banks and Stack

→ We know locations from 08H to 1FH is used as stack and it is also used as register bank.

→ If in the program, we use the Register Bank 1 to 3 and also use the stack then conflicts exist and error can be possible. For removing this situation we use the stack from location 30H to 7FH by shifting SP to 2FH. MOV SP,#2FH;

DPTR

→ Data Pointer in 8051

→ 16 bit register, it is divided into two parts DPH and DPL.

→ DPH for Higher order 8 bits, DPL for lower order 8 bits.

→ DPTR, DPH, DPL these all are SFRs in 8051.

Special Function Register

→ (See Fig.) RAM scratch pad, there is extra 128 byte RAM which is used to store the SFRs

→ Following figure shows special function bit address, all access to the four I/O ports CPU register, interrupt control register, timer/counter, UART, power control are performed through registers between 80H and FFH.

Byte Addressable SFR with byte address

SP – Stack printer – 81H

DPTR – Data pointer 2 bytes

DPL – Low byte – 82H

DPH – High byte – 83H

TMOD – Timer mode control – 89H

TH0 – Timer 0 Higher order bytes – 8CH

TL0 – Timer 0 Low order bytes – 8AH

TH1 – Timer 1 High bytes = 80H

TL1 – Timer 1 Low order byte = 86H

SBUF – Serial data buffer = 99H

PCON – Power control – 87H.

PIN DIAGRAM OF 8051

noreply@blogger.com (Unknown) — Wed, 19 Jun 2013 16:28:00 +0000

Description of each pin is discussed here:
•VCC → 5V supply
• VSS → GND
• XTAL2/XTALI are for oscillator input
• Port 0 – 32 to 39 – AD0/AD7 and P0.0 to P0.7
• Port 1 – 1 to 8 – P1.0 to P1.7
• Port 2 – 21 to 28 – P2.0 to P2.7 and A 8 to A15
• Port 3 – 10 to 17 – P3.0 to P3.7
• P 3.0 – RXD – Serial data input – SBUF
• P 3.1 – TXD – Serial data output – SBUF
• P 3.2 –INT0– External interrupt 0 – TCON 0.1
• P 3.3 –INT1– External interrupt 1 – TCON 0.3
• P 3.4 – T0 – External timer 0 input – TMOD
• P 3.5 – T1 – External timer 1 input – TMOD
• P 3.6 –WR– External memory write cycle – Active LOW
• P 3.7 –RD– External memory read cycle – Active LOW
• RST – for Restarting 8051
• ALE – Address latch enable
1 – Address on AD 0 to AD 7
0 – Data on AD 0 to AD 7
• PSEN – Program store enable

MICROCONTROLLER 8051 ARCHITECTURE

noreply@blogger.com (Unknown) — Wed, 19 Jun 2013 05:33:00 +0000

It is 8-bit microcontroller, means MC 8051 can Read, Write and Process 8 bit data. This is mostly used microcontroller in the robotics, home appliances like mp3 player, washing machines, electronic iron and industries. Mostly used blocks in the architecture of 8051 are as follows:

128 Byte RAM for Data Storage

MC 8051 has 128 byte Random Access memory for data storage. Random access memory is non volatile memory. During execution for storing the data the RAM is used. RAM consists of the register banks, stack for temporary data storage. It also consists of some special function register (SFR) which are used for some specific purpose like timer, input output ports etc. Normally microcontroller has 256 byte RAM in which 128 byte is used for user space which is normally Register banks and stack. But other 128 byte RAM which consists of SFRs. We will discuss the RAM in detail in next section.

Now what is the meaning of 128 byte RAM. What are address range which is provided for data storage. We will discuss here.

We know that 128 byte = 2^7 byte

Since 2^7 bytes so last 7 bits can be changed so total locations are from 00H to 7F H. This procedure of calculating the memory address is called as “memory mapping”. We can save data on memory locations from 00H to 7FH. Means total 128 byte space from 00H to 7FH is provided for data storage.

4KB ROM

• In 8051, 4KB read only memory (ROM) is available for program storage. This is used for permanent data storage. Or the data which is not changed during the processing like the program or algorithm for specific applications.

• This is volatile memory; the data saved in this memory does not disappear after power failure.

• We can interface up to 64KB ROM memory externally if the application is large. These sizes are specified different by their companies.

• Address Range of PC: Address range of PC means program counter (which points the next instruction to be executing) can be moved between these locations or we can save the program from this location to this location.

The address range can be calculated in the same way just like the RAM which is discussed in previous section.

Address range of PC is 0000H to 0FFFH means total 4KB locations are available from 0000H to 0FFFH. At which we can save the program.

Difference between RAM and ROM

• RAM is used for data storage while ROM is used for program storage.

• Data of RAM can be changed during processing while data of ROM can’t be changed during processing.

• We can take an example of calculator. If we want to perform addition of two numbers then we type the two numbers in calculator, this is saved in the RAM, but the Algorithms by which the calculation is performed is saved in the ROM. Data which is given by us to calculator can be changed but the algorithm or program by which calculation is performed can’t be changed.

Timers and Counters

Timer means which can give the delay of particular time between some events. For example on or off the lights after every 2 sec. This delay can be provided through some assembly program but in microcontroller two hardware pins are available for delay generation. These hardware pins can be also used for counting some external events. How much times a number is repeated in the given table is calculated by the counter.

• In MC8051, two timer pins are available T0 and T1, by these timers we can give the delay of particular time if we use these in timer mode.

• We can count external pulses at these pins if we use these pins in counter mode.

• 16 bits timers are available. Means we can generate delay between 0000H to FFFFH.

• Two special function registers are available.

• If we want to load T0 with 16 bit data then we can load separate lower 8 bit in TL0 and higher 8 bit in TH0.

• In the same way for T1.

• TMOD, TCON registers are used for controlling timer operation.

1.4.4 Serial Port

• There are two pins available for serial communication TXD and RXD.

• Normally TXD is used for transmitting serial data which is in SBUF register, RXD is used for receiving the serial data.

• SCON register is used for controlling the operation.

• There are four modes of serial communication which has been discussed in next chapter.

Input Output Ports

• There are four input output ports available P0, P1, P2, P3.

• Each port is 8 bit wide and has special function register P0, P1, P2, P3 which are bit addressable means each bit can be set or reset by the Bit instructions (SETB for high, CLR for low) independently.

• The data at any port which is transmitting or receiving is in these registers.

• The port 0 can perform dual works. It is also used as Lower order address bus (A0 to A7) multiplexed with 8 bit data bus P0.0 to P0.7 is AD0 to AD7 respectively the address bus and data bus is demultiplex by the ALE signal and latch which is further discussed in details.

• Port 2 can be used as I/O port as well as higher order address bus A8 to A15.

• Port 3 also have dual functions it can be worked as I/O as well as each pin of P3 has specific function.

P3.0 – RXD – Serial I / P for Asynchronous communication

Serial O / P for synchronous communication.

P3.1 – TXD – Serial data transmit.

P3.2 – INT0 – External Interrupt 0.

P3.3 – INT1 – External Interrupt 1.

P3.4 – T0 – Clock input for counter 0.

P3.5 – T1 – Clock input for counter 1.

P3.6 – WR – Signal for writing to external memory.

P3.7 – RD – Signal for reading from external memory.

When external memory is interfaced with 8051 then P0 and P2 can’t be worked as I/O port they works as address bus and data bus, otherwise they can be accessed as I/O ports.

Oscillator

• It is used for providing the clock to MC8051 which decides the speed or baud rate of MC.

• We use crystal which frequency vary from 4MHz to 30 MHz, normally we use 11.0592 MHz frequency.

Interrupts

• Interrupts are defined as requests because they can be refused (masked) if they are not used, that is when an interrupt is acknowledged. A special set of events or routines are followed to handle the interrupts. These special routines are known as interrupt handler or interrupt service routines (ISR). These are located at a special location in memory.

• INT0 and INT1 are the pins for external interrupts.

Introduction to Microcontroller

noreply@blogger.com (Unknown) — Tue, 18 Jun 2013 19:19:00 +0000

INTRODUCTION

The microcontroller incorporates all the features that are found in microprocessor. The microcontroller has built in ROM, RAM, Input Output ports, Serial Port, timers, interrupts and clock circuit. A microcontroller is an entire computer manufactured on a single chip. Microcontrollers are usually dedicated devices embedded within an application. For example, microcontrollers are used as engine controllers in automobiles and as exposure and focus controllers in cameras. In order to serve these applications, they have a high concentration of on-chip facilities such as serial ports, parallel input output ports, timers, counters, interrupt control, analog-to-digital converters, random access memory, read only memory, etc. The I/O, memory, and on-chip peripherals of a microcontroller are selected depending on the specifics of the target application. Since microcontrollers are powerful digital processors, the degree of control and programmability they provide significantly enhances the effectiveness of the application. The 8051 is the first microcontroller of the MCS-51 family introduced by Intel Corporation at the end of the 1970s. The 8051 family with its many enhanced members enjoys the largest market share, estimated to be about 40%, among the various microcontroller architectures.

The microcontroller has on chip peripheral devices. In this unit firstly we differentiate microcontroller from microprocessor then we will discuss about Hardware details of 8051 and then introduce the Assembly level language in brief.

MICROCONTROLLERS

• Microcontroller (MC) may be called computer on chip since it has basic features of microprocessor with internal ROM, RAM, Parallel and serial ports within single chip. Or we can say microprocessor with memory and ports is called as microcontroller. This is widely used in washing machines, vcd player, microwave oven, robotics or in industries.

• Microcontroller can be classified on the basis of their bits processed like

8bit MC, 16bit MC.

• 8 bit microcontroller, means it can read, write and process 8 bit data.

Ex. 8051 microcontroller. Basically 8 bit specifies the size of data bus. 8 bit microcontroller means 8 bit data can travel on the data bus or we can read, write process 8 bit data.

DIFFERENCE BETWEEN MICROCONTROLLER

AND MICROPROCESSOR

It is very clear from figure that in microprocessor we have to interface additional circuitry for providing the function of memory and ports, for example we have to interface external RAM for data storage, ROM for program storage, programmable peripheral interface (PPI) 8255 for the Input Output ports, 8253 for timers, USART for serial port. While in the microcontroller RAM, ROM, I/O ports, timers and serial communication ports are in built. Because of this it is called as “system on chip”. So in micro-controller there is no necessity of additional circuitry which is interfaced in the microprocessor because memory and input output ports are inbuilt in the microcontroller. Microcontroller gives the satisfactory performance for small applications. But for large applications the memory requirement is limited because only 64 KB memory is available for program storage. So for large applications we prefer microprocessor than microcontroller due to its high processing speed.

CRITERIA FOR SELECTION OF A MICROCONTROLLER

IN EMBEDDED SYSTEM

Criteria for selection of micro controller in any embedded system is as following:

(a) Meeting the computing needs of task at hand efficiently and cost effectively

• Speed of operation

• Packing

• Power consumption

• Amount of RAM and ROM on chip

• No. of I/O pins and timers on chip

• Cost

(b) Availability of software development tools such as compiler, assembler and debugger.

P-N Junction Diode

noreply@blogger.com (Unknown) — Tue, 18 Jun 2013 15:11:00 +0000

A p–n junction is a boundary or interface between two types of semiconductor material, p-type and n-type, inside a single crystal of semiconductor. It is created by doping, for example by ion implantation, diffusion of dopants, or by epitaxy (growing a layer of crystal doped with one type of dopant on top of a layer of crystal doped with another type of dopant). If two separate pieces of material were used, this would introduce a grain boundary between the semiconductors that severely inhibits its utility by scattering the electrons and holes.

When a P-type semiconductor is joined to a N-type semiconductor such that the crystal structure remains continuous at the boundary, a PN junction is formed. A PN junction forms a very useful device and can be called a semiconductor diode, PN junction diode, or simply a crystal diode. Simply joining two pieces together cannot form a PN junction, because it would produce a discontinuous crystal structure. Special techniques are required to assemble a PN junction. Normally P-type carriers are to the left of the junction and N-type carriers to the right.

Since the junction diode is a two terminal device, the application of voltage across its terminals leaves three possibilities:

No bias
Forward bias
Reverse bias

No bias

This occurs when there is no external voltage applied. The holes from the P-region diffuse into the N-region. They then combine with the free electrons in the N-region. The free electrons from the N-region diffuse into the P-region. These electrons combine with the holes.

Forward bias

When a battery is connected to the PN junction diode such that the positive terminal is connected to the P-side and negative terminal to the N-side, forward bias is created. When the PN junction is forward biased, the holes are repelled from the positive terminal and are forced to move towards the junction. Similarly, the electrons are repelled from the negative terminal of the battery and drift towards the junction. The current within the PN junction is the sum of electron current and hole current.

Reverse bias

A voltage source is connected with the positive terminal attached to the N-region and negative to the P-region. The holes in the P-region are attracted towards the negative terminal of the applied voltage, and the electrons in the N-region are attracted to the positive terminal. Thus the majority carriers are drawn away from the junction. This increases the barrier potential, which makes it more difficult for the carriers to diffuse across the junction.

P-N Junction Diode characteristics

The PN junction region of a Junction Diode has the following important characteristics:

1). Semiconductors contain two types of mobile charge carriers, Holes and Electrons.

2). The holes are positively charged while the electrons negatively charged.

3). A semiconductor may be doped with donor impurities such as Antimony (N-type doping), so that it contains mobile charges which are primarily electrons.

4). A semiconductor may be doped with acceptor impurities such as Boron (P-type doping), so that it contains mobile charges which are mainly holes.

5). The junction region itself has no charge carriers and is known as the depletion region.

6). The junction (depletion) region has a physical thickness that varies with the applied voltage.

7).When a diode is Zero Biased no external energy source is applied and a natural Potential Barrier is developed across a depletion layer which is approximately 0.5 to 0.7v for silicon diodes and approximately 0.3 of a volt for germanium diodes.

8). When a junction diode is Forward Biased the thickness of the depletion region reduces and the diode acts like a short circuit allowing full current to flow.

9). When a junction diode is Reverse Biased the thickness of the depletion region increases and the diode acts like an open circuit blocking any current flow, (only a very small leakage current).

E-book Digital Electronics

noreply@blogger.com (Unknown) — Tue, 18 Jun 2013 07:35:00 +0000

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Semiconductor

noreply@blogger.com (Unknown) — Fri, 14 Jun 2013 06:12:00 +0000

The magic word semiconductor is composed of two words-Semi and Conductor. Semi means not completely while conductor mean something, which can conduct electricity. Everybody is familiar with "Electricity". It is present everywhere; it runs many appliances in your home and outside the home like TV, Bulb, Freeze, and Microwave Oven etc. In simple terms, the current must past through wires so that the electricity can reach all these appliances. So a conductor is nothing but a material having ability to conduct this electricity. Semiconductors conduct electricity to some extent, less than the conductors, how much do you think? Well, it depends on the type of material or it's mixture and size. A semiconductor is a material that has intermediate conductivity between a conductor and an insulator. It means that it has unique physical properties somewhere in between a conductor like aluminum and an insulator like glass. In a process called doping, small amounts of impurities are added to pure semiconductors causing large changes in the conductivity of the material. Examples include silicon, the basic material used in the integrated circuit, and germanium, the semiconductor used for the first transistors.

Importance

To understand the importance of semiconductors let's first understand the difference between electricity and electronics. Both are concerned with generating, transferring, and utilizing electrical energy. The chief difference is that electricity is concerned with using that electrical energy in power applications for heat, light, and motors while electronics is concerned with power control and communications applications such as electronic thermostats, electric motor speed control and radio. Engineering importance of semiconductors results from the fact that they can be conductors as well as insulators. Semiconductors are especially important because varying conditions like temperature and impurity content can easily alter their conductivity. The combination of different semiconductor types together generates devices with special electrical properties, which allow control of electrical signals. Semiconductors are employed in the manufacture of electronic devices and integrated circuits. Imagine life without electronic devices. There would be no radios, no TV's, no computers, no video games, and poor medical diagnostic equipment.

Types of Semiconductor

Semiconductors are mainly classified into two categories: Intrinsic and Extrinsic. An intrinsic semiconductor material is chemically very pure and possesses poor conductivity. It has equal numbers of negative carriers (electrons) and positive carriers (holes). Whereas an extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, this alters the electrical properties of the semiconductor and improves its conductivity. Introducing impurities into the semiconductor materials (doping process) can control their conductivity. Doping process produces two groups of semiconductors: the negative charge conductor (n-type) and the positive charge conductor (p-type). Semiconductors are available as either elements or compounds. Silicon and Germanium are the most common elemental semiconductors. Compound Semiconductors include InSb, InAs, GaP, GaSb, GaAs, SiC, GaN. Si and Ge both have a crystalline structure called the diamond lattice. That is, each atom has its four nearest neighbors at the corners of a regular tetrahedron with the atom itself being at the center. In addition to the pure element semiconductors, many alloys and compounds are semiconductors. The advantage of compound semiconductor is that they provide the device engineer with a wide range of energy gaps and mobilities, so that materials are available with properties that meet specific requirements. Some of these semiconductors are therefore called wide band gap semiconductors.

Intrinsic Semiconductor

A silicon crystal is different from an insulator because at any temperature above absolute zero temperature, there is a finite probability that an electron in the lattice will be knocked loose from its position, leaving behind an electron deficiency called a "hole".

If a voltage is applied, then both the electron and the hole can contribute to a small current flow.

The conductivity of a semiconductor can be modeled in terms of the band theory of solids. The band model of a semiconductor suggests that at ordinary temperatures there is a finite possibility that electrons can reach the conduction band and contribute to electrical conduction.

The term intrinsic here distinguishes between the properties of pure "intrinsic" silicon and the dramatically different properties of doped n-type or p-type semiconductors.

The current which will flow in an intrinsic semiconductor consists of both electron and hole current. That is, the electrons which have been freed from their lattice positions into the conduction band can move through the material.

In addition, other electrons can hop between lattice positions to fill the vacancies left by the freed electrons. This additional mechanism is called hole conduction because it is as if the holes are migrating across the material in the direction opposite to the free electron movement.

The current flow in an intrinsic semiconductor is influenced by the density of energy states which in turn influences the electron density in the conduction band. This current is highly temperature dependent.

Extrinsic Semiconductor

Doped semiconductors (either n-type or p-type) are known as extrinsic semiconductors. The activation energy for electrons to be donated by or accepted to impurity states is usually so low that at room temperature the concentration of majority charge carriers is similar to the concentration of impurities. It should be remembered that in an extrinsic semiconductor there is an contribution to the total number of charge carriers from intrinsic electrons and holes, but at room temperature this contribution is often very small in comparison with the number of charge carriers introduced by the controlled impurity doping of the semiconductor.

If a very small number of atoms of a group V element such as phosphorus (P) are added to the silicon as substitutional atoms in the lattice, additional valence electrons are introduced into the material because each phosphorus atom has 5 valence electrons. These additional electrons are bound only weakly to their parent impurity atoms (the bonding energies are of the order of hundredths of an eV), and even at very low temperatures these electrons can be promoted into the conduction band of the semiconductor. This is often represented schematically in band diagrams by the addition of 'donor levels' just below the bottom of the conduction band, as in the schematic below.

The presence of the dotted line in this schematic does not mean that there now exist allowed energy states within the band gap. The dotted line represents the existence of additional electrons which may be easily excited into the conduction band. Semiconductors that have been doped in this way will have a surplus of electrons, and are called n-type semiconductors. In such semiconductors, electrons are the majority carriers.

Conversely, if a group III element, such as aluminium (Al), is used to substitute for some of the atoms in silicon, there will be a deficit in the number of valence electrons in the material. This introduces electron-accepting levels just above the top of the valence band, and causes more holes to be introduced into the valence band. Hence, the majority charge carriers are positive holes in this case. Semiconductors doped in this way are termed p-type semiconductors.

How Semiconductors Works?

Most of the semiconductor devices and chips are created with silicon. The commonly heard expressions like "Silicon Valley" and the "Silicon Economy" come from this fact. In the periodic table, you will find that silicon sits next to aluminum, below carbon and above germanium. Carbon, silicon and germanium have a unique property in their electron structure -- each has four electrons in its outer orbital. This allows them to form nice crystals. The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In silicon, the crystalline form is a silvery, metallic-looking substance. Metals tend to be good conductors of electricity because they usually have "free electrons" that can move easily between atoms, and electricity involves the flow of electrons. While silicon crystals look metallic, they are not, in fact, metals. All of the outer electrons in a silicon crystal are involved in perfect covalent bonds, so they can't move around. A pure silicon crystal is nearly an insulator -- very little electricity will flow through it. You can change the behavior of silicon and turn it into a conductor by doping it. In doping, you mix a small amount of an impurity into the silicon crystal. A minute amount of either N-type or P-type doping turns a silicon crystal from a good insulator into a viable (but not great) conductor -- hence the name "semiconductor."

However electrons are not the only players in the "conduction game"! Another particle plays a major role in conduction in semiconductors. What is this particle? That is also what happens when an electron in a semiconductor jumps from the valence band to the conduction band. It is called a hole. Some electrons and holes play an important role in electrical conduction in semiconductors:

Electrons have a negative charge. Holes have a positive charge. Electrons and holes are not static: they can move. Holes move more slowly than electrons. When electrons move in one direction, holes move in the opposite direction. This is like cars parked along a street. If one car moves to an empty slot, the empty slot moves the other way.

The cars move to the right, the empty slot to the left. A solitary electron in the presence of a solitary hole will recombine. Only electrons and holes which are free, and hence have not recombined, play a role in electrical conduction.

Properties of Semiconductor

Semiconductors have many useful properties that insulators and conductors do not possess. These properties are based on the fact that an electron can jump from the valence band to the conduction band and vice versa. Temperature can give this little extra energy to an electron and make it jump to the conduction band thus creating a hole in the valence band.

Light can also give this energy boost and create what we call an electron-hole pair: a free electron and a free hole: this phenomenon is called absorption. Photo conductivity is the increase of current in a semiconductor due to the absorption of photons. Light has a dual nature: it behaves as a wave and as a particle. The particle associated with light is called a photon. Photons can have different energies.

When light illuminates a semiconductor:
· the photons with the right energy are absorbed by the material
· the electrons from the valence band have enough energy to jump to the
conduction band
· the conductivity increases due to the higher number of electrons in the
conduction band.
Electroluminescence is the conversion of electrical energy into light. Let's consider electrons in the conduction band. These electrons are in an excited state: they have gained some energy to jump to the conduction band.
· they release the extra energy that they have
· this energy is emitted as a photon
Photons emitted by electroluminescence come out in random directions: this type of light is called incoherent light. For instance light from a light bulb is incoherent. Stimulated emission is a little bit like electroluminescence except that it is not a spontaneous process: the excited electron is forced into jumping back to the valence band and emitting a photon.

Such electrons eventually fall back into the valence band in a lower energy state.

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Digital Electronics

noreply@blogger.com (Unknown) — Sun, 09 Jun 2013 06:06:00 +0000

Digital electronics, or digital (electronic) circuits, represent signals by discrete bands of analog levels, rather than by a continuous range. All levels within a band represent the same signal state. Relatively small changes to the analog signal levels due to manufacturing tolerance, signal attenuation or parasitic noise do not leave the discrete envelope, and as a result are ignored by signal state sensing circuitry. In most cases the number of these states is two, and they are represented by two voltage bands: one near a reference value (typically termed as "ground" or zero volts) and a value near the supply voltage, corresponding to the "false" ("0") and "true" ("1") values of the Boolean domain respectively.

Digital techniques are useful because it is easier to get an electronic device to switch into one of a number of known states than to accurately reproduce a continuous range of values. Digital electronic circuits are usually made from large assemblies of logic gates, simple electronic representations of Boolean logic functions.

PRO’S

An advantage of digital circuits when compared to analog circuits is that signals represented digitally can be transmitted without degradation due to noise.

For example, a continuous audio signal transmitted as a sequence of 1s and 0s, can be reconstructed without error, provided the noise picked up in transmission is not enough to prevent identification of the 1s and 0s. An hour of music can be stored on a compact disc using about 6 billion binary digits.

Information storage can be easier in digital systems than in analog ones. The noise-immunity of digital systems permits data to be stored and retrieved without degradation. In an analog system, noise from aging and wear degrade the information stored. In a digital system, as long as the total noise is below a certain level, the information can be recovered perfectly.

CON’S

In some cases, digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing more heat which increases the complexity of the circuits such as the inclusion of heat sinks. In portable or battery-powered systems this can limit use of digital systems.

Digital circuits are sometimes more expensive, especially in small quantities

Digital memory and transmission systems can use techniques such as error detection and correction to use additional data to correct any errors in transmission and storage.

Passive and Active components

noreply@blogger.com (Unknown) — Sat, 08 Jun 2013 17:53:00 +0000

Passive components

Resistors

One of the most common types of passive electrical components is the resistor. Resistors come in many types, from very simple resistors that fit comfortably in a toddler’s hand and are used in high school electronics experiments, to massive resistor boxes that are used in power stations and for other industrial purposes. Resistors are useful for adjusting the current flowing through a wire. As resistance increases relative to voltage, the current in a circuit will decrease. For this reason, when electricians and engineers need to reduce the current in a circuit, they will add resistors. When designing a circuit that can pass varying currents, professionals will add a switch that allows the current to pass through multiple branches. Some of these branches will have more resistance, and some will have less. The current can be increased by pointing the switch to a branch with less resistance, and decreased by pointing it toward a branch with more resistance.

Capacitor

Another common passive circuit component is the capacitor. Capacitors store energy inside themselves when a current is passed through the circuit. Capacitors have two sides, one that is positive and one that is negative, and the two sides are separated by an insulator. This creates a voltage difference, and the resulting electrostatic field holds energy that can be harnessed by the circuit. Because capacitors are able to store energy, they are useful for moderating circuits that experience variable currents. Capacitors can store or release their energy, as necessary, to increase or decrease the current flowing through the circuit.

Inductors

These are the last of the purely passive components. An inductor is most commonly a coil, but in reality, even a straight piece of wire has inductance. Winding it into a coil simply concentrates the magnetic field, and increases the inductance considerably for a given length of wire. Although there are some very common inductive components (such as transformers, which are a special case), they are not often used in audio. Small inductors are sometimes used in the output of power amplifiers to prevent instability with capacitive loads.

Active components

Semiconductors

There are many different types of semiconductors, but just a few are outlined below. The basic principle of a semiconductor is that it is only “semi” conductive. It doesn’t allow electricity to flow through it as easily as a conductor like copper, but it permits enough electrical flow to be part of a circuit. In consequence, semiconductors are very useful for altering the properties of an electrical current, and either amplifying it, changing its voltage, or (in modern electronics) altering the signal it communicates. As noted above, there are many different types of semiconductors. Some of the most important are noted and explained below.

Diodes

Most people are familiar with “light emitting diodes,” the tiny light bulbs present on many control panels and other displays. For this reason, many think that emission of light is the key characteristic of diodes, but in fact, not all diodes emit light. Instead, the defining characteristic of a diode is that it only permits electricity to flow in one direction, but not the other. This is because the ends of a diode are polarized, and electrons will only flow across positive-negative poles in one direction, from the negative to the positive. This is useful for controlling the current in a circuit.

Transistors

Transistors use a very small current passed into one of their terminals to control the (typically larger) current flowing through their other terminals. One very useful aspect of transistors is that the current they output can be substantially larger than the current that is passed to them; this is known as amplification. Because transistors use small currents on one terminal to control larger currents on other terminals, they make great switches for machines. Buttons on electrical equipment almost always lead to transistors which then control some option within a device or control chip. Transistors are critical to modern electronics, and have been called the most important invention of the 20th century, because microchips and microcontrollers are, at their essence, just billions of transistors switching in sequence.

Integrated circuits

Integrated circuits are better known today as “chips” or “microprocessors.” They consist of one circuit substrate, with numerous electronic circuits connected to it and operating in tandem. All modern electronics use integrated circuits, or have integrated circuits somewhere within them. Integrated circuits are made up of transistors, discussed above. In general, a single integrated circuit substrate will have billions of transistors, all flicking at once to control the countless options within an electronic device.

Optoelectronic devices

Optoelectronic devices are a huge category of circuit components. The components that fall within this category do one or more of these three things: emit light, sense light, or manage components that emit/sense lights. Fiber optic devices, for one, fall into the category of optoelectronic devices. The same goes for various diodes that do have the property of emitting light. But not only things that laypeople would recognize as “light bulbs” fall into this category. Just as importantly, there are lots of electronic components that are designed to detect light without ever emitting it themselves. Through complex physical reactions, light detectors can actually introduce electricity into a circuit, which is why they qualify as active circuit components.

Do you know the Basic Definitions?

noreply@blogger.com (Unknown) — Sat, 08 Jun 2013 16:56:00 +0000

The basic electrical units and definitions are as shown below. This list is not exhaustive (also see the Glossary), but covers the terms you will encounter most of the time. Many of the terms are somewhat inter-related, so you need to read all of them to make sure that you understand the relationship between them.

Passive: Capable of operating without an external power source.

Typical passive components are resistors, capacitors, inductors and diodes (although the latter are a special case).

Active: Requiring a source of power to operate.

Includes transistors (all types), integrated circuits (all types), TRIACs, SCRs, LEDs, etc.

DC: Direct Current

The electrons flow in one direction only. Current flow is from negative to positive, although it is often more convenient to think of it as from positive to negative. This is sometimes referred to as "conventional" current as opposed to electron flow.

AC: Alternating Current

The electrons flow in both directions in a cyclic manner - first one way, then the other. The rate of change of direction determines the frequency, measured in Hertz (cycles per second).

Frequency: Unit is Hertz, Symbol is Hz, old symbol was cps (cycles per second)

A complete cycle is completed when the AC signal has gone from zero volts to one extreme, back through zero volts to the opposite extreme, and returned to zero. The accepted audio range is from 20Hz to 20,000Hz. The number of times the signal completes a complete cycle in one second is the frequency.

Voltage: Unit is Volts, Symbol is V or U, old symbol was E

Voltage is the "pressure" of electricity, or "electromotive force" (hence the old term E). A 9V battery has a voltage of 9V DC, and may be positive or negative depending on the terminal that is used as the reference. The mains has a voltage of 220, 240 or 110V depending where you live - this is AC, and alternates between positive and negative values. Voltage is also commonly measured in millivolts (mV), and 1,000 mV is 1V. Microvolts (uV) and nanovolts (nV) are also used.

Current: Unit is Amperes (Amps), Symbol is I

Current is the flow of electricity (electrons). No current flows between the terminals of a battery or other voltage supply unless a load is connected. The magnitude of the current is determined by the available voltage, and the resistance (or impedance) of the load and the power source. Current can be AC or DC, positive or negative, depending upon the reference. For electronics, current may also be measured in mA (milliamps) - 1,000 mA is 1A. Nanoamps (nA) are also used in some cases.

Resistance: Unit is Ohms, Symbol is R or Ω

Resistance is a measure of how easily (or with what difficulty) electrons will flow through the device. Copper wire has a very low resistance, so a small voltage will allow a large current to flow. Likewise, the plastic insulation has a very high resistance, and prevents current from flowing from one wire to those adjacent. Resistors have a defined resistance, so the current can be calculated for any voltage. Resistance in passive devices is always positive (i.e. > 0)

Capacitance: Unit is Farads, Symbol is C

Capacitance is a measure of stored charge. Unlike a battery, a capacitor stores a charge electrostatically rather than chemically, and reacts much faster. A capacitor passes AC, but will not pass DC (at least for all practical purposes). The reactance or AC resistance (called impedance) of a capacitor depends on its value and the frequency of the AC signal. Capacitance is always a positive value.

Inductance: Unit is Henrys; Symbol is H or L (depending on context)

Inductance occurs in any piece of conducting material, but is wound into a coil to be useful. An inductor stores a charge magnetically, and presents a low impedance to DC (theoretically zero), and a higher impedance to AC dependent on the value of inductance and the frequency. In this respect it is the electrical opposite of a capacitor. Inductance is always a positive value. The symbol "Hy" is sometimes used in (guess where :-) ... the US. There is no such symbol.

Impedance: Unit is Ohms, Symbol is Ω or Z

Unlike resistance, impedance is a frequency dependent value, and is specified for AC signals. Impedance is made up of a combination of resistance, capacitance, and/ or inductance. In many cases, impedance and resistance are the same (a resistor for example). Impedance is most commonly positive (like resistance), but can be negative with some components or circuit arrangements.

Decibels: Unit is Bel, but because this is large, deci-Bels (1/10th Bel) are used), Symbol is dB

Decibels are used in audio because they are a logarithmic measure of voltage, current or power, and correspond well to the response of the ear. A 3dB change is half or double the power (0.707 or 1.414 times voltage or current respectively). Decibels will be discussed more thoroughly in a separate section.

A few basic rules that electrical circuits always follow are useful before we start.

The current entering any passive circuit equals the current leaving it, regardless of the component configuration.
Electricity can kill you!
The danger of electricity is current flowing through your body, not what is available from the source. A million volts at 1 micro amp will make you jump, but 50V at 50mA can stop you dead - literally.
An electric current flowing in a circuit does not cause vibrations at the physical level (good or bad), unless the circuit is a vibrator, loudspeaker, motor or some other electro-mechanical device. (i.e. components don't vibrate of their own accord unless designed to do so.)
External vibrations do not affect the operation of 99.9% of electronic circuits, unless of a significant magnitude to cause physical damage or the equipment is designed to detect such vibrations (for example, a microphone).
Power is measured in Watts, and PMPO does not exist except in the minds of advertising writers.
Large capacitors are not intrinsically "slower" than small ones (of the same type). Large values take longer to charge and discharge, but will pass AC just as well as small ones. They are better for low frequencies.
Electricity can still kill you, even after reading this article

Electronic components

noreply@blogger.com (Unknown) — Sat, 08 Jun 2013 15:03:00 +0000

An electronic component is any physical entity in an electronic system used to affect the

electrons or their associated fields in a manner consistent with the intended function of the electronic system. Components are generally intended to be connected together, usually by being soldered to a printed circuit board (PCB), to create an electronic circuit with a particular function (for example an amplifier, radio receiver, or oscillator). Components may be packaged singly, or in more complex groups as integrated circuits. Some common electronic components are capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as active (e.g. transistors and thyristors) or passive (e.g. resistors and capacitors).

Passive components

Passive components can't introduce net energy into the circuit. They also can't rely on a source of power, except for what is available from the (AC) circuit they are connected to. As a consequence they can't amplify (increase the power of a signal), although they may increase a voltage or current (such as is done by a transformer or resonant circuit). Passive components include two-terminal components such as resistors, capacitors, inductors, and transformers.

In electrical, computer or storage systems, passive components are those that do not require electrical power to operate (e.g., not capable of power gain). This could include the chassis, capacitors, resistors or enclosures that do not require electrical power to operate.

E.g. Resistors, Capacitors, Magnetic (inductive) devices, Networks, Transducers, sensors, detectors, Antennas

Active components

Active components are the parts of a circuit that absolutely need a power source to function. These components can increase the electricity in a circuit, though they do not always do so. It is possible that they have a power source in addition to the alternating current flowing through the circuit, though it is not critical that they have one. Ultimately, the key aspect of active components is that they can produce a net increase in the electricity in a circuit, though they do not have to.

E.g. Semiconductors, Diodes, Transistors, Integrated circuits, Optoelectronic device

For a better understanding of Active components, Passive components look over the list of components which follows on other pages.

Do You Know About Electronics?

noreply@blogger.com (Unknown) — Sat, 08 Jun 2013 14:00:00 +0000

Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies. The nonlinear behavior of active components and their ability to control electron flows makes amplification of weak signals possible and electronics is widely used in information processing, telecommunications, and signal processing. The ability of electronic devices to act as switches makes digital information processing possible. Interconnection technologies such as circuit boards, electronics packaging technology, and other varied forms of communication infrastructure complete circuit functionality and transform the mixed components into a regular working system.

Electronics is distinct from electrical and electro-mechanical science and technology, which deals with the generation, distribution, switching, storage, and conversion of electrical energy to and from other energy forms using wires, motors, generators, batteries, switches, relays, transformers, resistors, and other passive components. This distinction started around 1906 with the invention by Lee De Forest of the triode, which made electrical amplification of weak radio signals and audio signals possible with a non-mechanical device. Until 1950 this field was called "radio technology" because its principal application was the design and theory of radio transmitters, receivers, and vacuum tubes.

Today, most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solid state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This article focuses on engineering aspects of electronics.

Source: wikipedia

noreply@blogger.com (Unknown) — Fri, 07 Jun 2013 16:14:00 +0000

This site is a free online book that teaches analog and digital electronics using interactive animations.You can also download free e-books.