Circuit Sector

1Hz Clock Generator Circuit Using COB

2012-01-27T20:52:00.002+05:30

Let's familiarize with a COB - chip on board device by building a precision 1Hz clock generator. Circuits that usually generate 1Hz clock makes use of ICs with variable capacitors but they are not very precise. ( micro controller based one should be precise but it costs large ). better accuracy can be obtained by a COB found inside a digital clock, which is cheaply available in the market.

1Hz clock generator circuit diagram : Click on the image to enlarge

The COB is a small pcb consist of an IC chip capacitors and quartz crystal, etc. Here's the some important points to note before you assemble the clock generator.

R1, C3, diodes D1 and D2 shown in the circuit convert 5V DC into 1.4V DC which is the supply voltage to the COB.
A ½Hz clock is available at terminals A and B with a phase difference of 90o, these pins are coupled using capacitors C1 and C2 to obtain a complete 1Hz clock.
Op-amp IC CA3140 used to amplify the output of the COB to a considerable level.
R4 and R3 is used to set the gain of the op-amp.
T1 and T2 transistors further amplifies the clock output to drive the digital clocks and timers.
Preset VR1 is offset null control used to adjust proper 1Hz pulse at the output terminal ‘E’.
LED blinks every one second interval.

Visitor Alarm Secret Bell

2012-01-08T20:34:00.001+05:30

This circuit can acts as a visitors alarm as well as a secret bell which can be used to identify family members. If you'e living in flats, it'll become necessary to verify the visitor before opening the door. This circuit senses single puff of breath and activates a musical bell automatically.

Working of the circuit

The core of this simple circuit has an NE555 timer and a well-known UM-66 musical IC. You need to fit the condenser mic inside the existing calling bell switch. Obviously, the mic will sense the air pressure changes following the breath. So it can trigger the alarm. On the other side, only you family members know about this system, hence they puff out before the hole, the door can be opened without any hesitation.

The BC 549 transistor act as an amplifier to boost the sinals received from the mic, it triggers the monostable wired NE555 IC. The power from this IC1 will trigger IC2 UM66 which generate music tone for a short period of time. The monostable timing period can be set by resistor R7 and capacitor C5.

LED Running Display Using NE555

2011-12-15T18:41:00.001+05:30

Here's a circuit to build a led based running display using easily available general purpose timer IC NE555 and a popular decade counter IC CD4017. This display consist of 24 LED's of four layers. The NE555 is wired as an astable multivibrator whose output triggers CD4017 counter.

Circuit diagram of LED based running effect display.

On powering up the circuit, timer starts oscillates to produce triggering pulses. This pulses trigger counter IC and it counts from 0 to 5. These outputs are fed to general purpose NPN transistors BC547 which are used as current drivers for each led layer. As each of the counter output goes hih, the curresponding led layer glows sequentially. After it counts upto 6 values, resets to zero and the process repeats.

How to display custom words using this circuit.

Suppose you want to display ‘STAR.’ Build letter S with L1,T with L2, A with L3 and R with L4.When the circuit is switched on, letter S glows first. Then S and T glow sequentially,followed by S, T and A, and thenS, T, A and R. When Q4 and Q5 outputs of the counter gohigh, the completeword ‘STAR’ glows.Thereafter, letter ‘S’glows again and the cycle repeats.

Dual power supply from single battery supply

2011-12-02T19:42:00.001+05:30

Dual power supply is a very essential part in the laboratory or in your work while there you use op-amps in your circuit. Most of the opamp Ic's require dual voltage supply. But it's difficult to provide dual power supply as it's costlier than a single battery.

Circuit diagram of Dual power supply from single battery: Click on image to enlarge

Here's circuit that provide both +9V and -9V from single 9V battery. It consist of the basic timer NE555 and a negative voltage regulator IC LM7909 as main parts. The boosted voltage is made ripple free by the negaive voltage regulator.

The timer IC is configured as a astable multivibrator of 100KHz frequency and is boosted using a villard cascade voltage multiplier. As the output frequency of the multivibrator is far beyond the AF range, it will not picked up by the audio amplifiers and other devices working in the AF range.

CCFL Tester Circuit For LCD Screens

2011-10-06T21:45:00.000+05:30

Lcd's cover a wide range of applications including led tv's to cmputer monitors, PDAs, digital monitors and much more. LCD backlight mainly consists of a light source, diaphragm, light leading board and a plastic frame. Cold-cathode fluorescent lamps (CCFLs) have a phosphor coated glass cylinder with cathodes at each end. The CCFL inverter accepts a low-level DC input voltage and provides a high-level AC output to run the backlight CCFL tube. Here's a CCFL tester circuit that often needed to check a faulty LCD backlight circuit for finding the dead components.

Circuit schematic of CCFL tester.

The ciruit is portable6V battery operated and can be used to test almost all types of LCD backlight CCFL tubes.Here the NE555 timer IC is working as an astable multivibrator. This drives to drive a standard MOSFET T1 (IRF 512/IRF 830). Here an ordinary step-down transformer is used as the inverter transformer by reversing its primary and secondary windings.

Get Electronics For You Magazine For 2 Years at Rs. 590

2011-08-30T11:34:00.000+05:30

The south Asia's most popular electronics magazine is now with their evergreen offer for readers labelled, Pay for 1 year and get 2 years. you can subscribe to the EFY and save 50% of the actual price of this magazine. This offer is available for new customers as well as renewal for existing customers.

Method of subscription and payment:

Electronics for you magazine 2 years / 24 issues (with cd) - RS.590

To make online payment with net banking or credit card, click here
To download order form, click here (payment through cheque/DD/MO)

Note: This offer is valid only for Indian customers. Please allow up to 4-6 weeks to process subscription.

Low Cost Hearing Aid Circuit

2011-07-30T18:33:00.000+05:30

This can also be called a poor man's hearing aid because it can be constructed from some low cost components although its performance is not comparable to that of commercially available sophisticated hearing aids, still it can serve the purpose well for persons with a low degree of hearing impairment.

Circuit Diagram Of Low cost hearing aid

This circuit utilizes two Sanyo’s MSI (medium- scale-integrated) surface-mount 10-pin DIL IC LA4537M
which have been cascaded to improve gain and sensitivity in most audible range. With 3V supply voltage, you can afford to use 1/8-watt resistors, while the electrolytic capacitors’ voltage rating can be as low as 5V. This will allow the assembled circuit to occupy very little space. Apart from the usual battery ‘on’/‘off’ switch S1, muting ‘on’/‘off’ switch S2 has also been provided. Both S1 and S2 could be PCB-mount slide switches.

Simple Floor Mat Switch

2011-06-30T19:57:00.000+05:30

This cool 555 IC circuit produces a warning beep when some one enters or crosses the prohibited area in your house or office. The switch can be hidden under floor mat, triggers the circuits to produce a beep when someone presses it by foot.

Circuit diagram of mat switch

The switch that place under mat is of two conductive foam. It can be constructed by using two thin metal foils gummed together on opposite sides of a card board. When the circuit switch is open, the transistor T1 is on off state since the lack of forward biasing at the base. When the switch closes by a an external object, T1 will be on and it's collector voltage drops. This acts as a trigger input for IC 555.

Sound is produced for 50 seconds with preset values of R4 and C3. the pulse is applied through transistor T2. The duration of pulse can be changed by changing the values of R4 and C3.

LED Lighting Product Design

2011-06-18T10:05:00.000+05:30

The performance of led's has improved so much over time that these tiny bulbs aare all set to brighten our home, offices, buildings, light up streets, use in LED projector mobile phones, and they get involved in our lives in very interesting ways. Goverments are challenging companies to come up with viable, sustainable, LED-based home lighting solution not only for saving energy also to increase our lighting standards. LED- based home lighting solutions are cheap enough to replace a 60W incandescent lamp. Eco-friendly, low power led lamps might be the biggest step we take towards saving this planet.

Engineers involved in designing innovative and affordable LED lighting solutions can now benefit from a board product portfolio of LED drivers AC/DC power management devices, wired and wireless control and embedded processors. These products have an options to controlling power stages of LED lighting but also need to control LED currents. These eliminating the need of multiple components and reducing system cost.

The reliability of LED drivers is a crucial factor to achieve longer life expectations. While designing an LED driver, we need to taken care of component selection. LED lighting systems can be desiggned to accurately control voltage and current regulations for precise LED light intensity and colour mixing, temperature monitoring to prevent thermal runaway, intelligent and adaptive dimming of the LED and fault detection on over voltage or current, blown string. Communications with external systems are also possible via power line communication (PLC), wireless technology or interfaces.

Simplest Transistor Tester Circuit

2011-06-15T22:24:00.000+05:30

This simple-to-construct transistor tester circuit is useful for testing both npn and pnp low-power transistors. It comprises a few resistors, LEDs, diodes, and a mains step-down transformer. The 230V mains voltage is stepped down to about 6 volts before applying to the circuit. The leads of transistor under test are inserted in the test terminals (sockets) marked E, B, and C (for emitter, base, and collector, respectively) appropriately, i.e. the emitter of the transistor is to be inserted in terminal E, the base of the transistor in terminal B, and the collector of the transistor in terminal C.

Circuit diagram of Transistor Tester : Click on image to enlarge

The resistor to be connected in series with the base terminal is selected with the help of a 6-position rotary switch S1 as per base current requirement for the transistor. Two different coloured (green and red) LEDs are used for indication. Green LED glows if the npn transistor under test is good, otherwise not. Likewise, when a pnp transistor is tested, the glowing of red LED indicates that the transistor is good and no glowing indicates that the transistor is bad.

Laser Communication System Circuit

2011-06-09T10:29:00.000+05:30

In a laser communication system, the information signal such as sound or music is transmits through a laser beam. the intensity of the laser beam changes with respect to amplitude of the laser beam which is the modulation process. In the receiver circuit a solar panel is used to reproduce the desired voltage level. The voltage variation on the solar panel is amplified by a low-voltage audio power amplifier LM386 which has a volatge gain of 20 to 200 and reproduced by a speaker.

This Laser communication system has main two parts:

1. Laser transmitter Circuit

2. Laser receiver circuit

Both the transmitter and the receiver are built around IC LM386, powered by a 9V battery. In transmitter circuit, a laser diode (LD1) with maximum operating voltage of around 2.6V DC and maximum operating current of 45 mA is used to transmit the audio signal. The voltage divider network formed by R2, R3 and VR3 keeps the voltage as well as the current for the laser diode in the safe region. A laser pointer can also be used in place of a laser diode.

Potentiometer VR1 (10-kilo-ohm) is used to change the level of the input audio signal. The audio input (Vin) is taken from the preamplifier output of the music system (CD player, DVD player, etc). Capacitor C2 and preset VR2 are used to vary the gain of the LM386.

The receiver circuit is shown in the figure. The audio signal transmitted by the laser diode (LD1) is received by the calculator’s solar panel and amplified by IC2. The gain of the amplifier is fixed by capacitor C7. Preset VR4 is used to change the signal level from the solar panel. This signal is fed to input pin 3 of IC2 through coupling capacitor C5 so that the DC value from the solar panel can be eliminated. The amplified output from IC2 is fed to the speaker, which plays the music from the CD player connected at the input (Vin) of IC1.

Two seperate PCBs can be used to assemble transmitter and receiver circuit and enclose in two cabinets. Make an arrangement such as the laserbeam from diode falls directly on the solar panel.

Ambient Electronics - Characteristics and Opportunities

2011-05-27T19:42:00.000+05:30

Research on miniaturization of hardware, information processing, wireless communication, human machine interfaces etc is taking us closer to the ambient electronics future. Ambient electronics will ley you to make a smart home by tomorrow. The lights switch on when you enter the room and turn off automatically when you leave. The doors automatically opens and closes by detecting proximity of human. Your alarm time will be automatically adjusted to internet time and give you today's weather forecast when you get up and the scope of ambient electronics is unimaginable.

Siemens Home automation

Without taking you to the complexities, here's the list of some of the advantages of ambient electronics:

Unobtrusive
Adaptable
Secure
Human-centric interfaces
Context aware
Personalised
Anticipatory
Highly network capable
Calm

These Key characteristics of ambient electronics makes it a wide field with numerous opportunities like:

RFID
Wi-Fi
Bluetooth
Near field communications
Home area networking
Embedded electronics
PCB development
Embedded operating systems and software
Voice recognition
Internet infrastructure
Flat displays like LCD's
Miniaturization
System In package

Best 5 Robotics Engineering Websites to Learn and Discuss

2011-05-22T13:25:00.005+05:30

Robotics, a technology that combines knowledge of electronics, mechanical and software engineering is the most exciting field today. There are some really cool projects and applications using robots. Here are some best websites for all robot enthusiasts as well as college students in engineering courses.

Go Robotics

This website started in 1998, is one of the most interesting websites on robotics. it has some really cool videos, circuit ideas and descriptions on how to build a robot from scratch and robotic gift ideas. This website has been mostly liked by hobbyists who play around with open source and do it yourself projects, it is linked on social networks and has developed an online community to regularly contribute, work together and have fun with robotics.

Robotics India

It is an online forum that connects the robotics enthusiasts in india. You can post an announcement, news or start discussion on any topic based on robots. The online community helps you to develop your robotic projects much faster by providing you information on what's new, world's news, blogs etc. You can register yourself online.

Seattle Robotics

The encoder page of this website lists the with 'home-built' robot information on how the projects can be started and finished. Here' you may get ideas on how a machine actually moves or does something. The list includes the name of the robotics projects. A brief description and link to its home page. It is a modest collection of cool places where you can see what people are doing and in many cases how they did it.

NASA Robotics Page

The robotics alliance project of national aeronautics and space admisnistration (NASA) aims at creating a human, technical and programmatic resource of robotics capabilities to enable implementation of future robotics space exploration missions. Although the objective of this page is to support ameracan development and inspire high school students to pursue robotics.

Society of Robots

It is a very resourceful collection of information on robotics books, projects tutorials and journals. It has different categories to give you in-depth information on the skills and hardware like microcontrollers, sensors,actuators, batteries etc. The small robotic projects like 50$ robot will be an excellent choice for a beginner to start with robotics.

LPG Gas Leakage Alarm Circuit

2011-05-20T21:57:00.000+05:30

All of us aware of the danger while handling the LPG gas cylinders which uses in the kitchen or in the motor vehicles. LPG gas is supplied in pressurized steel cylinders. When the gas leakes from a cylinder, it it flows along floor and tends to settle down in low spots of the room, because the LPG is heavier than air. If not properly exhausted, this can cause, fire or suffocation.

Fig. 1: Circuit for gas leakage alarm

Fig. 2: Pin details of gas
sensor module

Here is an electronic circuit that detects LPG presence and alert the user through LED and speaker alarm. The circuit is based on the 555 timer IC which is available easily. A 9V battery can be used to operate this equipment and the zenar diode used cover the supply to 5V dc. This drives the LPG gas sensor module SEN-1327 from RhydoLABZ. This is an active high device, which means the output goes high when the gas level exceeds a minimum level in the vicinity.

The Gas detector is sensitive to propane, butane, isobutene, LPG and natural gas as per the data sheet. It can also be used to detect combustible gas mainly methane.

Threshold LPG concentration : 1000 ppm

The multivibrator basically works as a tone generator which is triggered by the high output of the gas sensor module. The pitch of the tone can be changed by varying preset VR1. Use a suitable heat-sink for transistor SL100.

Tips to find and repair a dry solder joint

2011-05-19T11:01:00.000+05:30

Many electronic equipments often caught with an illness called dry solder joints or dry solder in short. What are they? and how can be spotted in a printed circuit board(PCB) are the main purpose of this post.

As the name suggests dry solder joints are legitimate faults in electronics equipment. It mainly causes due to poor soldering practices and the physical conditions at which the equipment held.The below image explain how a bad soldering results in a dry joint.

Dry solders are more likely to be found on amplifiers, CRT monitors, Television sets and devices and equipments which the PCB has to hold massive devices such as transformers and LOT's etc. Main causes of dry joints are vibration, poor soldering and bad PCB.

Dry solder joint symptoms

If the equipment has dry joint on its PCB it stops working completely or shows inconsistency with its operation. For example, a CRT monitor may suffer vertical or horizontal shrinking, over brightness etc The fun part is that if you shake or knock the body, it will contiue to its normal operation.

How to spot a Dry joint on a CRT monitor

Opens up the cover and take PCB out for inspection. The better way to find a dry joint is to visually inspect the solder joints. The below pictures will teach you how to spot a dry joint. Use a torch to watch care fully the solder side to find the faulty joints.

Using Toothbrush: You can use a dry tooth brush to do this job. For this, turn your equipment on(monitor) and rub slightly on the solder side. When the area of PCB where dry joint fault were rubbed, you will see appropriate responses on the screen or in working of that device.

How to fix a Dry solder Joint

When the faul joint is found, heat the solder up and remove it. Put some soldering paste(flux) and resolder that joint carefully until the solder becomes shiny. The blow image shows a good soldering.

Download MPLAB examples ASM - PIC Programming

2011-05-07T08:36:00.000+05:30

Here the basic and simple examples in assembly language written for PIC 16F877A. This includes some basic programs for lab practicals and may be useful for a PIC beginner.

Debugger: MPLAB SIM

The Download includes example programs for:

Average of two numbers
Binary counter - decade counter
Clearing of bits
Compliment of a number
Division of two numbers
Blink LED on port D
Memory location filling - Block transfer
Multiplication of two numbers
Nibble exchange
Subtraction of number
Sum of first N numbers
Two byte addition

Download ALL

Stable 455Khz BFO circuit for SSB reception

2011-04-10T22:59:00.000+05:30

Most Indian amateur radio operators prefer to operate on SSB (single sideband) and CW because these carry the signal over a long distance for a given transmitter power. Broadcast receivers are not meant to directly receive Morse code transmission on SSB and CW. Short-wave listeners require some arrangement to receive the same. One such arrangement comprises a simple IF BFO (beat frequency oscillator), which is an RF oscillator of conventional type. The output of BFO is heterodyned to beat with another frequency to obtain a resultant frequency (difference of the two frequencies) lying in the audio range (about 1 kHz).

Circuit diagram of Stable 455Khz BFO : Click on image to enlarge

BFO can be used to get an audio note from CW reception and also to resolve SSB signals. An SSB signal is transmitted without carrier signal. In ordinary receivers, it does not produce speech with sufficient clarity. When BFO signal is heterodyned with SSB signal, this RF acts like a carrier and the signal is well resolved.

The BFO circuit comprises transistors T1 and T2, which are connected in a straightforward two-stage, direct-coupled, common-emitter configuration. The input and output are in phase and positive feedback between the two is provided by ceramic filter CF1. A significant amount of feedback is provided only at the operating frequency of the filter, which is 455 kHz. So the circuit oscillates at this frequency. The ceramic filter gives good frequency stability and requires no adjustment in order to produce the correct frequency. This BFO is meant for singlesideband reception only. There is no need to connect BFO to receiver. Tune your BC receiver to any SSB signal, and then on keeping BFO just close to it, you may notice some hissing noise in your receiver. Match BFO frequency to your receiver’s IF, which may be between 452 and 460 kHz, until you get clear sound. If the BFO signal is too strong, increase the distance between BFO and receiver

Simple water level indicator with alarm

2011-04-10T22:47:00.000+05:30

This water level indicator-cum alarm circuit is built around the popular CMOS input-compatible, 7-channel IC ULN2004 Darlington array. This simple circuit setup sounds a piezo-buzzer whenever the water level in the tank rise over a certain level by adjusting the probs. This helps to turn off the electric pump to save energy and water. The 7 LED's will glow sequentially as the water rise in tank. This helps better understanding of water level in side the tank.

Circuit diagram of Simple water level indicator with alarm : Click on image to enlarge

As the water level rises in the tank, it comes in contact with probes P1 through P7 and thereby makes IC ULN2004 pins 7 through 1 high, sequentially. As a result, the corresponding output pins 10 through 16 go low one after the other, and LED1 through LED7 light up in that order. When water comes in contact with the last probe P7, it results in sounding of the piezo-buzzer connected to output pin 16 along with LED7.

Automatic heat detector alarm

2011-03-02T11:52:00.000+05:30

This heat detector circuit design uses uses a complementary comprising npn metallic transistor pair T1 (BC109) and pnp germanium transistor T2 (AC188) to detect heat (due to outbreak of fire, etc) in the vicinity and energise a siren. The collector of transistor T1 is connected to the base of transistor T2, while the collector of transistor T2 is connected to relay RL1.

Circuit diagram of Automatic heat detector : Click on image to enlarge

This temperature sensor circuit uses a popular IC UM3561 (a siren and machine-gun sound generator IC), which can produce the sound of a fire-brigade siren.The 7 and 8th pin of the IC usesd to set the inbuilt oscillator frequency. The output of the IC is pin 3.

Two darlington pair transistors (BC147&BC187) are included in this circuit to amplify the signals from the IC since the ic UM3561 is not capable to drive the speaker.

Testing the circuit

To test the working of the circuit, bring a burning matchstick close to transistor T1 (BC109), which causes the resistance of its emitter-collector junction to go low due to a rise in temperature and it starts conducting. In the same time, transistor T2 will also conducts because its base is connected to the collector of transistor T1. As a result, relay RL1 energizes and switches on the siren circuit to produce loud siren.

Tips to Extend Life Of Solar SMF Battery

2011-02-20T18:31:00.000+05:30

Off-grid photo voltaic solar power equipment require a battery to store the energy accumulated during sunny hours for use at night. In most applications lead acid batteries are proffered as these are maintenance-free and do not emitany harmful gas while charging.

When fresh charging fails due to successive cloudy days, you may end up discharging your solar smf battery deeply and thus drastically reducing its life. This can be avoided if the battery has automatic protection agains deep discharge.

The life of a lead acid battery depends on, and is directly related to how deeply the battery is discharged. For instance, a 12V, 40ah battery can ideally store 12*40=480 Wh of energy, but to avoid damaging the battery or drastically reducing its life, you should not extract all its stored energy.

When the battery is discharged, its terminal voltage starts falling. You should stop discharging the battery when the terminal voltage reaches 10.5V minimum. The battery will certainly be damaged irreversibly if it is discharged any further.

Some batteries come with automatic protection against deep discharging. In these batteries discharging beyond a limit is prevented unless battery is recharged. This feature is especially useful for solar use at home since home users cannot detect whether they are discharging the SMF battery too deeply.

The charge-discharge cycle life of a sealed lead-acid battery is also directly related to its repetitive discharge rate. In solar applications, the battery is charged onceevery sunny day. So one day is one charge discharge cycle and the battery will provide good service for:

200 to 220 days (one year) with 100 percent depth of discharge (full discharge)
400 to 450 days (two years) with 50 percent depth of discharge (partial discharge)
1000 days (four years) with 30 percent depth of of discharge (shallow discharge)
1500 days (six years) with 15 percent depth of of discharge (rated discharge)

There are SMF batteries available for solar use which come with integral protection to assure four to five years of minimum battery life.

5 Free Electronic Circuit Simulators Download

2011-02-14T22:43:00.000+05:30

Efficiency of any electronic circuits can always be improved by simulating it before actually building to pcb or general board. The best method to check a design in electronics is to use a circuit simulator and make a simple model of it to see how it works before assembling the real circuit. Electronic circuit simulation tools use mathematical models to replicate the behavior of an actual electronic device or circuit. Here are some freeware tools that will allow you to replicate the behaviour of an actual electronic circuit. All these circuit simulators suggested here are free to download.

1. Electric 8

It's an open-source electronic design automation (EDA) system that can handle many forms of circuit design and simulation. This software features include custom IC layout, schematic capture (digital and analogue), and textual languages such as VHDL and Verilog. The Electric VLSI design system is a highly flexible system that can handle many different types of electronic circuit design. Layout is done by placing and wiring electrical components. Electric comes with a built-in 12-state switch-level simulator, called ALS. The simulator displays waveforms in a separate window and lets users cross-probe from either the waveform or the circuit window.

Download Electric

2. Logisim

Logisim is an opensource educational tool for designing and simulating digital logic circuits. It has the capacity to build larger circuits from smaller sub-circuits, and to draw bundles of wires with a single mouse drag, Logisim can be used to design and simulate entire CPUs for educational purposes. Its simple user interface and simulation of circuits as you build them, make it a tool that is simple enough to learn the most basic concepts of logic circuits.

Download Logisim

3. Ngspice

Ngspice is a mixed-level/mixed-signal freeware open source circuit simulator. Its code is based on three software packages: Spice3f5, Cider1b1 and Xspice. Ngspice is part of gEDA project--a full GPL'd suite of electronic design automation tools.

Download Ngspice

4. Simulo v2.5

Simulo is a digital circuit. It's easy to use and is designed for students and hobbyists. This program is made by Benjamin Gentner.

Note: Requires .NET 3.5

Download Simulo v2.5

5. Qucs

Quite universal circuit simulator (Qucs) is an open source electronics circuit simulator software mainly for students. The software aims to support all kinds of circuit simulation types, e.g. DC, AC, S-parameter, transient, noise and harmonic balance analysis. Pure VLSI digital simulations are also supported using VHDL and/or Verilog.

Dwonload Qucs

Phase Locked Loop (PLL) Block Diagram and Applications

2011-02-11T22:02:00.000+05:30

PLL is a closed loop system designed to lock the output frequency and phase of to the frequency and phase off an input signal. The Phase Locked Loop is an important building block of linear systems.

PLL Block Diagram

PLL Explanation Of Block Diagram

The block schematic showing operating priciple of PLL is shown in figure above. It consist of

Phase Detectors
Low pass filter
DC amplifiers
Voltage controlled Oscillator(VCO)

Phase Detector

Phase detector is a comparator that compares the input frequency fs with output frequency of VCO and generates a d.c voltage that is proportional to the phase difference between the two frequencies. This dc voltage is called the error voltage. The d.c output voltage from phase detector becomes maximum when phase difference between the two frequencies (fs and fo) is pi radians or 180 degree. Without input signal, the error voltage is zero and VCO operates at set frequency fr called free running frequency of the VCO.

The phase detector is basically a multiplier and produces the sum(fs+fo) and difference (fs-fo) components at its output.

Low-pass filter

The function of the low pass filter is to remove high frequency components (fo+fs) from the output of the phase detector. This low pass filter controls the dynamic characteristics of the PLL including bandwidth, cature range, lock range and transient response.

D.C Amplifier

The D.C error voltage from the output of the low pass filter is applied to the input of a dc amplifier. Dc amplifier amplifies the error voltage level required to control the oscillations of VCO.

VCO (Voltage controlled Oscillator)

The VCO is an oscillator circuit in which the frequency of oscillation can be controlled by an externally applied voltage. The amplified d.c voltage Vc from the dc amp is applied as the control voltage to the VCO. The output frequency of VCO is directly proportional to the input d.c level of the error voltage. The error voltage Vc shifts the VCO frequency in a direction to reduce the difference in frequency between fs and fo. The VCO continues to change frequency till its output frequency fo exactly the same as the input signal frequency fs. The circuit is then said to be locked.

PLL 556 VCO Applications

FM modulation
Signal generation
Function generation
Frequency shift keying
Tone generation

Dew - Point Sensor

2011-02-09T21:01:00.001+05:30

Dew-point sensors are used in sensitive electronic equipments like cameras and copiers etc, to protect them from moisture failure by fast detection of dew. You can easily build one yourself using the readily-available dew sensor element as described in the circuit or you can use the tiny dew sensor module from your old video camera or VCR.

Circuit diagram of Dew - Point Sensor: Click on image to enlarge

The working of the dew sensor element (DS1) is based on the change in resistance of a conductive polymer in a thin film on a small ceramic substrate.When the sensing polymer becomes wet by dew, its resistance increases drastically because the polymer expands to increase the distance between the conductive particles.

This simple but highly responsive dew sensor circuit to protect equipment from dew (condensed moisture) can also be used to prevent condensation on surfaces like cold water pipes and windows. In the circuit, the dew sensor element (DS1) is connected to inverting input pin 2 of op-amp UA741 (IC1). Resistors R2 and R3 and VR1 pot provide the reference voltage at the non-inverting input pin 3 of the opamp. When a high humidity is detected, the output of IC1 changes state to switch on galvanic-isolator IC 4N35 (IC2) through optocoupler transistor driver BC337 (T1).

Adjust preset VR1 so that IC2 is disabled when the dew sensor (DS1) detects low humidity and enabled when humidity is high. This circuit can works on 12V dc power can be derived from mains.

Credits: electronicsforu

How to Enable PC Parallel Port For C programs

2011-02-06T20:12:00.001+05:30

Usually we need parallel port of our pc to interface with several circuits. Many of these projects will use C programs for its working. (for example, stepper motor control using PC) It's quite easy to write programs to access parallel port bits using C but in windows Xp you may experience problems to get correct binary output voltages by just running the program.

If you're not getting the desired output or always getting voltages like 3.3V in all pins, you should try this. Download Userport software from here. After downloading this tool, you need to copy userport.sys file to windows directory:

C:\WINDOWS\system32\drivers\

The driver gives user mode program access to selected ports by changing the x86-processors IOPM (I/O Permission Map).

Now run userport and click start, run you application C program, you should now get the correct output voltage at the data pin of PC parallel port.

12V, 3A Power Supply Using CA3085

2011-01-21T17:15:00.000+05:30

This simple power supply circuit provides 12V regulated voltage with 3A constant current. It is specially
designed for use with 2m handheld rigs with linear power amplifier and CB portable QRP rigs.

Circuit diagram of Power Supply Using CA3085 : Click on image to enlarge

The circuit uses monolithic IC CA3085 voltage regulator in 8-lead TO-5 package. Its salient features include good load and line regulation, output current up to 100mA (which can be increased to several amperes with additional pass transistors), output short-circuit protection, and lower input voltage.

A low power dissipation is achieved by driving external series-pass transistor 2N4241 (T1) from pin 2 of CA3085. Normal output pin 8 is returned to ground via diodes D3 and D4 to ensure error amplification operation in the linear region. Ripple rejection is approximately 50 dB on no load and 35 dB on full load. A 2x2x2.5cm aluminium heat sink fastened onto a 1.5mm blackened aluminum sheet of 12.5cm2 area on 2N4241 helps the circuit in dissipating heat without exceeding maximum device ratings.

CA3085 can dissipate up to 650mW power in free air, without any heat sink. AFCO-make C-05-4 heat sink is suitable for this IC. An improper heat sink may cause device junction temperature to exceed the limit, resulting in progressive deterioration of the device.