About electronics

Where To Buy Electronic Components And Parts!

2011-12-14T03:28:00.001-08:00

ELECTRONIC COMPONENTS

USA (global) suppliers:

All Electronics
Allied Electronics
Alltronics
BG Micro
Circuit Specialists
Digikey
Dipmicro
Electronic Goldmine
Element14
Halted
J-Tron
Jameco
Mouser
Newark (Element14)
OnlineComponents
Tayda Electronics
West Florida ComponentsUK suppliers
Farnell Electronics (Element14)
Maplin Electronics
Rapid Online

RS Online Australian suppliers:

Jaycar New Zealand suppliers:

Jaycar Belgium suppliers:

Conrad HARDWARE, MATERIALS AND PARTS---------------------------------------------------------USA (global) suppliers:

Grainger

Jameco
MasterBond (Adhesives)

McMaster-Carr (US Only)
Proto Stack

Small PartsAustralian suppliers:
Small Parts

Where To Buy Electronic Components And Parts

2011-12-14T03:17:00.001-08:00

ELECTRONIC COMPONENTS

2011-12-14T03:15:00.000-08:00

ELECTRONIC COMPONENTS
click the following link

Allied Electronics

Where To Buy Electronic Components And Parts

2011-12-14T03:04:00.000-08:00

Where To Buy Electronic Components And Parts

click th link here All Electronics

What is R&D focus?

2011-12-14T02:59:00.000-08:00

The Matrix R&D is focused on strengthening the existing
product portfolio. We are developing new products which
can cater to varied applications to meet customers’ specific
needs. Currently, we are working on converged solution in
telecom. Besides this we are working on next-generation
user terminals and enterprise gateway devices to strengthen
our existing telecom product line.
On the security side, we are developing video surveillance
systems after the launch of access control, time attendance
and fire-alarm systems in quick succession.

VERY IMPORTANT BASIC ELECTRONICS

2011-07-26T05:06:00.000-07:00

Basic concepts
If you have ever looked at a battery, you will find that there are usually two metal contacts. One is called the positive (+) side, and the other is called the negative side (-). If you connect a wire directly between these two poles, an electrical current will flow through the wire. An electrical current is made of electrons that flow through the wire much in the same way that water would flow through a hose. If I replace the wire with a bunch of electronic components, the current still flows, and it causes something useful to happen. For example, if I connect the two wires of a radio to the battery, I might hear the a baseball game. Most of electronics is the study of how we can connect things to a battery to make that current do something useful. As long as you keep the idea that all electronic circuits affect how the current gets from one side of the battery to the other, you will be able to figure out most electronic circuits.
Whats a circuit? A circuit is the path by which the electricity flows from one end of the battery to the other. A circuit could be as simple as a single length of wire, or as complicated as a mainframe computer. The principles, however, are always as simple as giving that current somewhere to go.
Circuits are usually described by pictures, called a schematic drawing, or schematic for short. It is usually the easiest way to describe the circuit, and to insure that someone else can interpret what the circuit is going to do. The following schematic shows some really common symbols that you might see in your work with robotics.

Battery
There are many types of batteries, but they typically share the same schematic picture. The drawing has two ends to it. Notice that top has a long thin line. The bottom has a short fat line. The long thin line is the positive (+) terminal for the battery. The short fat line is the negative (-). The long bar is usually drawn at the top of the battery, but be careful because not everyone follows this practice.
Resistor
A resistor is a device that doesn't allow current to flow as well as a normal length of wire. It resists the flow of current, hence the name. Resistence is measured in Ohms. The higher the Ohm value, the more it resists the flow of current. Resistors come in values from .1 ohm to 10 megaohms (ten million ohms). Common values used in robotics are 10k (10,000 ohms), 4.7k (4700 ohms), and 330 ohms. Note the use of K (kilo or 1000) as a short hand. If you see 10k on a schematic, it means 10 * 1000. The other major abbreviation is M (mega or 1,000,000).
Switch
A switch is a device that allows you to stop the flow of current entirely. These are usually mechanical devices that seperate two bits of metal. When the metal doesn't touch, current doesn't flow. When the metal touches, is called a closed circuit. When the metal doesn't touch, is called an open circuit. (closed = ON, open = OFF)
Diode
A diode is an interesting device. It is a semi-conductor. The Diode is the most basic of semiconductors. Is function is to allow electricity to flow in one direction, but not the other. It is like a one way valve for electricity. By looking at the schematic symbol, you can see that has the shape of an arrow. The electrical current will flow in the same direction as the arrow. Thats how you know which way the diode is oriented in the schematic. There are special terms used for each side of the diode. The positive side of the diode is called the ANODE. The negative side is called the CATHODE. Current always flows from the ANODE to the CATHODE.
LED
LED stands for Light Emitting Diode. An LED is a diode with a unique property that when electricity flows through it, it emits light. These are extremely useful, require very little power to operate, and you will find them to be very useful. The ANODE and CATHODE are the same as on a regular diode. The way you know that it is an LED is by the little arrows pointing away from it. That is supposed to represent light energy being transmitted.
There are hundreds of other parts you might see in electronic schematics, but these 5 are a good start for now. I will show some more parts later. Lets use these parts in the following schematic, and I will describe what we are looking at.
As you can see in the schematic drawing, there are schematic symbols for each part, and each is labeled with a name, and a value where appropriate. For example, the battery has a value of 6 volts, and the resistor has a value of 330 ohms. Even the LED labeled L1 has a value, which is RED.
The lines in the picture above are supposed to represent wires. Therefore, you will connect a wire between the batteries positive terminal and one terminal on the switch. Then connect the other terminal on the switch to one end of the resistor. The other end of the resistor to the anode of the diode, and the cathode of the diode to the negative terminal of the battery.
So, you might ask, what does the above circuit do? Lets do a quick analysis. If it is built and wired correctly, closing the switch SW1 will allow current to start to flow. The current will flow through resistor R1, which will prevent too much current from flowing. More on that later. The current will then flow across the Light Emitting Diode, L1, causing it to emit light. Opening in the switch will do the opposite by causing the current to stop.
Volts, Current, and Resistance
These are a few interesting concepts that are really easy to learn. Electricity flows a lot like water flows. Lets assume there is a tank of water sitting on a table. And, there is a hose connected to the bottom of the tank. This is just like a battery and a wire. The battery is full of electrons, and the wire is a place for the electrons to flow.
The water in the tank will generate some pressure in the hose. How much pressure depends on the size of the tank. Water pressure is measured in pounds per square inch (PSI). Electricity works in a very similar way. A battery generates 'electrical pressure', and is measured in a unit called a Volt.
If the end of the hose allows water to flow out of it, then there is flow through the hose. Lets assume it is flowing out onto the ground, which is where the water wants to go because of gravity. This is usually measured in gallons per minute. In electricity, if a wire is connected between the positive and negative terminals of the battery, then electrons start to flow. This is called Current, and is measured in Amperes, or Amps.
With the water, the amount of water that can flow depends on the size of the hose. A very small hose provides a very small path for the water. The smaller the hose, the smaller the water flow. Electricity has a similar thing, called resistance. Almost all electrical conductors have some amount of resistance to them, even plain wire. The lower the resistance, the more electrical current flows.
In moving water around, it turns out that water pressure and pipe diameter determine how much water can flow through the pipe. If you raise the water pressure in a fixed size pipe, then more water flows through it (at a faster rate!). You could also leave the water pressure alone and put in a bigger pipe. This would have the same affect.
In electricity, a similar relationship exists. The amount of current depends on the resistance and the voltage (i.e. pipe size and pressure). There is a little formula for calculating this. Its called Ohms law, and it says that Voltage = Current * Resistance. Using algebra, you can determine any one of these values by solving for it. So, Current = Voltage / Resistance, Resistance = Voltage / Current.
The important point is that these three values are related. Changing one of the values is going to affect the other two.
Now that I have told you this, let me explain why. It turns out that normal wire has very low resistance. Often, its in the neighborhood of .01 ohms, or even less. If you use a 6 volt battery, and connect a plain wire across its terminals, then the amount of theoretical current flow is Current = Voltage / Resistance, or Current = 6 / .01 which equals 600 amps. Now, it turns out that most batteries will only hold around 2 or 3 amps. This means the battery will drain almost immediately, which is not good. To use the water analogy, a very low resistance wire is like a really big pipe. In fact, in this case, the pipe is almost the same diameter as the tank. If you allow the water to flow, it will empty the tank all at once.
There is some additional danger involve here. It turns out that when electrons flow through a wire, they encounter some friction as they pass through the wire. Normally, this isn't a problem. However, if too many electrons flow through a wire, then the wire will become very very hot, and could melt. You have seen this if you have ever looked at a normal light bulb. The way an light bulb works is by allowing a lot of current to flow through a very small wire. The wire turns white hot and would like to burn away. However, since light bulbs have no air in them, the wire cannot burn, so it is stuck being very very hot.
So, as a rule, you should never allow electricity to flow from one end of the battery to the other without using some sort of resistance. If this occurs, its called a short circuit, and will usually start to burn or at least smoke badly. Perhaps you have heard the term electrical short or shorted out when referring to a badly damaged electronic gadget. It isn't a good situation.
Now, armed with that information, lets look at our first circuit again, this time looking at resistance.
Circuit #1
When the switch is closed, current starts to flow. The switch itself has very little resistance, so we won't count it. The current then flows through the resistor. The resistor will limit the amount of current that flows in this circuit. It turns out that the amount of current that flows through this circuit is determined by the total resistance of the circuit. In this example, only one device has resistance, therefore the total resistance is 330 ohms. The current then flows through the LED, which doesn't have resistance, and then to the negative terminal of the battery. Using Ohms law, I can tell you that the amount of current flowing is
Current = 6 volts / 330 ohms
Current = .018 amps
This means the amount of current flowing through the circuit is .018 amps, or 18 MilliAmperes, which is abbreviated 18mA (milli, or lowercase 'm' means divided by 1000, and is commonly used to talk about amperage. 1 Amp, or 1000 mA, turns out to be a rather large amount of power.)
This resistance is extremely important in our circuit. First, it insures that we haven't created an electrical short. Second, it turns out that the LED has some really small wires inside it, and cannot be allowed to carry very much current. In fact, most LED's will burn up if you allow more than 30mA to pass through them. In this case, our resistor is filling the role of a 'current limiting resistor', which you will see alot in robotics and digital electronics. In most circuits that have a resistor connected in series with another part, the resistor is there to limit the amount of current that flows.
For series resistors (thats a resistor connected to another resistor, such as shown below), you add the two values to determine the total resistance.
Circuit #2
For example, in circuit #2, I added an additional resistor. This means the resistance is added, so we now have 660 ohms resistance.
Current = 6 volts / 660 ohms
Current = .009 amps
Now the circuit only has 9 mA of current. This means that the LED will not shine as brightly. However, the circuit also doesn't drain the battery as fast. In theory, the battery should now last twice as long.
In Summary
Voltage Current and Resistance are all inter-related in an electrical circuit. If you know two of them, you can solve for the third.
Resistors are important components that limit the current flow
Never short out a battery or a circuit. There MUST always be a resistance in a circuit
LED's require a current limiting resistor.
Switches do not have resistance.
Resistance in series can be added together.
Pop Quiz #1
Using what you learned above, take a quick second to see if you can figure these little problems out.
1. How much current is going to flow through this circuit?
2. The LED in the circuit, L3, can only handle 25mA of current. What value should the limiting resistor R4 be to keep L3 from burning up?
3. The following circuit has two resistors and an LED. How much current will flow through the LED L4? (Hint: Even with the LED4 in the middle, these two resistors are in series)
4. If the LED L4 can handle up to 25mA, will it be safe in this circuit?
Here are the answers to check your work.
Answers to Pop Quiz 1
All of these questions need Ohms Law for the answer. Remember,
Voltage = Current* Resistance
Current = Voltage / Resistance
Resistance = Voltage / Current
Question 1:
Resistance = 270, Voltage = 10, therefore
Current = Voltage / Resistance
Current = 10 volts / 270 ohms
Current = .037 or 37mA
Question 2:
Here, we know that the Current is going to be 25mA, or .025, and the Voltage = 10. So, we need to solve for the Resistance.
Resistance = Voltage / Current
Resistance = 10 volts / .025 A
Reistance = 400 ohms
This means the circuit should use a 400 ohm resistor to insure that the LED does not burn up.
Question 3:
Series resistors are added together to form the total resistance for the circuit.
Current = Voltage / Resistance
Current = 6 volts / ( 270 ohms + 100 ohms)
Current = 6 volts / 370 ohms
Current = .016 or 16mA
Question 4:
16mA is less than 25mA. The LED will only burn up if we exceed 25mA, which we haven't. Therefore, it is a safe resistance.

Intel 8255

2010-12-18T02:23:00.000-08:00

Pinout of i8255

The Intel 8255 (or i8255) Programmable Peripheral Interface chip is a peripheral chip originally developed for the Intel 8085 microprocessor, and as such is a member of a large array of such chips, known as the MCS-85 Family. This chip was later also used with the Intel 8086 and its descendants. It was later made (cloned) by many other manufacturers. Are in DIP 40 and PLCC 44 pins encapsulated versions

This chip is used to give the CPU access to programmable parallel I/O, and is similar to other such chips like the Motorola 6520 PIA (Peripheral Interface Adapter) the MOS Technology 6522 (Versatile Interface adapter) and the MOS Technology CIA (Complex interface Adapter]] all developed for the 6502 family. Other such chips are the 2655 Programmable Peripheral Interface from the Signetics 2650 family of microprocessors, the 6820 PIO (Peripheral I/O) from the Motorola 6800 family, the Western Design Center WDC 65C21, an enhanced 6520, and many others.

The 8255 are used in home computers as SV-328 and all MSX, but is perhaps most well known for its use in the original IBM-PC's parallel printer port (now largely defunct and replaced by the USB standard, and considered a legacy port).

However, most often the functionality the 8255 offered is now not implemented with the 8255 chip itself anymore, but is embedded in a larger VLSI chip as a sub function. The 8255 chip itself is still made, and is sometimes used together with a micro controller to expand its I/O capabilities.

Artificial intelligence

2010-01-16T06:44:00.001-08:00

Artificial intelligence
* Aircrafts and parts
* Advanced materials, composites and specialty metals
* Computers, electronic components, and systems
* Fighters and attack aircraft
* Government defense policies and goals
* Lasers
* Navigation controls and guidance systems
* Ordinance and Military vehicles
* Computers, electronic components, and systems
* Aviation electronic/Avionics
* Robotics
* Satellites
* Search and detection equipments
* Strategic defensive initiative
* Sensors and instrumentation
* Ships
* Space vehicles and commercialization of space

Constructional Phone Projects

2009-08-09T16:09:00.002-07:00

Introduction

A phone basically consists of a switch, a speaker and a microphone. A hook switch is used to connect and disconnect it from the network. It connects when you lift the handset. A speaker is generally a 8-ohm speaker. A microphone

in the past is as simple as carbon granules compressed between two thin metal plates. Sound waves from your voice compress and decompress the granules, changing the resistance of the granules and modulating the current flowing through it.

There are many projects that one can experiment with it. However, please check with the regulatory body of your country to ensure that what you are doing is legal and allowed by the regulator.

Constructional Project

The constructional projects are listed below.

Telephone Recorder Project
This recorder project will enable you to record both sides of your conversations. Once constructed, this switch will allow you to automatically turn on your tape recorder when you pick up the handset.

Telephone Hold Project for 2 phones in parallel
This telephone hold project will enable you to hang up one telephone without losing connection and move to another room and pick up a different telephone.

Telephone Line In Use Indicator Project
This project will have an LED indicator to indicate whether the telephone line is in use or otherwise.

Another Simple telephone In Use Indicator Project
This is another variation of telephone in use indicator project that uses 13 parts to build. Yellow LED ON indicates line in use and green LED ON indicates that line is not in use.

Constructional Motor Control Projects

2009-08-09T16:09:00.001-07:00

Introduction To Motor Control

There are many types of motors that are in used these days. The common ones are DC types, AC types, stepper motors and brushless DC motors.

In the electronics hobbyiest projects, most designer will likely to encounter the use of stepper motor as this is the most widely used in many applications. There are basically 2 types of stepper motor namely unipolar type and bipolar type.

Bipolar motors have two coils and are controlled by changing the direction of the current flow through the coils in the proper sequence. These motors have only four wires.

Unipolar motors have two center-tapped coils which are treated as four coils. These motors can have five, six or eight wires. Unipolar motors may be connect as bipolar ones by not using the ‘+’ wires.

There are also servo motors which are frequently used in remote control aeroplanes, remote control toys and in automation processes. They are controlled using pulse coded modulation.

Monostable Operation

2009-08-09T16:08:00.000-07:00

Monostable Operation

Figure below shows the monostable operation of a 555 IC.

In this mode, the device generates a fixed pulse whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to pin 2 falls below Vcc/3 while the its output is low, its internal flip-flop turns the discharging transistor Tr off and causes the output to become high by charging the external capacitor C1 and setting the flip-flop output at the same instant.

The voltage across the external capacitor C1, VC1 increases exponentially with the time constant T=RA*C1 and reaches 2Vcc/3 at td=1.1RA*C1. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RA*C1, the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant RA*C1 controls the output pulse width. When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the discharging transistor Tr on. At this time, C1 begins to discharge and its output goes to low.

Astable Operation

An astable operation is achieved by configuring the circuit as shown above. In the astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multivibrator. When its output is high, its internal discharging transistor Tr turns off and the VC1 increases by exponential function with the time constant (RA+RB)*C.

When the VC1, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high, resetting the F/F and causing its output to become low. This in turn turns on the discharging transistor Tr and the C1 discharges through the discharging channel formed by RB and the discharging transistor Tr. When the VC1 falls below Vcc/3, the comparator output on the trigger terminal becomes high and the timer output becomes high again. The discharging transistor Tr turns off and the VC1 rises again. The frequency of oscillation is given as below.

Constructional Timer Projects

2009-08-09T16:07:00.002-07:00

Introduction

Timer circuit has been used in many projects and there are basically 2 types that are used these days. One of them is the use of analog RC circuit where charging of the capacitor circuit determined the T(time) of the circuitry. This type of circuitry has larger tolerance and is used in applications where the T is not so critical as the T is affected by the tolerance of the RC components used.

The other is the use of crystal or ceramic resonators together with microprocessor, microcontroller or application specific integrated circuit that need higher precision T in the tolerance of up to 5 ppm (parts per million).

555 IC

One commonly used circuit is the 555 IC which is a highly stable controller capable of producing timing pulses. With a monostable operation, the T(time) delay is controlled by one external resistor and one capacitor. With an astable operation, the frequency and duty cycle are accurately controlled by two external resistors and one capacitor. The application of this integrated circuit is in the areas of PRECISION TIMING, PULSE GENERATION, TIMING DELAY GENERATION and SEQUENTIAL TIMING.

A typical 555 IC block diagram is as shown below.

Anti-Pinch Window Lift Automotive Electronics Project

2009-08-09T16:07:00.001-07:00

Automotive Electronics

In automotive electronics networking, the commonly networking standard used is called CAN or controller area network which uses a baud rate of up to 1Mbps. This speed is needed in the control of engine and other critical components of the automobile that requires fast transfer of information. However, there are some areas of control which does not require that kind of speed and hence a slower speed standard can be utilised to save control cost. Some of these areas are the mirrors control, Window lift, seat control and door lock amongst others.

Due to this requirements, a consortium was formed in 1998 consisting of 5 automotive manufacturers (Volvo, BMW, Audi, VW and Daimler-Chrysler), 1 tool supplier (VCT) and 1 semiconductor supplier (Motorola) to look into this. As a result, the LIN (Local Interconnect Network) specifications was finalised on 2 February 2000. The first version of LIN was 1.1 and currently version 2.0 is in use. The most recent development in LIN is the use of it over the vehicle's battery line using a DC-LIN transceiver. Some of the main features of LIN are listed below.

One master and up to 16 slaves. No collision detection feature is needed as master initiated all messages communication with slaves. The master is usually implemented with a more powerful microcontroller compared to the slaves as it has to handle more tasks.
Baudrate of up to 20kbps. Slower speed is chosen to reduce the effect of electromagnetic interference.
Single wire implementation based on enhanced ISO 9141.
Simple SCI or UART hardware interface which is available in most microcontroller chips making its implementation cost effective.
Self synchronization in the slave nodes without the need to have crystal or ceramic resonator. Internal RC oscillator for the microcontroller is good enough and hence making its implementation lower cost.

Constructional Amplifier Projects

2009-08-09T16:06:00.001-07:00

Introduction to Amplifier

Amplification is the process of increasing the amplitude of a AC signal current or voltage such as audio signal for sound or video signal for a television picture. The amplifier allows a small input signal to control a larger amount of power in the output circuit. The output signal is a copy of the original input signal but has higher amplitude.

Amplification is neccessary as in most applications, the signal is too weak to be used directly. For example, an audio output of 1mV from a microphone is not able to drive a loud speaker which requires a few volts to operate. Hence, the signal need to be amplified to a few volts before it can be fed into the loud speaker.

NPN Transistor Circuit Configurations

An example of different type of transistor configurations in the circuit is as shown in Figure 1 below.

a) The common emitter(CE) circuit uses emitter as its common electrode. The input signal is applied to the base and the amplified output is taken from the collector. This is the one generally use because it has the best combination of current gain and voltage gain.

b) The common base (CB) circuit uses base as its common electrode. The input signal is applied to the emitter and the amplified output is taken from the collector. The relatively high emitter current compared to the base current results in very low input impedance value. For this reason, the CB circuit is seldom used.

c) The common collector (CC) circuit uses collector as its common electrode. The input signal is applied to the base and the amplified output is taken from the emitter. This circuit is also called an emitter follower. This name means that the output signal voltage at the emitter follows the input signal at the base with the same phase but less amplitude. The voltage gain is less than 1 and is usually used for impedance matching. It has high input at the base as a load for the preceding circuit and low output impedance at the emitter as a signal source for the next circuit.

Classes

They can be classified into classes A, B, C and AB. They are defined based on the percent of the cycle of input signal that is able to produce output current.

In Class A, the output current flows for the full cycle of 360 degree of input signal. The distortion is the lowest with around 5% to 10% and an efficiency of 20% to 40%. In general, most small signal operate class A

In Class C, the output current flows for less than one half of the input cycle. Typical operation is 120 degree of input current during the positive half cycle of the input current. This class has an efficiency of 80% but has the highest distorton. This class is usually used for RF amplificaton with a tuned circuit in the output.

In Class B, the output current flows for one half of the input cycle which is around 180 degree. Class B operaton lies between class A and class C. Clas B are usually connected in pairs and in such a circuit called push-pull amplifier. The push-pull is often used for audio power output to a loud speaker.

In Class AB, it offers a compromise between the low distortion of class A and the higher power of class B. It is usually used for push-pull audio power amplifiers.

Security and Surveillance DIY Projects

2009-08-09T16:05:00.001-07:00

The following security and surveillance projects will help one to understand the basics of how home security and surveillane projects work. It will have topics like constructing a siren that emits audible sound once intruder comes near, alarm, 2 way intercoms system, light alarm and other surveillance projects which will be added from time to time.

Constructing your own FM/Ultrasonic/Infra Red Wireless Projects

2009-08-09T16:03:00.001-07:00

Ever since I was a student years ago, I was always fascinated by the world of wireless and wondered how they worked. The projects below will provide a good understanding and information of the world of remote controls. The projects includes schematic diagrams and parts list to enable one to construct and experiment with the concept of infrared, ultrasonic and FM transmitters.

Constructing your own FM/Ultrasonic/Infra Red Wireless Projects

2009-08-09T16:03:00.000-07:00

Electronics Hobbies Projects Schematics and Parts List References

2009-08-09T16:01:00.002-07:00

The following list below describes the projects that electronics hobbies enthusiasts can put their knowledge of electronics into practical experience by getting the materials themselves and build the projects or simply by getting some closely related projects from off the shelves products.

These projects will be useful for high school students, teachers, colleges and university students, electronics hobbyist and electronics designers. All one needs to know is basic electronics, some know-how of soldering, component identification and the determination to learn.

The following are some of the constructional projects that one can embark on :

Digital Dice Project
This Digital Dice electronic project uses a combination of 555 timer, 7490 decade counter, 7483 4-bit binary adder, 7447 BCD to 7 Segment Decoder in dispaying a random number on the seven segment display once a button is pressed and released.

120 Seconds Message Recorder Project
Record and playback messages up to 120 seconds using Winbond ISD25120 Integrated Circuit.

Alarm and Music Generator Project Using UM66TXXL
This simple electronics circuit utilizes a UM66TXXL TO92 package CMOS IC that generates song depending on the type of IC used.

Melody Music Generation Project
This project based on the M348X IC and is the electronic equivalent of a mechanical music box.

Audio Signal Tracer Circuit
This electronic project schematics function is to enable one to trace an audio signal through a maze of wires running around the house.

Variable Frequency Audio Oscillator Using MC34119 IC
This basic electronic project can be used as a low level alarm generator or a code practice oscillator. It is centred around MC34119 IC which is a low power audio amplifier.

Electronics Hobbies Four Level Voltage Detector Project
This simple circuit using LM339 Comparator can be applied as a bargraph voltmeter.

3 1/2 Digit LED Panel Meter Project
Construct a general purpose 3 1/2 Digit LED Panel Meter Using Intersil 7107 IC with LED Drivers that can be used to measure voltages, currents, and other customized applications.

3 Digit Counter Electronic Project Schematic
Construct a 3 digit counter for general applications using Binary Coded Decimal counter.

Touch Switch And Delay Circuit Project
Construct a touch switch 4 seconds delay circuit using 555 timer IC.

Touch Switch/Contact Switch Circuit
Construct a touch/contact switch using 4011 NAND Gates IC to turn ON and OFF a relay.

Touch Switch Using 4001 IC
Construct a touch/contact switch using 4001 NOR Gates IC to turn ON and OFF a LED.

TTL/CMOS Logic Probe
Construct a TTL/CMOS Logic Probe that is able to examine the logic states at a particular point in an electronic circuit. Schematic and parts list are provided.

Battery Tester Project
Build this dry cell or rechargable battery tester project that is able to determine the charge of the battery. The knowledge of using LM3914 is attained by building this project.

Color Sensor
This electronics hobbies color sensor project from Electronics Zone website is able to sense the color of objects that are placed in front of the convex lenses which in turn feed the light to the light dependent resistor or LDR.

Engineering Free Magazine

2009-08-09T16:01:00.001-07:00

The following are some engineering free magazine available to cater for your various engineering needs :

EE Times
EE Times provides direct access to 150,000 high-level professionals involved in design/development engineering and management. EE Times is consistently chosen as the best-read and most preferred publication in the industry.

EE Times delivers business and technology news every week to engineers and technical managers in the electronics industry. Besides reporting the news, editors analyze key industry trends and developments, put the news into perspective and predict what is likely to happen next. Opinion from leaders of government and industry is also part of the editorial fiber of the paper.

Electronic Design
Electronic Design's on-going objective is to observe and report the latest breakthroughs in EOEM technology. By providing this information Electronic Design has been the strategic partner of system designers and suppliers for the past 50 years, helping to bring them together so that they can deliver more competitive products to market faster.

Embedded System
Embedded Systems Design is a magazine for engineers, programmers and electronics hobbyists who are into using microcontroller and embedded microprocessor-based systems in their design.

This magazine provides best practices and peer guidance for Senior Systems Designers and their teams. These are the key designers responsible for defining systems, selecting the critical hardware and software components, building the systems, and integrating the hardware and firmware designs. This systems design magazine highlights the significant design methodologies, strategies and new products engineers need to gain a competitive advantage.

Electronic Products
Electronic Products reports on important developments in products and product technology. Its editorial serves as a key information source for engineers and managers.

Electronic Products focuses on the new product and product technology needs of engineers designing today's electronic equipment and systems. From cover to cover, month after month, we provide the relevant, timely product and product technology information today's engineers need to make informed buying decisions.

Test and Measurement
Test & Measurement World is the leading publication for engineers involved in electronics test, measurement, and inspection.

Test & Measurement World provides practical content and industry updates for engineers and engineering managers who are involved in using and buying equipment, software and services for test, measurement, inspection, and quality control during development, design and manufacturing or field service. 11 issues per year.pr

Electronics Project and Design Blog

2009-08-09T15:57:00.000-07:00

Welcome to my blog on electronics project and design. It will give you the latest updates on electronics projects, latest update on electronics components and also inform you of any new pages added into this website.

To subscribe (no e-mail necessary), all you have to do is right-click on the orange RSS button (see buttons to the left), copy shortcut and then paste the URL into your RSS reader. Alternatively, you can just click on the My Yahoo! button or My MSN or Add To Google button if you keep a personalized home page there.

CDR Sam Where Optical Storage Looks to the Future of Recordable Blu-ray Discs and Beyond

2009-08-09T15:51:00.000-07:00

I have to say after several years of using a DLT drive from a very well known American computer manufacturer and having to replace it every year that I wonder about our technology. I see the same Tech every year and we discuss the state of equipment and look at the IBM eServers that are over ten years old and an old IBM DLT tape autoloader that has been running for 10 years. It runs on SCSI and I’ve not been in a terrible hurry to put in an old SCSI (I’m not sure it would even fit with the PCIexpress slot).

This has got me thinking about flash drive backup. Essentially running a PC connected USB Flash duplicator as a port for data sets of drives.

So here is how it works.

You connect the flash drive back up unit via USB to the server.

Each drive is labeled or has a key label attached on the lanyard. Drives can be stored in a key rack.
Each drive is the back-up media. Each day is written to one flash drive and then the next day is written to a new drive. Past days can be removed and stored off site.
Flash drives have no mechanical parts that fail. No tape that jams, no drive heads that wear out.
The system could have a lockable cover to protect the drives from ‘accidental’ removal
Each drive would need to be recognized by the back up software as a back up media
Cycle the drives out like we cycle out tapes. Retire them after 2 years.

You can tell I’ve had it with DLT. The drives are not cheap by any standard nor are the tapes. Stay tuned.

download Microsoft Robotics Developer Studio 2008 R2 x86 | 419 MB

2009-08-09T15:50:00.002-07:00

Microsoft Robotics Developer Studio 2008 R2 x86 | 419 MB

Microsoft® Robotics Developer Studio 2008 R2 Express Edition enables hobbyists and non-professional developers to create robotics applications targeting a wide range of scenarios.

Microsoft Robotics Developer Studio supports a broad set of robotics platforms by either running directly on the platform or controlling it from a Windows device through a communication channel such as Wi-Fi or Bluetooth®.

In addition to providing support for Microsoft Visual Studio, Microsoft Robotics Developer Studio 2008 R2 Express Edition provides a visual programming environment which allows developers to create applications simply by dragging and dropping components onto a canvas and wiring them together.

The powerful Visual Simulation Environment provides a high-fidelity simulation environment powered by NVIDIA™ PhysX™ engine for running game-quality 3D simulations with real-world physics interactions.

To help developers getting started, the studio contains extensive documentation and a large set of samples and tutorials that illustrate how to write applications ranging from simple "Hello Robot" to complex applications that simultaneously run on multiple robots.

System Requirements

* Supported Operating Systems: Windows Vista; Windows XP

In addition to using Microsoft Robotics Developer Studio 2008 R2 Express Edition as a stand-alone development environment, it can be used with any of the Visual Studio 2008 Express Editions, Visual Studio 2008 Standard Edition, Visual Studio 2008 Professional Edition or Visual Studio 2008 Team System Edition.

Instructions

Important: Make sure you have the latest service pack and critical updates for the version of Windows that you are running. To find recent security updates, visit Windows Update.

1. Click the Download button on this page to start the download
2. Do one of the following:
* To start the installation immediately, click Run.
* To save the download to your computer for installation at a later time, click Save.
* To cancel the installation, click Cancel.

http://www.filefactory.com/file/ag8d0d1/n/Microsoft_Robotics_Developer_Studio_2008_R2_Standard_x86-CRBS_part1_rar
http://www.filefactory.com/file/ag8d0dg/n/Microsoft_Robotics_Developer_Studio_2008_R2_Standard_x86-CRBS_part2_rar
http://www.filefactory.com/file/ag8d0ef/n/Microsoft_Robotics_Developer_Studio_2008_R2_Standard_x86-CRBS_part3_rar
http://www.filefactory.com/file/ag8d0d9/n/Microsoft_Robotics_Developer_Studio_2008_R2_Standard_x86-CRBS_part4_rar
http://www.filefactory.com/file/ag8d0e1/n/Microsoft_Robotics_Developer_Studio_2008_R2_Standard_x86-CRBS_part5_rar

http://ul.to/1gj5bu
http://ul.to/2oegiu
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http://ul.to/6bh7i4

http://rapidshare.com/files/247244387/Microsoft.Robotics.Developer.Studio.2008.R2.Standard.x86-CRBS.part1.rar
http://rapidshare.com/files/247244141/Microsoft.Robotics.Developer.Studio.2008.R2.Standard.x86-CRBS.part2.rar
http://rapidshare.com/files/247244124/Microsoft.Robotics.Developer.Studio.2008.R2.Standard.x86-CRBS.part3.rar
http://rapidshare.com/files/247244198/Microsoft.Robotics.Developer.Studio.2008.R2.Standard.x86-CRBS.part4.rar
http://rapidshare.com/files/247243939/Microsoft.Robotics.Developer.Studio.2008.R2.Standard.x86-CRBS.part5.rar

download Synaptris IntelliVIEW Designer v4.1.0.24 | 34.1 MB

2009-08-09T15:50:00.001-07:00

Synaptris IntelliVIEW Designer v4.1.0.24 | 34.1 MB

Decisions that are made on a daily basis are key to the success of a business. From materials management and production planning to sales and cash flow management, everyone in the enterprise needs reliable information to make the right decisions based on the business situation at hand. With business situations becoming increasingly dynamic, information and data presentation needs are also becoming more diverse. As a result, intelligent organizations are constantly striving to enable every stakeholder gain greater business insights to eliminate inefficiencies, exploit untapped potential and make better decisions.

http://www.easy-share.com/1905544688/Synaptris.IntelliVIEW.Designer.v4.1.0.24.WinALL.Incl.Keygen-BRD.rar

http://rapidshare.com/files/240976159/Synaptris.IntelliVIEW.Designer.v4.1.0.24.WinALL.Incl.Keygen-BRD.rar

http://hotfile.com/dl/5147778/df19a61/Synaptris.IntelliVIEW.Designer.v4.1.0.24.WinALL.Incl.Keygen-BRD.rar.html

WaveMetrics IGOR Pro 6.0.5 | 88.18 Mb

2009-08-09T15:49:00.000-07:00

WaveMetrics IGOR Pro 6.0.5 | 88.18 Mb

IGOR Pro is an interactive software environment for experimentation with scientific and engineering data and for the production of publication-quality graphs and page layouts. IGOR has been used by tens of thousands of technical professionals since its introduction in 1989. It combines power with ease of use by providing a programming environment for the sophisticated user along with the ease of point and click for the beginner and expert alike.

Letitbit

Uploading

FileFactory

Maple R13, The Essential Tool for Mathematics Modeling | 270 MB

2009-08-09T15:48:00.002-07:00

Redefining Usability
Maple’s Smart Document Environment is an intuitive user-interface that automatically captures all of your technical knowledge. It has many built-in tools to assist you in analysis and solution development. During this brief demonstration, you will see firsthand how Maple’s easy-to-use equation editor, context menus, palettes, and other interactive features allow you to start creating solutions – fast.

http://rapidshare.com/files/232704445/Maplesoft.Maple.v13.0-TBE.part1.rar
http://rapidshare.com/files/232708939/Maplesoft.Maple.v13.0-TBE.part2.rar
http://rapidshare.com/files/232712153/Maplesoft.Maple.v13.0-TBE.part3.rar
or
http://www.megaupload.com/?d=R72P7Z3J
http://www.megaupload.com/?d=1UDXB6TA
http://www.megaupload.com/?d=TXBB92ZM

OriginLab OriginPro 8.0 SR5 | 162 MB

2009-08-09T15:48:00.001-07:00

OriginLab OriginPro 8.0 SR5 | 162 MB
OriginLab produces professional data analysis and graphing software for scientists and engineers. Our products are designed to be easy-to-use, yet have the power and versatility to provide for the most demanding user.

OriginPro 8 offers all of the features of Origin plus extended analysis tools for statistics, 3D fitting, image processing and signal processing.

Rapidshare

Mirror link

http://hotfile.com/dl/2417803/f77e492/odlbixnd.zip.html

COMSOL Multiphysics v3.5a Multilanguage

2009-08-09T15:46:00.000-07:00

COMSOL Multiphysics v3.5a Multilanguage | 4,5 GB

“

The COMSOL Multiphysics simulation environment facilitates all steps in the modeling process —defining your geometry, specifying your physics, meshing, solving and then post-processing your results.
Model set up is quick, thanks to a number of predefined modeling interfaces for applications ranging from fluid flow and heat transfer to structural mechanics and electromagnetic analyses. Material properties, source terms and boundary conditions can all be arbitrary functions of the dependent variables.
A multiphysics simulation is achieved in minutes. Predefined multiphysics-application templates solve many common problem types. You as the user, also have the option of choosing different physics from the Multiphysics menu and defining the interdependencies yourself. Or you can specify your own Partial Differential Equations (PDEs), and couple them with other equations and physics.

Download links (Rapidshare and Hotfile)

http://hotfile.com/dl/4859627/3ed6dbb/comos.zip.html

or

http://rapidshare.com/files/240137705/comos.zip

Part 12

http://hotfile.com/dl/4924000/35374cb/COMSOL.Multiphysics.v3.5a.MULTILANGUAGE-SHooTERS-UDS.part12.rar.html

http://rapidshare.com/files/240261147/COMSOL.Multiphysics.v3.5a.MULTILANGUAGE-SHooTERS-UDS.part12.rar

FACE RECOGNITION USING ARTIFICIAL NEURAL NETWORKS

2009-07-22T04:15:00.000-07:00

FACE RECOGNITION USING ARTIFICIAL NEURAL NETWORKS

Artificial Neural Networks commonly referred to as ‘Neural Networks’ is a new branch of AI, that enabled a crude simulation of the structure of human brain electronically or in software. The inherent properties of human brain enable it to analyze complex patterns consisting of a number of elements, those individually reveal little of the total pattern, yet collectively represent easily recognizable objects. The concepts of Neural Networks have been motivated right from its inception, by the recognition that the human brain computes in an entirely different way from the conventional digital computers. The brain modeling techniques opens a new era of Computer System that learns, from experience and uses its experiential knowledge next time. This biologically inspired method is being touted as the wave of the future in computing, relieving the programmer from the cubicle of traditional algorithmic problem solving. Inherent non-linearity property of Neural Networks makes it particularly suitable in many signal-processing applications like sound, image processing etc.

Cellular Technologies and Security

2009-07-22T04:13:00.000-07:00

Cellular Technologies and Security

Electronic Program(me) Guide (EPG)

2009-07-22T04:12:00.002-07:00

Electronic Program(me) Guide (EPG)

Also known as Interactive Program(me) Guide (IPG) or Electronic Service Guide (ESG), EPG is an on-screen guide to scheduled broadcast television programs, permitting a viewer to browse, select, and discover contents based on time, title, channel, genre, etc, using their remote control, a keyboard or a phone keypad. This technology is predominant in the digital television and radio world however EPGs exist that rely upon analogue technology (using the VBI—or vertical blanking interval). EPG broadcasts data to an application residing within middleware in a set-top box which connects to the television set and enables the application to be displayed. The signals may arrive via cable TV, satellite TV, cable radio, satellite radio, or via over-the-air terrestrial broadcast stations. If the users want to see more information about the current program and future programs they have to just navigate through an EPG on a receiving device and in the same way a viewer can plan his or her viewing and also record broadcast programs to a hard disk for later viewing when EPGs are connected to PVRs, or personal video recorders.

WirelessUSB

2009-07-22T04:12:00.001-07:00

WirelessUSB

Abbreviated as "WUSB" this short-range, high-bandwidth wireless radio communication combines the speed and ease-of-use of USB 2.0 with the expediency of wireless technology and is based on the WiMedia Alliance's Ultra-WideBand (UWB) common radio platform, which is capable of sending 480 Mbit/s at distances up to 3 meters and 110 Mbit/s at up to 10 meters. However USB Implementers Forum discourages the practice of calling it WUSB and prefers to call the technology "Certified Wireless USB" to differentiate it from competitors (see below, "Competitors"). Though local regulatory policies may restrict the legal operating range for any given country, Wireless USB was designed to operate in the frequency range of 3.1 to 10.6 GHz.

Uses

WUSB are used in devices that are now connected via regular USB cables, such as game controllers, printers, scanners, digital cameras , MP3 players, hard disks and flash drives , and it is also suitable for transferring parallel video streams.

Wireless Projects

2008-12-11T10:51:00.000-08:00

Infrared Motion Detectors

2008-12-11T10:50:00.000-08:00

This Infrared Motion Detectors project is specifically designed and comes with a detailed writeup on one of the numerous applications of Infrared devices. Beginners to electronics will appreciate the construction of this project as it will teach the students of electronics how to identify resistors colour code, identification of capacitor's value, maximum working voltage and its tolerances as well as right soldering method. It includes schematic diagram, parts list, printed circuit board (PCB) pattern layout and a detailed description of each section that makes this device works.

This project describes the concept of Infrared, Operational Amplifiers concept and applications (as comparator, low pass filter, high pass filter, band pass filter etc) and sound generator integrated circuit which gives a ding-dong sound. This document also describes the troubleshooting guide and a quiz to ensure that the concept is clearly understood by the constructor.

There are many applications for the use of the detector. The most common is in the alarm system industry. Some of the new applications are automatic door openers, light switches in hallways, stairways and areas that increase safety for the public. Further applications can be seen in automatic production lines, switching of sanitary facilities, monitors and intercoms. With the ease of installation and the low suspectibility to interference from other forms of radiation, such as heaters or windows, the Infrared motion detectors are ideal devices.

You can find the AK510 Infrared Motion Detectors kit here under the SURVEILLANCE AND SECURITY (SPY) category.

How to construct your own Ultrasonic Motion Detectors

2008-12-11T10:49:00.001-08:00

This project involves constructing ultrasonic motion detectors device at 40 kHz frequency and are used to detect any moving object where this device is installed. The printed circuit board (PCB) measures only 1-1/2 by 3 inches.

The device detects motion from 4 to 7 meters away. Once that occurs, a red LED turns ON, but with additional circuitry attached to the output, the detector can turn on lights, sound buzzers, trip a recording device, or even call the police. Also, the circuit can be made to sound off with a message when anyone moves within its field of detection. Using various voice recording and playback circuits, you might even have the device provide a pleasant greeting or snarl with a barking dog sound when someone approaches the front door. As you can see, the project can be put to work in a variety of ways.

You can place it in the driveway, on the porch, garage, basement or any place where you need to be informed of any object that comes near the location.

You can find the details of the circuit diagram and PCB design for ultrasonic motion detectors here. A detailed explanation of how the circuit works is described here. First timers who construct this project will learn a great deal about ultrasonic frequency application, its concept and the difficulty encountered when installing the completed device.

Constructing an FM Phone Transmitter

2008-12-11T10:47:00.000-08:00

This project provides the schematic and the parts list needed to construct a FM Phone Transmitter

. This device attaches in series to one of your phone lines. When there is a signal on the line (that is, when you pick up the handset) the circuit will transmit the conversation a short distance. In particular it will radiate from the phone line itself. It is a passive device - there is no battery. It uses the signal on the phone line for power. No aerial is needed - it feeds back the RF signal into the phone line which radiates it in the FM band. The frequency of transmission may be adjusted by the trimcap. Note that some countries may ban any electronic device which attaches to the telephone. It is the responsibility of the constructor to check the legal requirements for the operation of this FM Phone Transmitter and to obey them.

FM Phone Transmitter Schematic

The circuit is a radio frequency (RF) oscillator that operates around 93 MHz (93 million cycles per second). Power for the circuit is derived from the full wave diode bridge. C1, C8, L3 & T1 forms the FM oscillator.

Every Tx needs an oscillator to generate the Radio Frequency (RF) carrier waves. L1, C6, T2 forms the power amplifier. Audio from the telephone lines is coupled through R3 & C2 into the base of T1 to modulate the oscillator. This is done by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. R1 & C4 act as a low pass filter.

C3 is a high frequency shunt. L2 is call a RFC (radio frequency shunt.) It decouples the power and audio from the transmitter amplifier circuit. This type of circuit usually should be calibrated. The resonant frequency of the L1-C6 amplifier circuit should be adjusted to match the resonent oscillator frequency of C1, C9-L3. However, in practice, we think you will find that the unit operates perfectly OK as it is constructed without the need to calibrate anything. If you want to try calibration you will need a frequency meter, a CRO or just trial and error.

Calibrate by moving the coils of L1 further apart. With C1 at 27p you will find that the it tunes into the FM band in the 86 - 95 MHz area. With C1 at 22p the band is raised to about 90-95mhz (depending in the coil spacing.) If you want to move this tunable area still higher to over 100MHz range then replace C1 by a 15pF or 10pF capacitor. This assumes that the on-hook voltage is about the standard 48V. If the on-hook voltage of an extension phone network is lower, say about 39V, C1 will have to be lower in the 15p to 10p range to be in the commercial FM band in this case.

Note that you should not hold the printed circuit board physically in your hands if you try to do any calibration. Your own body capicitance when you touch it is more than enough to change the oscillation frequency of the whole unit.

You can experiment the FM Phone Transmitter to get greater transmission range away from the phone line by adding an aerial (about 150 cm of 26 gauge wire) to the collector of T2.

FM Phone Transmitter Assembly Instructions

The ZTX320 has a flat and a curved side. Match these two sides with the flat and curved sides as shown on the overlay for T2. Also note these points when assembling this project:

1) Two of the three coils have enamel insulation lacquer on them. This must be physically removed from both ends of the coil before it can be soldered. Now during the manufacture of these coils they have been solder dipped to remove this lacquer. But check each leg to see that this is the case.

2) Spread out the turns in the L3 coil about 1 mm apart. The coils should not touch.

3) A solder connection (or tap) is required from the top of the first turn in the L3 coil to the pad next to the coil. Solder a piece of wire to the top of the first turn as shown on the overlay. Then solder the other end to the pad immediately next to the L3 coil.

4) The cathodes of all diodes point to the top of the PCB.

5) Attach 3" of wire with an alligator clip on the end to the pads between the diodes marked - 'TO LINE' No aerial is needed. The phone line itself acts as a sufficient aerial. To make the Kit small, resistors & diodes stand on their ends. The kit attaches to ONE of the two phone lines going to your phone. Either of the two lines will do. In most of the world this is the green or red wire. In the UK it is one of the wires attached to the terminals 2 or 5. Cut the phone line. Attach one alligator clip to one cut end and the other alligator clip to the other cut end. Take your phone off the hook and turn on an FM radio at about 93 MHz. It should be very easy to tune into the transmission. Take a portable FM receiver outside and follow the phone line.

FM Phone Transmitter Parts List

Constructing your own 3V FM Transmitter

2008-12-11T10:46:00.000-08:00

This project provides the schematic and the parts list needed to construct a 3V FM Transmitter

. This FM transmitter is about the simplest and most basic transmitter to build and have a useful transmitting range. It is surprisingly powerful despite its small component count and 3V operating voltage. It will easily penetrate over three floors of an apartment building and go over 300 meters in the open air.

It may be tuned anywhere in the FM band. Or it may be tuned outside the commercial M band for greater privacy. (Of course this means you must modify your FM radio to be able to receive the transmission or have a broad-band FM receiver.) The output power of this FM transmitter is below the legal limits of many countries (eg, USA and Australia). However, some countries may ban ALL wireless transmissions without a licence. It is the responsibility of the constructor to check the legal requirements for the operation of this kit and to obey them.

FM TRANSMITTER CIRCUIT DESCRIPTION

The circuit is basically a radio frequency (RF) oscillator that operates around 100 MHz. Audio picked up and amplified by the electret microphone is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit (the 5 turn coil and the trimcap) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. The tank circuit is connected in a Colpitts oscillator circuit.

The electret microphone: an electret is a permanently charged dielectric. It is made by heating a ceramic material, placing it in a magnetic field then allowing it to cool while still in the magnetic field. It is the electrostatic equivalent of a permanent magnet. In the electret microphone a slice of this material is used as part of the dielectric of a capacitor in which the diaphram of the microphone formsone plate. Sound pressure moves one of its plates. The movement of the plate changes the capacitance. The electret capacitor is connected to an FET amplifier. These microphones are small, have excellent sensitivity, a wide frequency response and a very low cost.

First amplification stage: this is a standard self-biasing common emitter amplifier. The 22nF capacitor isolates the microphone from the base voltage of the transistor and only allows alternating current (AC) signals to pass.

The tank (LC) circuit: every FM transmitter needs an oscillator to generate the radio Frequency (RF) carrier waves. The tank (LC) circuit, the BC547 and the feedback 5pF capacitor are the oscillator in the Cadre. An input signal is not needed to sustain the oscillation. The feedback signal makes the base-emitter current of the transistor vary at the resonant frequency. This causes the emitter-collector current to vary at the same frequency. This signal fed to the aerial and radiated as radio waves. The 27pF coupling capacitor on the aerial is to minimise the effect of the aerial capacitance on the LC circuit. The name 'tank' circuit comes from the ability of the LC circuit to store energy for oscillations. In a pure LC circuit (one with no resistance) energy cannot be lost. (In an AC network only the resistive elements will dissipate electrical energy. The purely reactive elements, the C and the L simply store energy to be returned to the system later.) Note that the tank circuit does not oscillate just by having a DC potential put across it. Positive feedback must be provided. (Look up Hartley and Colpitts oscillators in a reference book for more details.)

ASSEMBLY INSTRUCTION

Components may be added to the PCB in any order. Note that the electret microphone should be inserted with the pin connected to the metal case connected to the negative rail (that is, to the ground or zero voltage side of the circuit). The coil should be about 3mm in diameter and 5 turns. The wire is tinned copper wire, 0.61 mm in diameter. After the coil in soldered into place spread the coils apart about 0.5 to 1mm so that they are not touching. (The spacing in not critical since tuning of the Tx will be done by the trim capacitor. It is quite possible, but not as convenient, to use a fixed value capacitor in place of the trimcapacitor - say 47pF - and to vary the Tx frequency by simply adjusting the spacing of the coils. That is by varying L of the LC circuit rather than C.) Adding and removing the batteries acts as a switch.Connect a half or quarter wavelength antenna (length of wire) to the aerial point. At an FM frequency of 100 MHz these lengths are 150 cm and 75 cm respectively.

CIRCUIT CALIBRATION

Place the transmitter about 10 feet from a FM radio. Set the radio to somewhere about 89 - 90 MHz. Walk back to the FM transmitter and turn it on. Spread the winding of the coil apart by approximately 1mm from each other. No coil winding should be touching another winding. Use a small screw driver to tune the trim cap. Remove the screwdriver from the trim screw after every adjustment so the LC circuit is not affected by stray capicitance. Or use a plastic screwdriver. If you have difficulty finding the transmitting frequency then have a second person tune up and down the FM dial after every adjustment. One full turn of the trim cap will cover its full range of capacitance from 6pF to 45pF. The normal FM band tunes in over about one tenth of the full range of the tuning cap.

So it is best to adjust it in steps of 5 to 10 degrees at each turn. So tuning takes a little patience but is not difficult. The reason that there must be at least 10 ft. separation between the radio and the FM transmitter is that the FM transmitter emits harmonics; it does not only emit on one frequency but on several different frequencies close to each other. You should have little difficulty in finding the Tx frequency when you follow this procedure.

LEARNING EXPERIENCE

It should already be clear from the above circuit description that there is a surprising amount of electronics

which may be learnt from this deceptively simple kit. Here is a list of some advanced topics in electronics which can be demonstrated or have their beginnings in this project:

Class C amplifiers; FM transmission; VHF antennas; positive and negative feedback; stray capacitance; crystal-locked oscillators; signal attenuation The simple halfwave antenna used in the project is not the most efficient. Greater efficiency may be gained by connecting a dipole antenna using 50 ohm coaxial cable. Connect one lead to the Antenna point and the other to the earth line.

You may experiment using 6V or 9V with the circuit to see how this increases the range of the transmitter. The sensitivity may be increased by lowering the 22K resistor to 10K. Try it and see. Note that this FM transmitter is not suitable for use on your body, for example, in your pocket. This is because it is affected by external capacitance and the transmitting frequency drifts depending how close you are to it. Stray capacitance is automatically incorporated into the capacitance of the tank circuit which will shift the transmitting frequency.

FM TRANSMITTER PARTS LIST

Constructing FM transmitters (89MHz - 109MHz)

2008-12-11T10:45:00.000-08:00

This project provides the schematic and the parts list needed to construct FM transmitters with an operating frequency of 89MHz - 109MHz. You need a receiver to receive the signals from this transmitter. Typical radio tuned to FM range will be able to receive this signal.

A Frequency Modulated wave is a sine wave with a periodically varying instantaneous frequency and a constant amplitude. The average frequency is called the carrier frequency and the instantaneous frequency changes at the modulation frequency . The maximum excursion of the instantaneous frequency from the average is related to the modulation depth .

For a FM radio transmission, the carrier frequency would be the station you tune to, and you would hear a pure audio tone at the modulation frequency, with a loudness derived from the modulation depth.

Frequency modulation (FM) is the encoding of information in either analog or digital form into a carrier wave by variation of its instantaneous frequency in accordance with an input signal. This is typically accomplished using radio waves. The most typical use is radio broadcasting.

Frequency modulation requires a wider bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against interference. Frequency modulation is also more robust against simple signal amplitude fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission: hence the term "FM radio". The FM modulation illustration is as shown in the diagram below.

When assembling the components into the PCB, be careful to cut the leads of components as short as possible because at high frequencies, leads will alter the capacitance and inductance of the circuits.

The output of the FM transmitters is approximately 9mW at 9V with the antenna tapped at position B. Tapping the antenna at position A will triple the range to 27mW.

You can find the CK217 9V FM Transmitters kit here under the SURVEILLANCE AND SECURITY (SPY) category.

Decoding Of Infrared Remote Control Software

2008-12-11T10:44:00.000-08:00

Infrared Remote Control Software

This Infrared Remote Control Software project based on Microchip 16C57 microcontroller is a reference guide to decode infrared remote control signals from television, VCR, air conditioner or other home appliances handset that uses NEC 6121 infrared format. Once one is able to understand how to decode an IR signal of a certain format, decoding another format can be easily done as the flow chart is more or less the same except the timing of the new format.

The NEC 6121 format is based on pulse width timing in determining whether the data transmitted is "1" or "0". The data "1" is determined by the pulse width timing from one rising edge to the next rising edge of 2.24ms. The data "0" is determined by the pulse width timing from one rising edge to the next rising edge of 1.12ms.

Most of the transmitter

are modulated using a frequency of 32.75 kHz, 35.0 kHz, 36.0 kHz, 36.7 kHz, 38 kHz, 39 kHz, 40 kHz, 41.7 kHz, 48 kHz, and 56.8 kHz. The ones that are commonly used are 38 kHz and 40 kHz. In order to decode the received signals, the corresponding demodulating receiver must be used. For instance, if a modulating frequency at the transmitter used is 40 kHz, then the receiver demodulating frequency used should be 40 kHz as well. Modulating the data is a better design as this will make the data integrity better and less susceptible to noise. The demodulating receivers can be obtained from suppliers such as Vishay, LiteOn, Sharp or Kodenshi.

One word of caution when using the IR remote control is that it is easily affected by lighting devices that emits the infrared frequency. One such example is the fluorescent tube which emits the infrared frequency in its operation

. When this type of lights is operating, the receiver may not be able to receive the signal from the transmtter due to interference from the signals emitted by the flurescent tube. In situation like this, confirm this by switching off the lights when controlling the device.

You may want to consider using RF frequency as a solution in this particular location. Another way is to place a filter in front of the receiver to narrow the infrared window but this solution will compromise the angle and operating distance of the infrared transmitter.

The infrared remote control software project provides the flow chart and source code and can be downloaded from Microchip website.

Build A Program Remote Control IR Transmitter Using HT6221/HT6222 IC

2008-12-11T10:42:00.000-08:00

Program Remote Control IR Transmitter

This project is based on integrated circuit from Holtek Semiconductor HT6221/HT6222. Similar parts used to be produced by NEC Semiconductor uPD6121/uPD6122. These ICs are commonly used in television and VCR infra red remote controls, garage door controllers, car door controllers, security systems and other remote control applications.

They are capable of encoding 16-bit address codes and 8-bit data codes. Each address/data input can be set to one of the two logic states, 0 and 1. The HT6221 can have keys up to 32(K1~K32) and HT6222 64 keys (K1~K64). When one of the keys is triggered, the programmed address/data is transmitted together with the header bits via an IR (38kHz carrier) transmission medium.

This project provides the transmitter part of the remote control. Designers and hobbyists will have to do their own software at the receiver board. Those who are familiar with microcontroller programming will find this device easy to use. The features of this IC are:

Operating voltage: 1.8V to 3.5V DC
Data output with 38kHz carrier for IR medium
Low standby current
455kHz ceramic resonator or crystal
16-bit address codes
8-bit data codes
Pulse Position Modulation code method

Program Remote Control Circuit Description

The typical 32 pins HT6221 schematic is as shown above. However, the values of 1k ohm and 47 ohm at the output pin 5 of the IC can be reduced to increase the distance the IR signal is transmitted. After the transmission codes are sent, the DOUT pin generates transmission codes with a carrier, and the LED goes low to drive a transmission indicator.

When one of the keys is triggered for over 36ms, the oscillator is enabled and the chip is activated. If the key is pressed and held for 108ms or less, the 108ms transmission codes are enabled and comprised of a header code (9ms), an off code (4.5ms), low byte address codes (9ms-18ms), high byte address codes (9ms-18ms), 8-bit data codes (9ms-18ms), and the inverse codes of the 8-bit data codes (9ms-18ms).

After the pressed key is held for 108ms, if the key is still held down, the transmission codes turn out to be a composition of header (9ms) and off codes (2.5ms) only.

Logic 0 is represented by timing 1.12ms and logic 1 by timing 2.24ms using pulse position modulation method as shown below.

The address code and data codes are set using the diodes 1N4148 and resistors 51K ohm and whether D7 is connected to Vcc or Ground.

The complete specifications of the Program Remote Control IC HT6221/HT6222 can be downloaded here.

How to construct a Infra Red Wireless Door Monitor

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Monitor Project

This door monitor project uses an infrared beam to monitor door & passageways or any other area. When the beam is broken a relay is tripped which can be used to sound a bell or alarm. Suitable for detecting customers entering a shop, cars coming up a driveway, etc. The IR beam is very strong. Distances over 25 feet can be monitored. A 12VDC supply is required to power the circuit. A 12V wall adaptor is fine. Provision has been made so that only one power supply needs to be used to power both units. The relay is rated to switch mains voltages.

Door Monitor Transmitter Board

The door monitor transmitter board consists of two square-wave oscillators, one running at approx. 250Hz and the other running at 38kHz. The 38kHz frequency acts as a carrier wave and is required by the IR receiver module on the receiver board. This carrier wave is “ANDed” or modulated by the 250Hz frequency to produce an output signal that contains bursts of 38kHz at a rate of 250Hz. This signal is used to drive an infrared LED. The oscillators are made by using two 555 timer ICs set up as “astable” (free running) multivibrators. IC1 is used for the 250Hz oscillator. Resistor R1 and R2 and capacitor C1 set the frequency. Another 555 chip, IC2, is used for the 38KHz oscillator. Resistors R4 and R5 and capacitor C3 set the frequency. Notice the diodes D1 and D3. These are provided to create a “symmetrical” output. Normally the external capacitor C1 (C3) charges through resistors R1 and R2 (R4 and R5) and discharges through R2 (R5). Without the diodes this output waveform would have a longer “high” time than the “low” time. The diode bypasses resistor R2 (and R5) when the capacitor is charging, so that it is only charged via R1 (or R5). This gives the same charging and discharging time and so the output waveform has equal high and low times.

The charge time (output high) is given by:

THIGH = 0.693 x R1 x C1 (or 0.693 x R4 x C3)

The discharge time (output low) is given by:

TLOW = 0.693 x R2 x C1 (or 0.693 x R5 x C3)

The output frequency = 1 / (THIGH + TLOW)

The output from the IC1 is coupled via diode D2 and resistor R3 to the ‘trigger’ input of IC2. When the IC1 output is low it stops IC2 from running and IC2’s output is forced high (no IR LED current). When IC1 output is high, IC2 runs and the IR LED is pulsed at 38KHz.

The Waitrony IR LED is driven directly from the output of IC2. Resistor R6 sets the maximum LED current. With a 12VDC supply the current is about 45mA (the LED drops 2V across it when conducting). Lowering the value of R6 will increase the current through the LED thus boosting the signal strength. This may be necessary if the kit is used outside in direct sunlight or if you need “very long range”. Keep in mind that the maximum current that the 555 can handle is 200mA

If the distance to be monitored is less than about 10 yards then you will need to fit the 5mm shrink tubing over the IR LED. This narrows the radiating angle of the IR beam and makes it much more directional. The IR output is strong. It can easily bounce off walls etc to give false readings.

Door Monitor Receiver Board

The door monitor receiver consists of an IR receiver module that detects the incoming IR beam from the transmitter. The IR signal is used to keep a capacitor charged which in turn holds a relay operated. When the beam is broken the capacitor discharges and the relay releases. An IR receiver/detector module, RX1, is made up of an an amplifier/filter circuit tuned to detect a 38kHz frequency. The output pin is low whenever a 38kHz signal is detected.

When the IR beam is present the relay is operated. Not all Receiver Modules are the same. IR decoder module looks for a manufacturer-specific leader code before it decodes the modulated signal. The door monitor project produces an NEC compatible Leader code. The Kodenshi PIC37043LM and PIC12043LO decoder modules are the ones that are used in this project. If you use the incorrect IR decoder module the relay will not be operated continuously but will drop out after less than a second after power is applied.

The output of RX1 is the 250Hz signal from the transmitter. This signal is passed via transistor Q1, capacitor C1and diode D2 to capacitor C2. C2 is fully charged during the high portion of the signal. It starts to discharge during the low portion of the signal via LED L1, resistor R4 and transistor Q2. However the discharge time is much longer than the off time of the signal so the voltage across C2 is always enough to keep transistor Q2 on and therefore the relay operated. When the beam is broken the output of RX1 is high. Transistor Q1 is off and capacitor C2 is no longer being recharged. It will eventually discharge to the point where transistor Q2 will turn off and the relay will release. The “turn off” delay is determined by the time constant of resistor R5 and capacitor C3. With the values used it is approx. half a second. Capacitor C1 prevents a steady DC voltage on the collector of Q1 from charging C2. This would occur if the beam was not present or the beam was a continuous 38kHz signal. In other words, the receiver module will only respond to a pulsed 38kHz signal.

LED L1 gives a visual indication when the IR beam is present and is used to help with installation and setup. Zener diode Z1, resistor R6 and capacitor C4 provides a stable 5.6V supply for the IR module. The relays used should be mains rated: 250V/12A; 120VAC/15A.

Door Monitor Parts List

RFID Application

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Application Introduction

RFID or Radio Frequency Identification is the use of any device that can be sensed or detected wirelessly through the use of radio frequency technology. RFID application has been used in many applications

ranging from tagging of library books and assets, electronic toll collection system, healthcare, security access system and many other applications. A typical RFID system consists of a transponder where a microchip with an antenna is embedded in an item. A reader with antenna is used to read data or write data to the transponder wirelessly. The data read is then passed to a computer where it is used for business transactions.

A study shows that the market for RFID application in the year 2001 was USD1 billion and expected to reach USD4.6 billion by the year 2007. In the past, the cost of RFID tags was an obstacle to its use in mass quantity. However, as the wireless technology becomes more readily available and cheaper due to its demand in the global market, its use is expected to rise at a rate not imagined before.

There are basically 2 types of RFID in use today. They are passive and active types with frequency ranging from 125kHz to 2.45GHz.

Passive Type

The passive tags do not have any transmitter and obtained its power supply from the electromagnetic waves emitted by the reader. This type of tags are cheaper and could range from 15 cents to 50 cents and require minimal maintenance. They have operational range of a few inches to 30 feet. The frequency used can range from 125kHz to 2.45GHz depending on the applications but usually lower frequencies components are cheaper. Passive tags are used in retail business and manufacturing processes.

Active Type

The active tags have transmitter and its own power source. The power source can be solar energy, batteries or from other sources. The transponder is able to communicate with the reader without getting the power supply from the reader. The range of communication is from 60 feet to 300 feet with higher frequencies used. Frequencies used are 455MHz to 5.8GHz.

The application of active type is in large inventory assets control and containers where they need to be tracked over a larger area or distance. Another application is in electronic toll collection system where the transponder will be active when it received a signal from the reader. It then communicates with the reader and do the necessary transactions after which it will go back to sleep or idle mode. In this way, the lifetime of the batteries used in the transponder is extended.

The RFID passive type where a frequency of 13.56MHz is used in its development can be obtained from RFID Application - Passive 13.56MHz Application Note Microchip website.

Electronics Hobbies Projects Schematics and Parts List References

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Color Sensor

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Color Sensor Click here for the circuit diagram

Colour sensor is an interesting project for hobbyists. The cir- cuit can sense eight colours, i.e. blue, green and red (primary colours); magenta, yellow and cyan (secondary colours); and black and white. The circuit is based on the fundamentals of optics and digital electronics. The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered. The circuit makes use of only ‘AND’ gates and ‘NOT’ gates.
When a primary coloured light ray falls on the system, the glass plate corresponding to that primary colour will allow that specific light to pass through. But the other two glass plates will not allow any light to pass through. Thus only one LDR will get triggered and the gate output corresponding to that LDR will become logic 1 to indicate which colour it is. Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corres- ponding to the mixed colour will allow that light to pass through while the remaining one will not allow any light ray to pass through it. As a result two of the LDRs get triggered and the gate output corresponding to these will become logic 1 and indicate which colour it is.
When all the LDRs get triggered or remain untriggered, you will observe white and black light indications respectively. Following points may be carefully noted :
1. Potmeters VR1, VR2 and VR3 may be used to adjust the sensitivity of the LDRs.
2. Common ends of the LDRs should be connected to positive supply.
3. Use good quality light filters.
The LDR is mounded in a tube, behind a lens, and aimed at the object. The coloured glass filter should be fixed in front of the LDR as shown in the figure. Make three of that kind and fix them in a suitable case. Adjustments are critical and the gadget performance would depend upon its proper fabrication and use of correct filters as well as light conditions

Battery Tester Project

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Project Using LM3914 IC

This objective of this project is to design and build a battery tester that is able to test various types of dry cell and rechargable battery with a voltage of less than 2V. Configured as a bar graph battery level indicator, the LM3914 IC from National Semiconductor senses the voltage levels of the battery under test and drives the 10 LEDs to ON or OFF based on the voltage that is detected. The current driving the LEDs is regulated by using the external resistor R1 and hence limiting resistors are not required.

The schematic shows the simple connections where the reference voltage at pin 8 of U1 can be adjusted by adjusting the variable resistor VR1. The voltage at pin 8 will set the maximum scale of the LED. In testing dry cell battery of 1.5V, set the voltage at pin 8 to 2.0V. Each of the LED will thus represent 200mV when lighted up.

If testing of rechargable battery such as NiCd or NiMH is required, set the reference voltage to a lower value such as 1.5V as the typical voltage of a rechargable battery is approximately 1.2V.

When testing the battery, take note of the polarity of the probe to the terminals of the battery. T1 is to be placed on the positive terminal and T2 the negative terminal of the battery.

Parts List

The parts list of the project is as shown below.

Constructing TTL/CMOS Logic Probe

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The purpose of a logic probe is to examine the logic states at a particular point in an electronic circuit. It is usually used in fault finding and testing but it can also be used to find out how a piece of electronic equipment works or to assist in electronic design. There are many circuits for this type of probes. Some are very simple while others have added so many features the probe has become too big. At a minimum any probe should be usable with both CMOS and TTL logic families. In this design a pulse detection circuit has been added because the detection of electronic pulses is so important today in many electronic circuits.

Logic Probe Circuit Description

1. There are two main logic families used in electronics: CMOS and TTL. For CMOS the supply voltage may be anywhere between 3V and 15V and the logic levels used are taken as a proportion of the supply voltage. Levels quoted by different manufacturers vary so the the probe should be calibrated for the most extreme cases.)

For CMOS the extreme limits are:

HIGH -- greater than 73.3% of supply voltage

LOW -- less than 26.6% of supply voltage

For TTL the supply voltage should be 5 volts and the logic levels are:

HIGH -- greater than 2 volts

LOW -- less than 0.8 volts

At a minimum a logic probe should be usable over the full range of CMOS circuit voltages. In practice this is from 5V to 15V. If the probe takes its power supply from the circuit under test (as most do) then all components in the probe must operate over the 5 to 15 volt range. Some electronic equipment may have different voltage circuits within it so you must connect to the correct one that you want to test. A good logic probe should be able to detect both positive and negative pulses. It should be able to detect the brief pulses which can switch CMOS and SCR devices. The minimum width of these pulses is of the order of 50 ns (50 nano seconds, 50 x 10-9 seconds.) In this project we have incorporated a high speed, dual polarity pulse detection and stretching circuit which can capture these pulses. Detection is no good without audible and visual indication of what is detected. Audible indication is necessary so that you do not have to take your eyes off where you are working with the tip of the probe. Three different coloured 3mm LED's give a visual indication. The table gives the various combinations of logic levels and pulse widths which can be detected.

2. Logic Probe Circuit Description - Level Detector.

This circuit consists of a dual op-amp and two resistor divider networks which can be selected by a switch. One network selects the voltage levels for CMOS, the other for TTL. The resistor dividers are not protected because the nonlinearity of the diode would affect the level references. The LM358 wide range, single supply, dual op-amp was selected so that it can operate over the full range of CMOS supply voltages. Amp A detects the high level. The inverting input (pin 2) is set to the high level reference. If the noninverting input (pin 3) rises above that level then the output (pin 1) switches to high. This high activates the high level indicators until the level of the input signal is reduced below the high level reference. Amp B performs a similar function for the low level. This time it is the noninverting input (pin 5) that connects to the reference. Accordingly the amp switches high when the input from the probe (pin 6) falls below the low level reference. The low level indicators are then activated until the input voltage is raised above the low level reference again.

3. Logic Probe Circuit Description - Pulse Detector.

This circuit consists of 4 CMOS inverters (in the 4049/14049) and some passive components. Start at pin 7. Usually R15 holds pin 5 low which makes pin 4 high, which in turn makes pin 7 high via diode D4 leakage. If pin 7 is pulled down by a negative pulse from C2 or C3 the pulse travels through the first inverter (and becomes high), then to C4 and the second inverter to arrive at pin 4 as a low. The low holds pin 7 low via diode D4. Pin 6 is now high. Pin 5 is therefore held high until C4 discharges through R15. When pin 5 falls to the CMOS low level pin 4 goes high again and the latch is released. The pulse indication time is set by the time constant C4.R15. When a pulse is detected it is stretched to about a second during which time the orange LED is turned on and a tone sounds. The tone will be a medium tone unless the final level is low. In this case the tone will be a low pitch. Before the pulse detector circuit are two inverters. They perform a number of functions. They shape the level change into a sharp pulse and put out signals at rail voltage. Any change of level (low to high or high to low) at the probe will cause one inverter to go high and the other to go low. By adding the diodes D2 and D3, when a level change occurs the output going from low to high is blocked temporarily until its leakage current charges the 100pF series capacitor. However, the output going from high to low is not blocked because its diode is then forward biased and a negative going pulse arrives at pin 7. As describes in the previous paragraph a negative pulse at pin 7 causes a pulse detection signal. If the input to the logic probe is not in a defined state (that is, if it is in the range 26.6% to 73.3% of the supply voltage for a cmos circuit, or 16% to 40% of the supply voltage for a TTL circuit) then it is in the floating level. However, the cmos gate connected to the probe will still recognise the input as high or low. Normally it will switch at 50% so normally we could call 26.6% to 50% of the supply voltage floating low, and 50% to 73.3% floating high. The implications of this are:

a) that pulses to and from the floating range will only be detected if they cross the switching level for the cmos gate.

b) that TTL pulses to marginal positive levels may not be detected by the pulse detector (but will still show up on the level detectors if they are not too fast)

c) that the pulse detectors will show what users usually want to know, namely whether any transients are going to cause switching in cmos devices. If the probe is floating (that is have an undetermined input) then it will be floating either high or low. If it is floating high then it will not detect a positive going pulse because it is not a true pulse as far as the probe is concerned. Similarly, if it floating low then it will not detect a negative pulse. All these conditions are illustrated in the table and diagrams as below.

4. Logic Probe Circuit Description - Indicators.

The visual indicators are provided by the LED's. The audible indicators are provided by an audio frequency relaxation oscillator driving a piezo element via CMOS inverter buffers. The relaxation oscillator consists of a PUT (programmable unijunction transistor) fed by a variable time constant supply. The PUT acts like an open circuit if the gate voltage is higher than the anode voltage. It avalanches to a short circuit if the anode voltage reached the gate voltage. If any of the indicator signals are high the high charges C5 through the corresponding resistance (R12, R13 or R14.) When the PUT triggers it discharges C5 which restores the PUT and charging recommences. The resistance in the charge circuit determines the charge time which in turn determines the oscillator tone.

HOW TO USE THE LOGIC PROBE

Determine the supply voltage of the logic elements to be tested. Connect the positive and ground (or negative) leads correctly. Place the tip of the probe on the point you want to test. If the circuit has switches to control its operation and you want to see what happens when you change settings hold the probe in place while you make the changes. Be careful not to short out components on the board under test. The indicators will tell you if you are in the immunity band (no signal.) A HIGH level will bring on the RED LED and a high pitched sound. A LOW level will bring a low pitched sound and the GREEN LED. A fast pulse will light the YELLOW LED and a medium pitched sound for about a second. A slow pulse will combine the fast pulse signals with a pulse of the relevant level indicators. A level change will combine the pulse signals with the relevant leval signal. If the level change is very slow the pulse signal may not coincide with the start of the level signal. The Table on the next page lists the typical states and transitions that the logic probe will detect. The Conditions are shown the Diagrams.

LOGIC PROBE ASSEMBLY INSTRUCTIONS

LOGIC PROBE assembly is straight forward and components may be added to the PCB in any order. Note that there are two links to be added to the PCB. The metal probe for the Logic Probe must be soldered to the large pad where indicated underneath the PCB. Use a cut piece of wire from one of the resistors as the probe, Power for the probe is derived from the circuit under test. The GROUND and POSITIVE pads at the right side of the PCB are where power is connected to the board. Two tie holes have been drilled next to each pad so that the wires may be tied down and reduce mechanical strain on the wires as the probe is moved around during use.

Electronic Design Circuits Touch Switch

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Electronic Design Circuits Touch Switch

In this Electronic Design Circuits Touch Switch project, a CMOS quad 2 input NOR gate IC is used as a latching circuit to switch a LED ON and OFF by physically touching the ON metal plate or OFF metal plate. The CD4001BC integrated circuit is a monolithic complementary MOS (CMOS) IC that are constructed with N- and P- channel enhancement mode transistors. Its input are protected against electrostatic discharge with diodes to VDD and VSS.

The circuit below shows the schematic diagram of the touch circuit of which the NOR gates are configured as a simple latching circuit. When the skin contact is made between contacts T1 and T2 or T3 and T4, the LED switches ON and OFF respectively. The latching circuit is to ensure that the output will not fluctuate between ON and OFF.

When the T1 and T2 contacts are bridged through the skin contact, the output of U1-a will go to logic "0" and caused the output of U1-b to go to logic "1". This output will in turn caused NOR gate U1-c to go to logic "0" causing transistor Q1 to turn ON, and hence LED will turn ON. The circuit will remain latched with the LED ON until contacts T3 and T4 are bridged of which the output of U1-a will go to logic "1", output of U1-b will go to logic "0", output of U1-c will go to logic "1" and the transistor Q1 will turn OFF. The LED will then turn OFF.

It is important to ensure that 9V battery is used as its DC source. If one uses the mains supply to step down the voltage using a transformer for rectification and filtering to get the 9V DC supply, ensure that the transformer is designed in such a way that it follows the safety standard requirement of UL. This is important to ensure the safety of the user that is using the metal contacts to ON/OFF the LED.

Parts List

Construct 3 1/2 Digit LED Panel Meter Using Intersil 7107 LED Drivers

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Introduction To LED Panel Meter with LED Drivers

The Intersil ICL7107 is a low power, 31/2 digit A/D converters that is used to drive LED displays. Other features included in the IC are seven segment decoders, display LED drivers, a reference, and a clock. It is able to directly drive an instrument size light emitting diode (LED) display.

It features autozero to less than 10µV, zero drift of less than 1µV/Celcius, input bias current of 10pA (Max), and rollover error of less than one count. True differential inputs and reference are useful in all systems, but give the designer an uncommon advantage when measuring load cells, strain gauges and other bridge type transducers.

Voltage is the most frequently measured electrical quantity. In this General Purpose 3 1/2 Digit LED Panel Meter, voltage is being measured to find out the temperature, current, wind speed, resistance or lux etc. After calibrating the meter for its particular purpose the voltage measured will give an accurate digital reading of the analog quantity being measured.

Circuit Description of the 7107 LED_Drivers

Figure below shows the schematic design of the 7107 LED_Drivers.

-5V Generation

The 7660 IC is used to do voltage conversion from positive to negative for an input range of 1.5 to 10V, resulting in complementary output voltages of -1.5V to -10V. The -5V DC supply is needed to power up the 7107 IC on top of the +5V DC.

7107 IC with LED Drivers

The heart of the meter is the analog to digital converter built into the 7107 LED Drivers . It uses a dual slope conversion technique. It uses the charging and discharging of an integrating capacitor and having a counter count when the capacitor voltage is above a set value. There are three phases to the process:

Phase 1. Auto Zero.

The autozero capacitor is charged to the integrators offset voltage. This voltage is subtracted from the input signal during phase 2. The integrator thus appears to have zero offset voltage.

Phase 2. Signal Integrate.

The signal input is averaged for 1000 clock pulses.

Phase 3. Reference Integrate.

Input low is internally connected to Common (which may be an offset voltage.) VREF is averaged back to either zero volts or the offset voltage over another 1000 clock pulses. The number of clock pulses counted to return to this value is a digital measure of VIN.

System Timing of 7107 LED Drivers

This is determined by the components connected to pins 38, 39 & 40. The internal oscillator runs at 48kHz.

Decimal Point of 7107 LED Drivers

A jumper selects the decimal point position in the displays that is driven by the LED Drivers.

Analog Section

C1 is the reference capacitor and is unchanged for all ranges measured. IN LO is tied to the analog COMMON pin 32 by the Normal position of the switch except when an Offset voltage is input. The integration capacitor C5 is suitable for all ranges measured but the value of the integration resistor R1 should be increased to 470K for a VREF of 1V.

Auto-Zero Capacitor

This is C4 connected to pin 29. It has some influence on the noise of the system and recovery from overload input. On the 2V scale a 0.047uF capacitor may give better results.

Voltage Measurement

Since the maximum value which can be displayed is 1999, voltmeters with full scale readings of 199.9mV, 1.999V, 19.99V etc. can be made.The user must decide their own need. Then a reference voltage and maybe an input attenuator must be selected. To use the meter to measure 0 - 199.9mV the trimpot is adjusted so that the reference voltage between pins 35 & 36 is 100mV. And to set the meter for 0 - 1.999V, VREF must be set to 1.0V. Measuring higher voltages and nonstandard voltages will be discussed below. The relationship between full scale input voltage and the reference voltage is:

VIN = 2 x VREF

VREF must be in the range 100mV to 1.0V. For a VREF of 1V two components should be changed (R1=470K, C4=0.047uF) to maintain sensitivity and recovery from over-voltage. The 10K trim pot and resistor R3 will allow adjustment for either value, and for intermediate values when required (discussed below.) The following discussion will be using a VREF of 100mV.

Calibration is done by attaching a multimeter to REF HI and REF LO and adjusting the trimpot to read 100 mV. will calibrate the meter to read 0 - 199.9mV.

Voltage Divider

In order to measure voltage greater than 0.2V, an input voltage divider is required. This is the purpose of 4 resistors on the main circuit board. The general relation for full scale sensitivity is now:

VIN (full scale) = 2VREF x RY / ( RX + RY)

For example, a 0 - 20V range (when VREF is 0.1V) can be obtained using a 100:1 voltage divider. This can be done by making RX = 1M and RY = 10K. The decimal point jumper is placed at position '2' so a full scale display of 19.99V is indicated. Similarly, a 0 - 200V range can be obtained with RX = 1M and RY = 1K.

If VREF is 1V a similar pattern of voltage divider resistors can be determined. Remember that if no input divider is used, put the 10M resistor back in RY1 across the input leads.

Input an Offset Voltage

A major advantage of a 7107-based meter is that an offset voltage may be read directly by the 7107. Offset input voltage is used by moving the switch the 'Use Offset' position. The offset voltage is input to pin 32, Offset, and pin 30, In Lo, while the transducer is connected as normal using Input 2 and Input 3.

Non-standard Voltage Input

In many applications it is required that the output of a transducer is converted by a scale factor into some meaningful result. For example, a load cell of a weighing system may have an output voltage of 0.682V when it has 2.0 Kg weight on it. You want the meter to read the range 0 - 1.99 Kg directly. It is an easy matter to adjust VREF to 0.341V (half the output voltage), put the decimal point in the correct position by moving the jumper and the panel meter now reads off 0 - 1.99 Kg directly from the display.

Current Measurement

Currents up to 2A can be easily measured using a 5W shunt resistor, R. The current is converted into a voltage by the shunt resistor. The voltage divider resistors RX and RY (including RY1) are not used. The principal is shown in Figure below.

If R = 0.1 ohms then 200mV will be developed when the current through it is 2A. This voltage is applied to the meter which is set up for the 200mV range. (That is, VREF is set to 100mV.) Power disspiation at the maximum reading is IXIXR which is 0.4W, well within the 5W rating of the resistor.

To measure a full scale of 200mA then R should be 1.0 ohms in order to generate 200mV input to the meter. For a 20 mA meter then R = 10 ohms. Note that because of wide tolerances in the shunt resistors it may be necessary to adjust the reference voltage in order to get the correct reading. So further adjustment of VREF using a known current may be required.

A very good and detailed writeup and application on 7107 from Intersil can be found in the following link.

7107 LED Drivers Project Data Sheet

Project Application Note

Parts List of 7107 LED Drivers Project

Touch Switch/Contact Switch Free Electronic Circuits

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Touch Switch
Free Electronic Circuits

The main part of the Touch Switch Free Electronic Circuits are the two NAND gates of the 4011 Integrated Circuit which are connected as a flip-flop. Pins 9 and 13 are the ON and OFF contacts. The two gates are connected to the positive rail by the two 10M resistors. Shorting one of the gates with the ground rail by touching it (this is equivalent to connecting about 50K between the gate and ground) FLIPs the output to that state. Shorting out the other contact FLOPs it back.

The output of the flip-flop drives a transistor connected as a switch. It switches an LED and a relay. The relay is a 12V relay and commonly available SPDT type 240VAC can be used to switch ON or OFF a lamp or other electrical appliances. However, make sure that the current and voltage of the device are within the contact relay specifications. Connecting the two 1K resistors connects the other two NAND gates of the IC into the flip-flop and makes it much more sensitive to touch. The touch plate may in fact work with only the first two gates connected. But it will be much more sensitive with all four gates connected as a flip-flop.

Ensure that an isolating transformer is used when the power supply comes from the mains before being rectified to 12V DC for safety purposes. The schematic diagram of the circuit is as shown below.

Parts List

Touch Switch And Delay Circuit Using 555 Timer IC

2008-12-11T10:27:00.001-08:00

Touch Switch
And Delay Circuit Description

In this simple touch switch circuit, the 555 timer is configured as a one shot multivibrator that is triggered by touching the touch terminal.

In this monostable mode, the timer generates a fixed pulse of about 4 seconds whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C2 and setting the flip-flop output at the same time.

The voltage across the external capacitor C2, VC2 increases exponentially with the time constant t=R3*C2 and reaches 2Vcc/3 at td=1.1R3*C2. Hence, capacitor C2 is charged through resistor R3. The greater the time constant, the longer it takes for the VC2 to reach 2Vcc/3. In other words, the time constant R3*C2 controls the output pulse width. When the applied voltage to the capacitor C2 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the discharging Tr. on. At this time, C2 begins to discharge and the timer output converts to low. In this way, the timer operating in the monostable repeats the above process.

To increase the time of the delay from 4 seconds, the value of R3 and C2 need to be increased. Similarly, to decrease the output time delay, the value of R3 and C2 need to be reduced.

The output from the 555 timer can be used to drive a transistor which in turn can drive a delay to control device like lamp, and other equipments.

Parts List

3 Digit Counter Electronic Project Schematic

2008-12-11T10:25:00.002-08:00

3 Digit Counter Electronic Project Schematic

The 3 Digit Counter Electronic Project Schematic uses two 14553 IC's. The 14553 is a 3-digit BCD (binary coded decimal) counter. Inside the chip, each counter drives a 4-bit latch which quad 3 input multiplexer. The chip has Carry, Reset, an input clock and Latch Enable. The 1nF mylar capacitor on pins 3 and 4 sets the multiplex scan rate to about 1 kHz.

The four outputs (Q0 to Q3) are fed into the 14511 cmos 7-segment decoder driver. The outputs of this driver then go to the 3-digit multiplexed display unit. Each digit is turned on at the correct time via the display control outputs at pins 2, 1 and 25 of the 14553. They are active low outputs. Each drives a BC557 pnp transistor via a 4k7 resistor. The transistors in turn switch the common cathode of the digits in the display.

The counter module is a typical debounce circuit. The resistance and capacitor provide a delay period during which the noise of the switch connection will not register a 'count'. The hatkey switch used are very noisy switches but this debounce circuit take care of the problem for as fast as manual pressing will allow. Digital inputs from other sources may be routed through the board but the debounce circuit will have to be changed if the input frequency is higher than 100 to 150 Hz (cycles / second.)

Further detailed of the Electronic Project Schematic 14511, 14553 and 14093 specifications can be obtained from ON Semiconductor website.
Parts List

Voltage Detector Electronic Circuit Project

2008-12-11T10:25:00.001-08:00

Voltage Detector Electronic Circuit Project

This circuit is using a LM339 quad comparator as its operation. Four variable resistor or potentiometers are used to allow individual settings for each section of the comparator. Four LEDs are connected to the output to indicate the status of the input level. If the circuit is duplicated, and the inputs connected together, the resolution of the voltage detector will be double and more readings can be set.

The LM339 consists of four independent precision voltage comparators with an offset voltage specification as low as 2 mV max for all four comparators. These were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. These comparators also have a unique characteristic in that the input common-mode voltage range includes ground, even though operated from a single power supply voltage.

Further detail of the specifications can be obtained from Electronic Circuit Project National Semiconductor website.

This circuit can be used as a bargraph voltmeter with each potentiometer set for a specific voltage.

Parts List

Basic Electronic Project - Variable Frequency Audio Oscillator Using MC34119

2008-12-11T10:24:00.000-08:00

Variable Frequency Audio Project

This basic electronic project can be used as a low level alarm generator or a code practice oscillator. It is centred around MC34119 IC which is a low power audio amplifier

. It provides a differential speaker outputs to maximize output swing at low supply voltages(2.0 V minimum). Coupling capacitors to the speaker are not required. It has the following features.

a) Wide Operating Supply Voltage Range. (2.0 VDC to 16 VDC)
b) Low Quiescent Supply Current (2.7 mA Typ) for Battery Powered Applications.
c) Chip Disable Input to Power Down the IC.
d) Low Power–Down Quiescent Current. (65 mA Typ)
e) Drives a Wide Range of Speaker Loads. (8.0 W and Up)
f) Output Power Exceeds 250 mW with 32 W Speaker.
g) Low Total Harmonic Distortion. (0.5% Typ)
h) Gain Adjustable from <0>46 dB for Voice Band.
i) Requires Few External Components.

The schematic below shows the basic schematic of the project. In this circuit, the output of MC34119 at pin 8 is fed back to input at pin 4 through the RC network. This controlled positive feedback causes the amplifier to go into oscillation. The frequency of oscillation can be varied from 250 Hz to 4 kHz using the 50K potentiometer

VR1. The chip disable input pin 1 is kept high using the R2 resistor. As long as this pin is high, the amplifier does not operate. Once it is pull to ground by the key K1, the oscillator will turn ON. This circuit can be modified to suit any application that needs to sound an alarm when a certain event happen by controlling the key K1 electronically.

Parts List

2008-12-11T10:23:00.001-08:00

Free Electronic Project Schematics - Audio Signal Tracer Circuit

This schematics function is to enable one to trace an audio signal through a maze of wires running around the house.

As shown in the schematic above, when a inductor coil L1 is brought near the wire carrying the audio signal, the audio signal will be induced into the coil and the signal is fed to the inverting input of op-amp IC1-a. It is then amplified by and the amplified output is fed to IC1-b iverting input. The second op-amp increases the signal level to drive a set of low impedance headphone, Z1.

The coil L1 is made by using a size #30 enamel coated copper wire wound on a 1.25 inch length of a 0.25 inch diameter ferrite rod. Use a turn of appoximately 80 to 100 turns. It can be located several feet from the circuit and connected it through a shielded cable.

Parts List

The parts list is as shown below.

Source : Extracted from Popular Electronics
Feb 1993, By Charles D. Rakes

Free Electronic Project Schematics - Audio Signal Tracer

2008-12-11T10:23:00.000-08:00

Free Electronic Project Schematics - Audio Signal Tracer Circuit

This schematics function is to enable one to trace an audio signal through a maze of wires running around the house.

Parts List

The parts list is as shown below.

Source : Extracted from Popular Electronics
Feb 1993, By Charles D. Rakes

Melody Music Generation Using M348X CMOS IC

2008-12-11T10:14:00.000-08:00

Music Generation Project

The M348X series is a mask-ROM-programmed multi-instrument melody generator , implemented by CMOS technology. It is designed to play the melody according to the previously programmed information. The device also includes a pre-amplifier which provides a simple interface to the driver circuit. The M348X series is intended for applications such as toys, door bells, music box, melody clock/timers and telephones.

This project based on the M348X IC is the electronic equivalent of a mechanical music box. It has a range of tunes and is activated by light falling on a light dependent resistor (LDR) sensor. It can be placed anywhere that you want a tune to play when light falls on it: a cupboard, music box. There could be some applications

where the LDR is replaced by a switch or a push-button.

Christmas music is available when M3481 is used.

Jingle Bells
Santa Claus Is Coming To Town
Silent Night, Holy Night
Joy To The World
Rudolph, The Red-nosed Reindeer
We Wish You A Merry Christmas
O Come, All Ye Faithful
Hark, The Herald Angels Sing

The following music is available when M3485 is used.

The Hawaiian Wedding Song

Try To Remember
Aloha OE
Butterfly Love Story
Yesterday

Melody Music Generation Description

When light falls on the LDR, the music IC is enabled by the positive potential appearing on pin 2. The sensitivity of the LDR can be changed by varying the value of the 100K in the SIL connected to pin 2. A tune is selected by pushing the PCB-mounted tact switch. The jumper J1 determines whether the selected tune will play continuously or will cycle through all the tunes available in the IC. The musical pitch is determined by the resistor R1. Decreasing the value of R1 lowers the pitch, and each tune takes longer to play. The RC network at pin 7 shapes the sound. The speaker is driven by a complementary pair of transistors driven by the IC. Negative feedback is provided by R3 to stabilise the DC voltage at the emitters of Q1 & Q2.

Jumper J2 selects whether or not a tune stops immediately when light is removed from the LDR, or it plays right through to its end before stopping. In the idle state the circuit draws about 50uA, and about 20mA when it is operating. Therefore, there is no need for an off/on switch.

Melody Music Parts List

The parts list for the project is as shown below.

Alarm Generator Project Using UM66TXXL CMOS IC

2008-12-11T10:12:00.000-08:00

Melody Music Project Description

This simple alarm generator electronics circuit utilizes a UM66TXXL TO92 package CMOS IC that generates song depending on the type of IC used. It has a built in oscillation circuit and need only a few external components to make it work. It is powered by a power supply range from 1.5V to 4.5 V DC with low power consumption, hence a longer battery lifetime. Once it power on reset, the melody will begin to sound. The part number for different songs are as listed below.

UM66T05L Home Sweet Home
UM66T11L Love Me Tender
UM66T19L For Alice
UM66T32L COO COO waltz

The IC can be used to drive a buzzer directly or driving a speaker though the use of a transistor.

Parts List

Message Recorder Digital Electronics Project

2008-12-11T10:10:00.000-08:00

Introduction

The purpose of this digital electronics project is to record messages using a dedicated voice recorder integrated circuit. Recordings are stored in a non volatile memory cells, which means that the message will still be saved even though power has been removed from the device.

Winbond’s ISD2500 Series provide high-quality, single-chip, Record/Playback solutions for 60 seconds to 120 seconds message applications. The CMOS devices include an on-chip oscillator, microphone preamplifier, automatic gain control, antialiasing filter, smoothing filter, speaker amplifier, and high density multi-level storage array. In addition, the ISD2500 is microcontroller compatible, allowing complex messaging and addressing to be achieved. Recordings are stored into on-chip nonvolatile memory cells.

Circuit Description

The ISD25120 has several modes of operation. The mode used here is as a multi-message recorder. You may record as many messages as you want up to 120 seconds of memory space.

Put the SPDT switch into the Record position and just push & release the Start/Pause button to start recording. The Record LED goes on. Push the Start/Pause button to Pause - stop recording. That is the end of Message 1. Sometime later you can record a follow on message, Message 2, by pushing the Start/Pause button again. When you put the switch to Play the messages will playback. Only one message will be played back at a time. You must push Start/Pause again to get the next message. The Reset switch will move the internal address pointer back to the start of the memory space.

Parts List

The parts list of the message recorder is shown as below.

The complete specifications of the Winbond ISD25120 IC can be obtained from ISD25120 Digital Electronics Project Specifications.

Digital Dice Project

2008-12-11T10:07:00.000-08:00

Digital Dice

This digital

dice project is an interesting project that will display in random the number from 1 to 9 on the 7 segment display. This is an alternative device that can be used to replace the traditional dice when you are playing games such as snake ladder, monopoly etc. The generation of clock is done by using a 555 timer which is connected in the astable mode at a frequency of approximately 50 Hz. This clock signal is fed into the decade counter which outputs are connected to 4 bit binary adder which provides a binary output equavalent to binary input + 1. The outputs are then connected to a BCD to 7 Segment Decoder which is used to drive a common anode 7 segment display.

As shown in the schematic above, when push button PB is pressed, a square output will be generated from the 555 timer which gives a frequency of approximately 50 Hz to the 7490 decade counter IC. The frequency of the astable 555 timer is calculated by using the standard formula of the timer.

f = 1.44/(1K + 2*1K)(0.01uF) = 48 Hz.

The output from the 555 timer is then connected to the input of U1 7490 decade counter. When the decade counter reach the count of 9, the outputs of QA and QD will go to logic "1" and the counter is reset. The 7447 BCD to 7 segment decoder is used to drive the 7 segment common anode display.

Parts List

Electronics Hobbies Projects Schematics and Parts List References

2008-12-11T10:06:00.000-08:00

Wiring Color Codes

2008-12-11T09:58:00.000-08:00

Wiring for AC and DC power distribution branch circuits are color coded for identification of individual wires. In some jurisdictions all wire colors are specified in legal documents. In other jurisdictions, only a few conductor colors are so codified. In that case, local custom dictates the “optional” wire colors.

IEC, AC: Most of Europe abides by IEC (International Electrotechnical Commission) wiring color codes for AC branch circuits. These are listed in Table below. The older color codes in the table reflect the previous style which did not account for proper phase rotation. The protective ground wire (listed as green-yellow) is green with yellow stripe.

IEC (most of Europe) AC power circuit wiring color codes.

Function	label	Color, IEC	Color, old IEC
Protective earth	PE	green-yellow	green-yellow
Neutral	N	blue	blue
Line, single phase	L	brown	brown or black
Line, 3-phase	L1	brown	brown or black
Line, 3-phase	L2	black	brown or black
Line, 3-phase	L3	grey	brown or black

UK, AC: The United Kingdom now follows the IEC AC wiring color codes. Table below lists these along with the obsolete domestic color codes. For adding new colored wiring to existing old colored wiring see Cook. [PCk]

UK AC power circuit wiring color codes.

Function	label	Color, IEC	Old UK color
Protective earth	PE	green-yellow	green-yellow
Neutral	N	blue	black
Line, single phase	L	brown	red
Line, 3-phase	L1	brown	red
Line, 3-phase	L2	black	yellow
Line, 3-phase	L3	grey	blue

US, AC:The US National Electrical Code only mandates white (or grey) for the neutral power conductor and bare copper, green, or green with yellow stripe for the protective ground. In principle any other colors except these may be used for the power conductors. The colors adopted as local practice are shown in Table below. Black, red, and blue are used for 208 VAC three-phase; brown, orange and yellow are used for 480 VAC. Conductors larger than #6 AWG are only available in black and are color taped at the ends.

US AC power circuit wiring color codes.

Function	label	Color, common	Color, alternative
Protective ground	PG	bare, green, or green-yellow	green
Neutral	N	white	grey
Line, single phase	L	black or red (2nd hot)
Line, 3-phase	L1	black	brown
Line, 3-phase	L2	red	orange
Line, 3-phase	L3	blue	yellow

Canada: Canadian wiring is governed by the CEC (Canadian Electric Code). See Table below. The protective ground is green or green with yellow stripe. The neutral is white, the hot (live or active) single phase wires are black , and red in the case of a second active. Three-phase lines are red, black, and blue.

Canada AC power circuit wiring color codes.

Function	label	Color, common
Protective ground	PG	green or green-yellow
Neutral	N	white
Line, single phase	L	black or red (2nd hot)
Line, 3-phase	L1	red
Line, 3-phase	L2	black
Line, 3-phase	L3	blue

IEC, DC: DC power installations, for example, solar power and computer data centers, use color coding which follows the AC standards. The IEC color standard for DC power cables is listed in Table below, adapted from Table 2, Cook. [PCk]

IEC DC power circuit wiring color codes.

Function	label	Color
Protective earth	PE	green-yellow
2-wire unearthed DC Power System
Positive	L+	brown
Negative	L-	grey
2-wire earthed DC Power System
Positive (of a negative earthed) circuit	L+	brown
Negative (of a negative earthed) circuit	M	blue
Positive (of a positive earthed) circuit	M	blue
Negative (of a positive earthed) circuit	L-	grey
3-wire earthed DC Power System
Positive	L+	brown
Mid-wire	M	blue
Negative	L-	grey

US DC power: The US National Electrical Code (for both AC and DC) mandates that the grounded neutral conductor of a power system be white or grey. The protective ground must be bare, green or green-yellow striped. Hot (active) wires may be any other colors except these. However, common practice (per local electrical inspectors) is for the first hot (live or active) wire to be black and the second hot to be red. The recommendations in Table below are by Wiles. [JWi] He makes no recommendation for ungrounded power system colors. Usage of the ungrounded system is discouraged for safety. However, red (+) and black (-) follows the coloring of the grounded systems in the table.

US recommended DC power circuit wiring color codes.

Function	label	Color
Protective ground	PG	bare, green, or green-yellow
2-wire ungrounded DC Power System
Positive	L+	no recommendation (red)
Negative	L-	no recommendation (black)
2-wire grounded DC Power System
Positive (of a negative grounded) circuit	L+	red
Negative (of a negative grounded) circuit	N	white
Positive (of a positive grounded) circuit	N	white
Negative (of a positive grounded) circuit	L-	black
3-wire grounded DC Power System
Positive	L+	red
Mid-wire (center tap)	N	white
Negative	L-	black

Resistor Color Codes

2008-12-11T09:57:00.000-08:00

Components and wires are coded are with colors to identify their value and function.

The colors brown, red, green, blue, and violet are used as tolerance codes on 5-band resistors only. All 5-band resistors use a colored tolerance band. The blank (20%) "band" is only used with the "4-band" code (3 colored bands + a blank "band").

Example #1

A resistor colored Yellow-Violet-Orange-Gold would be 47 kΩ with a tolerance of +/- 5%.

Example #2

A resistor colored Green-Red-Gold-Silver would be 5.2 Ω with a tolerance of +/- 10%.

Example #3

A resistor colored White-Violet-Black would be 97 Ω with a tolerance of +/- 20%. When you see only three color bands on a resistor, you know that it is actually a 4-band code with a blank (20%) tolerance band.

Example #4

A resistor colored Orange-Orange-Black-Brown-Violet would be 3.3 kΩ with a tolerance of +/- 0.1%.

Example #5

A resistor colored Brown-Green-Grey-Silver-Red would be 1.58 Ω with a tolerance of +/- 2%.

Example #6

A resistor colored Blue-Brown-Green-Silver-Blue would be 6.15 Ω with a tolerance of +/- 0.25%.

electronics jobs

2008-11-15T21:29:00.000-08:00

Radio-Electronics.Com is developing its new area for electronics, development, software and project management jobs. This new recruitment area will become an invaluable resource for anyone interested in radio jobs, electronics jobs, software jobs, and project management jobs either as a job hunter or as an employer from a recruitment perspective.

Over the next months this recruitment area of this site will develop with more resources for job seekers and employers from around the world, and it will provide a greater number of jobs as a result of new affiliations.

Job Help

Preparing a CV
Getting the best CV

At the interview
Making the most of the job interview

When considering any job moves, or even employment for the first time, it is best to carefully consider the options before applying for a job. The variety of electronics jobs, software jobs and jobs in project management is large and so there is the opportunity to consider the best options.

The first stage in any job application is to consider the best form of career move. Once this has been done and the direction and type of job is known, the CV can be prepared. Take advice on this, and be amenable to alter the CV to get the best option. Once this has been done then it is possible to look at ways of applying for jobs. As in many areas of industry and commence, within the electronics, software and project management arenas there are a number of ways in which opportunities can be found. Many jobs and opportunities are found through one's network of friends and colleagues. It is also possible to look in the newspapers and magazines. There are plenty of electronics, software and project management related magazines available and these can be a good source of information. It is also possible to look at job agencies, and with the internet now providing an up-to-the-minute source this can be an ideal way to find suitable positions.

Contract, consultancy and freelance work

Some help, ideas and suggestions

Freelance or permanent
Whether to opt for a permanent job, or contract / consultancy or freelance approach

Professional indemnity insurance
Whether to take out professional insurance

Overcurrent Protection Circuit

2008-11-15T21:28:00.000-08:00

LTC1154
The LTC1154 single high side gate driver allows using low
cost N-channel FETs for high side switching applications. An
internal charge pump boosts the gate drive voltage above
the positive rail, fully enhancing an N-channel MOS switch
with no external components. Micropower operation, with
8μA standby current and 85μA operating current, allows
use in virtually all systems with maximum effi ciency.
Included on chip is programmable overcurrent sensing.

A time delay can be added to prevent false triggering on
high inrush current loads.

Feature
- Fully Enhances N-Channel Power MOSFETs
- 8μA IQ Standby Current
- 85μA IQ ON Current
- No External Charge Pump Capacitors
- 4.5V to 18V Supply Range
- Short-Circuit Protection
- Thermal Shutdown via PTC Thermistor
- Status Output Indicates Shutdown
- Available in 8-Pin SOIC and PDIP Packages

LTC1154 datasheet pdf

Precision Digital AC Power Controller

2008-09-24T05:48:00.002-07:00

Precision Digital AC Power Controller

SCRs and Triacs are extensively used in modern electronic power controllers—in which power is controlled by means of phase angle variation of the conduction period. Controlling the phase angle can be made simple and easy if we set different firing times corresponding to different firing angles. The design given here is a synchronised programmable timer which achieves this objective.

The following equation for a sinewave shows how firing time and the phase angle are related to each other:
q = 2pft or qµt
Here, q is the angle described by a sinewave in time t (seconds), while f is the frequency of sinewave in Hz. Time period T (in seconds) of a sinewave is equal to the reciprocal of its frequency, i.e. T = 1/f.

The above equation indicates that if one divides the angle described during one complete cycle of the sinewave (2p = 360o) into equal parts, then time period T of the wave will be divided into identical equal parts. Thus, it becomes fairly easy to set the different programmable timings synchronised with the AC mains sinewave at zero crossing. The main advantage of such an arrangement, as already mentioned earlier, is that only the firing time has to be programmed to set different firing angles. It is to be noted that the more precise the timer, the more precise will be the power being controlled.

In this circuit, the time period of mains waveform is divided into 20 equal parts. So, there is a time interval of 1 ms between two consecutive steps. The sampling voltage is unfiltered full-wave and is obtained from the diode bridge at the output of the power transformer. The timer is reset at every zero crossing of full wave and set again instantly for the next delay time. This arrangement helps the timer to be set for every half of mains wave—when the positive half of the mains waveform starts building up, the timer is set for that half and as it begins to cross zero, it gets reset and set again for negative half, when the negative half begins to build up. The process is repeated. Here, instead of using two zero crossing detectors—one for each half of mains wave—a single detector is used to perform both the functions. This is possible because the sampling wave for negative half is inverted by the rectifier diode bridge.

The 18V AC from power transformer is fed to the four diodes in bridge configuration, followed by the filter capacitor which is again followed by a three-terminal voltage regulator IC LM7812. The voltage so obtained drives the circuit. The unfiltered voltage is isolated from the filter capacitor by a diode and is fed to zener diode D8, which acts as a clipper to clip voltage above 6 volts.

This voltage is fed to the base of transistor T1, which is wired as zero crossing detector. When base voltage reaches the threshold, it conducts. It thus supplies a narrow positive pulse which resets the timer at every zero crossing.
A 32.768kHz crystal is used to get stable output of nearly 1 kHz (1,024Hz) frequency after five stages of binary division by an oscillator-cum-divider IC CD4060. The 32.768kHz crystal is used because it can be found in unused quartz clocks and is readily available in the market. But use of a 1kHz crystal using a quad-NAND IC CD4093 as clock generator, as shown in Fig. 2, is better as it provides the exact time interval required. In that case, CD4060 oscillator/divider is not required.

The CD4017B counter-cum-decoder IC then divides this 1kHz signal into ten equal intervals, which are programmed via the single-pole, 10-way rotary switch. Once the delayed output reaches the desired time interval, the corresponding output of CD4017 inhibits the counter CD4017 (via pole of rotary switch and diode D6) and fires the Triac. Transistor T2 here acts as a driver transistor. The reset pin of 4017 is connected to zero crossing detector output to reset it at every zero crossing. (The load-current waveforms for a few positions of the rotary switch, as observed at EFY Lab, are shown in Fig. 3.)
The Circuit can be used as power controller in lighting equipment, hot air oven, universal singal-phase AC motor, heater etc.

Click on the Image for its larger version

Phone Broadcaster

2008-09-24T05:48:00.001-07:00

Phone Broadcaster

Here is a simple yet very useful circuit which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplifier.

One important feature of this circuit is that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies. This not only saves a lot of space but also money. It consumes very low current from telephone lines without disturbing its performance. The circuit is very tiny and can be built using a single-IC type veroboard that can be easily fitted inside a telephone connection box of 3.75 cm x 5 cm.

The circuit consists of two sections, namely, automatic switching section and FM transmitter section.

Automatic switching section comprises resistors R1 to R3, preset VR1, transistors T1 and T2, zener D2, and diode D1. Resistor R1, along with preset VR1, works as a voltage divider. When voltage across the telephone lines is 48V DC, the voltage available at wiper of preset VR1 ranges from 0 to 32V (adjustable). The switching voltage of the circuit depends on zener breakdown voltage (here 24V) and switching voltage of the transistor T1 (0.7V). Thus, if we adjust preset VR1 to get over 24.7 volts, it will cause the zener to breakdown and transistor T1 to conduct. As a result collector of transistor T1 will get pulled towards negative supply, to cut off transistor T2. At this stage, if you lift the handset of the telephone, the line voltage drops to about 11V and transistor T1 is cut off. As a result, transistor T2 gets forward biased through resistor R2, to provide a DC path for transistor T3 used in the following FM transmitter section.

The low-power FM transmitter section comprises oscillator transistor T3, coil L1, and a few other components. Transistor T3 works as a common-emitter RF oscillator, with transistor T2 serving as an electronic ‘on’/‘off’ switch. The audio signal available across the telephone lines automatically modulates oscillator frequency via transistor T2 along with its series biasing resistor R3. The modulated RF signal is fed to the antenna. The telephone conversation can be heard on an FM receiver remotely when it is tuned to FM transmitter frequency.

Lab Note: During testing of the circuit it was observed that the telephone used was giving an engaged tone
when dialed by any subscriber. Addition of resistor R5 and capacitor C6 was found necessary for rectification of the fault.

Click on the Image for its larger version

Telephone Call Meter Using Calculator And COB

2008-09-24T05:47:00.001-07:00

Telephone Call Meter Using Calculator And COB

In this circuit, a simple calculator, in conjunction with a COB (chip-on-board) from an analogue quartz clock, is used to make a telephone call meter. The calculator enables conversion of STD/ISD calls to local call equivalents and always displays current local call-meter reading.

The circuit is simple and presents an elegant look, with feather-touch operation. It consumes very low current and is fully battery operated. The batteries used last more than a year.

Another advantage of using this circuit is that it is compatible with any type of pulse rate format, i.e. pulse rate in whole number, or whole number with decimal value. Recently, the telephone department announced changes in pulse rate format, which included pulse rate in whole number plus decimal value. In such a case, this circuit proves very handy

To convert STD/ISD calls to local calls, this circuit needs accurate 1Hz clock pulses, generated by clock COB. This COB is found inside analogue quartz wall clocks or time-piece mechanisms. It consists of IC, chip capacitors, and crystal that one can retrieve from scrap quartz clock mechanisms. These can be purchased from watch-repairing shops for less than Rs 20

Normally, the COB inside clock mechanism will be in good condition. However, before using the COB, please check its serviceability by applying 1.5V DC across terminals C and D, as shown in the figure. Then check DC voltage across terminals A and B; these terminals in a clock are connected to a coil. If the COB is in good condition, the multimeter needle would deflect forward and backward once every second. In fact, 0.5Hz clock is available at terminals A and B, with a phase difference of 90o. The advantage of using this COB is that it works on a 1.5V DC source

The clock pulses available from terminal A and B are combined using a bridge, comprising diodes D1 to D4, to obtain 1Hz clock pulses. These clock pulses are applied to the base of transistor T1. The collector and emitter of transistor T1 are connected across calculator’s ‘=’ terminals

The number of pulses forming an equivalent call may be determined from the latest telephone directory. However, the pulse rate (PR) found in the directory cannot be used directly in this circuit. For compatibility with this circuit, the pulse rate applicable for a particular place/distance, based on time of the day/holidays, is converted to pulse rate equivalent (PRE) using the formula PRE = 1/PR.

You may prepare a look-up table for various pulse rates and their equivalents (see Table). Suppose you are going to make an STD call in pulse rate 4. Note down from the table the pulse rate equivalent for pulse rate 4, which is 0.25. Please note that on maturity of a call in the telephone exchange, the exchange call meter immediately advances to one call and it will be further incremented according to pulse rate. So one call should always be included before counting the calls.

For making call in pulse rate 4, slide switch S1 to ‘off’ (pulse set position) and press calculator buttons in the following order: 1, ‘+’, 0.25, ‘=’. Here, 1 is initial count, and 0.25 is PRE. Now calculator displays 1.025. This call meter is now ready to count. Now make the call, and as soon as the call matures, immediately slide switch S1 to ‘on’ (start/standby position). The COB starts generating clock pulses of 1 Hz. Transistor T1 conducts once every second, and thus ‘=’ button in calculator is activated electronically once every second. The calculator display
starts from 1.25, advancing every second as follows:
1.25, 1.5, 1.75, 2.00, 2.25, 2.50, and so on.
After finishing the call, immediately slide switch S1 to ‘off’ position (pulse set position) and note down the local call meter reading from the calculator display. If decimal value is more than or equal to 0.9, add another call to the whole number value. If decimal value is less than 0.9, neglect decimal value and note down only whole numbers.

To store this local call meter reading into calculator memory, press ‘M+’ button. Now local call meter reading is stored in memory and is added to the previous local call meter reading. For continuous display of current local call meter reading, press ‘MRC’ button and slide switch S1 to ‘on’ (start/standby position). The current local call meter reading will blink once every second.
In prototype circuit, the author used TAKSUN calculator that costs around Rs 80. The display height was 1 cm. In this calculator, he substituted the two button-type batteries with two externally connected 1.5V R6 type batteries to run the calculator for more than an year.

The power ‘off’ button terminals were made dummy by affixing cellotape on contacts to avoid erasing of memory, should someone accidentally press the power ‘off’ button. This calculator has auto ‘off’ facility. Therefore, some button needs to be pressed frequently to keep the calculator ‘on’. So, in the idle condition, the ‘=’ button is activated electronically once every second by transistor T1, to keep the calculator continuously ‘on’.
Useful hints. Solder the ‘=’ button terminals by drilling small holes in its vicinity on PCB pattern using thin copper wire and solder it neatly, such that the ‘=’ button could get activated electronically as well as manually. Take the copper wire through a hole to the backside of the PCB, from where it is taken out of the calculator as terminals G and H.

At calculator’s battery terminals, solder two wires to ‘+’ and ‘–’ terminals. These wires are also taken out from calculator as terminals E and F. Affix COB on a general-purpose PCB and solder the remaining components neatly. For giving the unit an elegant look, purchase a jewellery plastic box with flip-type cover (size 15cm x 15cm). Now fix the board, calculator, and batteries, along with holder inside the jewellery box. Then mount the box on the wall and paste the look-up table inside the box cover in such a way that on opening the box, it is visible on left side of the box.
Caution. The negative terminals of battery A and battery B are to be kept isolated from each other for proper operation of this circuit.

LookUp Table
Pulse rate (PR)	2	2.5	3	4	6	8	12	16	24	32	36	48
Pulse rate eqlt.	0.5000	0.4000	0.333	0.250	0.166	0.125	0.083	0.062	0.041	0.031	0.027	0.020
Note : Here PRE is shown up to three decimal places. In practice, one may use up to five or six decimal places.

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Telephone Conversation Recorder

2008-09-24T05:46:00.000-07:00

Telephone Conversation Recorder

This circuit enables automatic switching-on of the tape recorder when the handset is lifted. The tape recorder gets switched off when the handset is replaced. The signals are suitably attenuated to a level at which they can be recorded using the ‘MIC-IN’ socket of the tape recorder.

Points X and Y in the circuit are connected to the telephone lines. Resistors R1 and R2 act as a voltage divider. The voltage appearing across R2 is fed to the ‘MIC-IN’ socket of the tape recorder. The values of R1 and R2 may be changed depending on the input impedance of the tape recorder’s ‘MIC-IN’ terminals. Capacitor C1 is used for blocking the flow of DC.

The second part of the circuit controls relay RL1, which is used to switch on/off the tape recorder. A voltage of 48 volts appears across the telephone lines in on-hook condition. This voltage drops to about 9 volts when the handset is lifted. Diodes D1 through D4 constitute a bridge rectifier/polarity guard. This ensures that transistor T1 gets voltage of proper polarity, irrespective of the polarity of the telephone lines.

During on-hook condition, the output from the bridge (48V DC) passes through 12V zener D5 and is applied to the base of transistor T1 via the voltage divider comprising resistors R3 and R4. This switches on transistor T1 and its collector is pulled low. This, in turn, causes transistor T2 to cut off and relay RL1 is not energised.

When the telephone handset is lifted, the voltage across points X and Y falls below 12 volts and so zenor diode D5 does not conduct. As a result, base of transistor T1 is pulled to ground potential via resistor R4 and thus is cut off. Thus, base of transistor T2 gets forward biased via resistor R5, which results in the energisation of relay RL1. The tape recorder is switched ‘on’ and recording begins.

The tape recorder should be kept loaded with a cassette and the record button of the tape recorder should remain pressed to enable it to record the conversation as soon as the handset is lifted. Capacitor C2 ensures that the relay is not switched on-and-off repeatedly when a number is being dialled in pulse dialing mode.

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Protection for your Electrical Appliances

2008-09-24T05:45:00.001-07:00

Protection for your Electrical Appliances

Here is a very low-cost circuit to save your electrically operated appliances, such as tv, tape recorder, refrigerator, and other instruments during sudden tripping and resumption of mains supply. Appliances like refrigerators and air-conditioners are more prone to damage due to such conditions.

The simple circuit given here switches off the mains supply to the load as soon as the power trips. The supply can be resumed only by manual intervention. Thus, the supply may be switched on only after it has stabilised.

The circuit comprises a step-down transformer followed by a full-wave rectifier and smoothing capacitor C1 which acts as a supply source for relay rl1. Initially, when the circuit is switched on, the power supply path to the step-down transformer X1 as well as the load is incomplete, as the relay is in de-energised state. To energise the relay, press switch S1 for a short duration. This completes the path for the supply to transformer X1 as also the load via closed contacts of switch S1. Meanwhile, the supply to relay becomes available and it gets energised to provide a parallel path for the supply to the transformer as well as the load.

If there is any interruption in the power supply, the supply to the transformer is not available and the relay de-energises. Thus, once the supply is interrupted even for a brief period, the relay is de-energised and you have to press switch S1 momentarily (when the supply resumes) to make it available to the load.

Very-short-duration (say, 1 to 5 milliseconds) interruptions or fluctuations will not affect the circuit because of presence of large-value capacitor which has to discharge via the relay coil. Thus the circuit provides suitable safety against erratic power supply conditions.

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Simple Code Lock

2008-09-24T05:44:00.000-07:00

Simple Code Lock

The circuit described here is of an electronic combination lock for daily use. It responds only to the right sequence of four digits that are keyed in remotely. If a wrong key is touched, it resets the lock. The lock code can be set by connecting the line wires to the pads a, b, c, and d in the figure. For example, if the code is 1756, connect line 1 to a, line 7 to b, line 5 to c, line 6 to d and rest of the lines—2, 3, 4, 8, and 9—to the reset pad as shown by dotted lines in the figure.

The circuit is built around two cd4013 dual-d flip-flop ics. The clock pins of the four flip-flops are connected to a, b, c, and d pads. The correct code sequence for energisation of relay rl1 is realised by clocking points a, b, c, and d in that order. The five remaining switches are connected to reset pad which resets all the flip-flops. Touching the key pad switch a/b/c/d briefly pulls the clock input pin high and the state of flip-flop is altered. The q output pin of each flip-flop is wired to d input pin of the next flip-flop while d pin of the first flip-flop is grounded. Thus, if correct clocking sequence is followed then low level appears at q2 output of ic2 which energises the relay through relay driver transistor t1. The reset keys are wired to set pins 6 and 8 of each ic. (Power-on-reset capacitor c1 has been added at efy during testing as the state of q output is indeterminate during switching on operation.)

This circuit can be usefully employed in cars so that the car can start only when the correct code sequence is keyed in via the key pad. The circuit can also be used in various other applications.

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Long-range FM Transmitter

2008-09-24T05:43:00.002-07:00

Long-range FM Transmitter

Several circuits for constructing FM transmitters have been published in EFY. The power output of most of these circuits are very low because no power amplifier stages were incorporated.

The transmitter circuit described here has an extra RF power amplifier stage, after the oscillator stage, to raise the power output to 200-250 milliwatts. With a good matching 50-ohm ground plane antenna or multi-element Yagi antenna, this transmitter can provide reasonably good signal strength up to a distance of about 2 kilometres.

The circuit built around transistor T1 (BF494) is a basic low-power variable-frequency VHF oscillator. A varicap diode circuit is included to change the frequency of the transmitter and to provide frequency modulation by audio signals. The output of the oscillator is about 50 milliwatts. Transistor T2 (2N3866) forms a VHF-class A power amplifier. It boosts the oscillator signals’ power four to five times. Thus, 200-250 milliwatts of power is generated at the collector of transistor T2.

For better results, assemble the circuit on a good-quality glass epoxy board and house the transmitter inside an aluminium case. Shield the oscillator stage using an aluminium sheet.
Coil winding details are given below:
L1 - 4 turns of 20 SWG wire close wound over 8mm diameter plastic former.
L2 - 2 turns of 24 SWG wire near top end of L1.
(Note: No core (i.e. air core) is used for the above coils)
L3 - 7 turns of 24 SWG wire close wound with 4mm diameter air core.
L4 - 7 turns of 24 SWG wire-wound on a ferrite bead (as choke)

Potentiometer VR1 is used to vary the fundamental frequency whereas potentiometer VR2 is used as power control. For hum-free operation, operate the transmitter on a 12V rechargeable battery pack of 10 x 1.2-volt Ni-Cd cells. Transistor T2 must be mounted on a heat sink. Do not switch on the transmitter without a matching antenna. Adjust both trimmers (VC1 and VC2) for maximum transmission power. Adjust potentiometer VR1 to set the fundamental frequency near 100 MHz.

This transmitter should only be used for educational purposes. Regular transmission using such a transmitter without a licence is illegal in India.

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Long-range FM Transmitter

2008-09-24T05:43:00.001-07:00

Long-range FM Transmitter

Several circuits for constructing FM transmitters have been published in EFY. The power output of most of these circuits are very low because no power amplifier stages were incorporated.

This transmitter should only be used for educational purposes. Regular transmission using such a transmitter without a licence is illegal in India.

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Self-switching Power Supply

2008-09-24T05:42:00.000-07:00

Self-switching Power Supply

One of the main features of the regulated power supply circuit being presented is that though fixed-voltage regulator LM7805 is used in the circuit, its output voltage is variable. This is achieved by connecting a potentiometer between common terminal of regulator IC and ground. For every 100-ohm increment in the in-circuit value of the resistance of potentiometer VR1, the output voltage increases by 1 volt. Thus, the output varies from 3.7V to 8.7V (taking into account 1.3-volt drop across diodes D1 and D2).

Another important feature of the supply is that it switches itself off when no load is connected across its output terminals. This is achieved with the help of transistors T1 and T2, diodes D1 and D2, and capacitor C2. When a load is connected at the output, potential drop across diodes D1 and D2 (approximately 1.3V) is sufficient for transistors T2 and T1 to conduct. As a result, the relay gets energised and remains in that state as long as the load remains connected. At the same time, capacitor C2 gets charged to around 7-8 volt potential through transistor T2. But when the load is disconnected, transistor T2 is cut off. However, capacitor C2 is still charged and it starts discharging through base of transistor T1. After some time (which is basically determined by value of C2), relay RL1 is de-energised, which switches off the mains input to primary of transformer X1. To resume the power again, switch S1 should be pressed momentarily. Higher the value of capacitor C2, more will be the delay in switching off the power supply on disconnection of the load, and vice versa.

Though in the prototype a transformer with a secondary voltage of 12V-0V, 250mA was used, it can nevertheless be changed as per user’s requirement (up to 30V maximum. and 1-ampere current rating). For drawing more than 300mA current, the regulator IC must be fitted with a small heat sink over a mica insulator. When the transformer’s secondary voltage increases beyond 12 volts (RMS), potentiometer VR1 must be redimensioned. Also, the relay voltage rating should be redetermined.

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Electrical Equipment Control UsingPC

2008-09-24T05:41:00.000-07:00

Electrical Equipment Control UsingPC: by P.V Vinod Kumar

Here is a novel idea for using the printer port of a PC, for con-trol application using software and some interface hardware. The interface circuit along with the given software can be used with the printer port of any PC for controlling up to eight equipment.

The interface circuit shown in the figure is drawn for only one device, being controlled by D0 bit at pin 2 of the 25-pin parallel port. Identical circuits for the remaining data bits D1 through D7 (available at pins 3 through 9) have to be similarly wired. The use of opto-coupler ensures complete isolation of the PC from the relay driver circuitry.

When the program is loaded and run, the monitor will show the control panel-with the control bar at the extreme left. The bar can be moved using the right and left arrow keys. Switching on/off of bits D0-D7 is done by bringing the bar over the appropriate square and then pressing the ‘Q’ key for ON and ‘W’ key for OFF operation. The monitor will show the status of the relevant switch by indicating ‘1’ for ON and ‘0’ for OFF status of the switch. In addition, the current date and time is also displayed on the screen.

Program Listing in Basic

CLS : SCREEN 2
KEY(1) ON: ON KEY(1) GOSUB FINIS
KEY(5) ON: ON KEY(5) GOSUB RETIRE
KEY(10) ON: ON KEY(10) GOSUB ALLON
PORT% = &H378
OUT PORT%, 0
LOCATE 8, 10: PRINT "<--- --->"
V$ = STRING$(27, "²")
LOCATE 5, 6: PRINT V$; SPC(1); "CONTROL PANEL"; SPC(2); V$
LINE (40, 31)-(600, 180), 1, B
LINE (40, 40)-(600, 180), 1, B
LINE (40, 100)-(600, 120), 1, BF
LINE (140, 40)-(460, 110), 1, B
LOCATE 8, 65: PRINT "ON-----Q"
LOCATE 12, 65: PRINT "OFF----W"
LOCATE 19, 15: PRINT "F1"; SPC(24); "F5"; SPC(27); "F10"
LOCATE 21, 10: PRINT "EMERGENCY OFF"; SPC(16); "LOGOUT"; SPC(24); "ALLON"
D$ = DATE$
J$ = MID$(D$, 1, 3)
K$ = MID$(D$, 4, 3)
L$ = MID$(D$, 9, 2) LOCATE 5, 7: PRINT SPC(1); K$; J$; L$; SPC(1); ""
STAT:
PSET (145, 85): DRAW "R20U10L20D10"
PSET (185, 85): DRAW "R20U10L20D10"
PSET (225, 85): DRAW "R20U10L20D10"
PSET (265, 85): DRAW "R20U10L20D10"
PSET (305, 85): DRAW "R20U10L20D10"
PSET (345, 85): DRAW "R20U10L20D10"
PSET (385, 85): DRAW "R20U10L20D10"
PSET (425, 85): DRAW "R20U10L20D10"
T$ = TIME$
Y$ = MID$(T$, 1, 2)
Y = VAL(Y$)
IF Y < 12 THEN PP$ = "AM" ELSE PP$ = "PM"
IF Y > 12 THEN Y = Y - 12
U$ = MID$(T$, 3, 3)
LOCATE 5, 64: PRINT SPC(1); Y; U$; PP$; SPC(1); ""
LOCATE 9, 20: PRINT "1"; SPC(4); "2"; SPC(4); "3"; SPC(4); "4"; SPC(4); "5"; SPC(4); "6"; SPC(4); "7"; SPC(4); "8"
LOCATE 12, 19: PRINT AA; SPC(2); SS; SPC(2); DD; SPC(2); FF; SPC(2); GG; SPC(1); SPC(1); HH;
SPC(2); JJ; SPC(2); KK
X$ = INKEY$
X$ = RIGHT$(X$, 1)
N = INP(PORT%)
IF X$ = "K" THEN J = J - 40
IF X$ = "M" THEN J = J + 40
PSET (J + 105, 85): DRAW
"R20U10L20D10R2U10R2D10R2U10R2D10R2U10R2D10R2U10R2D10R2U10R2D10"
FOR T = 1 TO 400: NEXT
PRESET (J + 105, 85): DRAW
"R20U10L20D10R2U10R2D10R2U10R2D10R2U10R2D10R2U10R2D10R2U10R2D10"
IF J + 105 < 105 THEN J = 0
IF J >= 360 THEN J = 360
IF (J = 40) AND (X$ = "Q" OR X$ = "q") THEN GOSUB APPLE
IF (J = 40) AND (X$ = "W" OR X$ = "w") THEN GOSUB APPLEOF
IF (J = 80) AND (X$ = "Q" OR X$ = "q") THEN GOSUB BAT
IF (J = 80) AND (X$ = "W" OR X$ = "w") THEN GOSUB BATOF
IF (J = 120) AND (X$ = "Q" OR X$ = "q") THEN GOSUB TALE
IF (J = 120) AND (X$ = "W" OR X$ = "w") THEN GOSUB TALEOF
IF (J = 160) AND (X$ = "Q" OR X$ = "q") THEN GOSUB FLAT
IF (J = 160) AND (X$ = "W" OR X$ = "w") THEN GOSUB FLATOF
IF (J = 200) AND (X$ = "Q" OR X$ = "q") THEN GOSUB FAT
IF (J = 200) AND (X$ = "W" OR X$ = "w") THEN GOSUB FATOF
IF (J = 240) AND (X$ = "Q" OR X$ = "q") THEN GOSUB SILK
IF (J = 240) AND (X$ = "W" OR X$ = "w") THEN GOSUB SILKOF
IF (J = 280) AND (X$ = "Q" OR X$ = "q") THEN GOSUB SEVEN
IF (J = 280) AND (X$ = "W" OR X$ = "w") THEN GOSUB SEVENOF
IF (J = 320) AND (X$ = "Q" OR X$ = "q") THEN GOSUB LAST
IF (J = 320) AND (X$ = "W" OR X$ = "w") THEN GOSUB LASTOF
GOTO STAT '------------ALL THE SUBROUTINES ARE BELOW--------------
APPLE: SOUND 500, 2
AA = 1
LOCATE 6, 50
Q = 1 OR N
OUT PORT%, Q
RETURN
BAT: SOUND 500, 2
SS = 1
W = 2 OR N
OUT PORT%, W
RETURN
TALE: SOUND 500, 2
DD = 1
Q = 4 OR N
OUT PORT%, Q
RETURN
FLAT: SOUND 500, 2
FF = 1
Q = 8 OR N
OUT PORT%, Q
RETURN
FAT: SOUND 500, 2
GG = 1
Q = 16 OR N
OUT PORT%, Q
RETURN
SILK: SOUND 500, 2
HH = 1
Q = 32 OR N
OUT PORT%, Q
RETURN
SEVEN: SOUND 500, 2
JJ = 1
Q = 64 OR N
OUT PORT%, Q
RETURN
LAST: SOUND 500, 2
KK = 1
Q = 128 OR N
OUT PORT%, Q
RETURN
TALEOF: SOUND 400, 1
IF DD = 0 THEN RETURN
DD = 0
IF N = 4 THEN P = 0
IF N < 4 THEN P = N
IF N > 4 THEN P = N - 4
OUT PORT%, P RETURN
APPLEOF: SOUND 400, 1
IF AA = 0 THEN RETURN
AA = 0
IF N = 1 THEN I = 0
IF N > 1 THEN I = N - 1
OUT PORT%, I
RETURN BATOF: SOUND 400, 1
IF SS = 0 THEN RETURN
SS = 0
IF N = 2 THEN U = 0
IF N > 2 THEN U = N - 2
IF N < 2 THEN U = N
OUT PORT%, U RETURN
FLATOF: SOUND 400, 1
IF FF = 0 THEN RETURN FF = 0
IF N = 8 THEN E = 0
IF N < 8 THEN E = N
IF N > 8 THEN E = N - 8
OUT PORT%, E
RETURN
FATOF: SOUND 400, 1
IF GG = 0 THEN RETURN
GG = 0
IF N = 16 THEN Y = 0
IF N < 16 THEN Y = N
IF N > 16 THEN Y = N - 16
OUT PORT%, Y
RETURN
SILKOF: SOUND 400, 1
IF HH = 0 THEN RETURN
HH = 0 IF N = 32 THEN Y = 0
IF N < 32 THEN Y = N
IF N > 32 THEN Y = N - 32
OUT PORT%, Y
RETURN
SEVENOF: SOUND 400, 1
IF JJ = 0 THEN RETURN
JJ = 0
IF N = 64 THEN U = 0
IF N < 64 THEN U = N
IF N > 64 THEN U = N - 64
OUT PORT%, U
RETURN
LASTOF: SOUND 400, 1
IF KK = 0 THEN RETURN
KK = 0
IF N = 128 THEN Z = 0
IF N < 128 THEN Z = N
IF N > 128 THEN Z = N - 128
OUT PORT%, Z
RETURN
ALLON: SOUND 500, 4
OUT PORT%, 255
AA = 1: SS = 1: DD = 1: FF = 1: GG = 1: HH = 1: JJ = 1: KK = 1
RETURN
FINIS: SOUND 400, 2
OUT PORT%, 0
AA = 0: SS = 0: DD = 0: FF = 0: GG = 0: HH = 0: JJ = 0: KK = 0
RETURN
RETIRE:
OUT PORT%, 0
END

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Teleremote Control

2008-09-24T05:40:00.002-07:00

Teleremote Control

Here is a teleremote circuit which enables switching ‘on’ and ‘off’ of appliances through telephone lines. It can be used to switch appliances from any distance, overcoming the limited range of infrared and radio remote controls

The circuit described here can be used to switch up to nine appliances (corresponding to the digits 1 through 9 of the telephone key-pad). The DTMF signals on telephone instrument are used as control signals. The digit ‘0’ in DTMF mode is used to toggle between the appliance mode and normal telephone operation mode. Thus the telephone can be used to switch on or switch off the appliances also while being used for normal conversation.

The circuit uses IC KT3170 (DTMF-to-BCD converter), 74154 (4-to-16-line demult-iplexer), and five CD4013 (D flip-flop) ICs. The working of the circuit is as follows.

Once a call is established (after hearing ring-back tone), dial ‘0’ in DTMF mode. IC1 decodes this as ‘1010,’ which is further demultiplexed by IC2 as output O10 (at pin 11) of IC2 (74154). The active low output of IC2, after inversion by an inverter gate of IC3 (CD4049), becomes logic 1. This is used to toggle flip-flop-1 (F/F-1) and relay RL1 is energised. Relay RL1 has two changeover contacts, RL1(a) and RL1(b). The energised RL1(a) contacts provide a 220-ohm loop across the telephone line while RL1(b) contacts inject a 10kHz tone on the line, which indicates to the caller that appliance mode has been selected. The 220-ohm loop on telephone line disconnects the ringer from the telephone line in the exchange. The line is now connected for appliance mode of operation.

If digit ‘0’ is not dialed (in DTMF) after establishing the call, the ring continues and the telephone can be used for normal conversation. After selection of the appliance mode of operation, if digit ‘1’ is dialed, it is decoded by IC1 and its output is ‘0001’. This BCD code is then demultiplexed by 4-to-16-line demultiplexer IC2 whose corresponding output, after inversion by a CD4049 inverter gate, goes to logic 1 state. This pulse toggles the corresponding flip-flop to alternate state. The flip-flop output is used to drive a relay (RL2) which can switch on or switch off the appliance connected through its contacts. By dialing other digits in a similar way, other appliances can also be switched ‘on’ or ‘off.’

Once the switching operation is over, the 220-ohm loop resistance and 10kHz tone needs to be removed from the telephone line. To achieve this, digit ‘0’ (in DTMF mode) is dialed again to toggle flip-flop-1 to de-energise relay RL1, which terminates the loop on line and the 10kHz tone is also disconnected. The telephone line is thus again set free to receive normal calls.

This circuit is to be connected in parallel to the telephone instrument.

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Low-cost Transistorised Intercom

2008-09-24T05:40:00.001-07:00

Low-cost Transistorised Intercom

Several intercom circuits have ap-peared in EFY using integrated circuits. The circuit described here uses three easily available transistors only. Even a beginner can easily assemble it on a piece of veroboard.

The circuit comprises a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pressed, the amplifier circuit formed around transistors T1 and T2 gets converted into an asymmetrical astable multivib-rator generating ring signals. These ring signals are amplified by transistor T3 to drive the speaker of earpiece.

Current consumption of this intercom is 10 to 15 mA only. Thus a 9-volt PP3 battery would have a long life, when used in this circuit.

For making a two-way intercom, two identical units, as shown in figure, are required to be used. Output of one amplifier unit goes to speaker of the other unit, and vice versa. For single-battery operation, join corresponding supply and ground terminals of both the units together.

The complete circuit, along with microphone and earpiece etc, can be housed inside the plastic body of a cellphone toy, which is easily available in the market. Suggested cellphone cabinet is shown.

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Cordless Phone Backup

2008-09-24T05:39:00.002-07:00

Cordless Phone Backup

Normally the base of a cordless phone has an adaptor and the handset has Ni-Cd cells for its operation. The base unit becomes inoperative in case of power failure. In such conditions, it is better to provide a backup using Ni-Cd cells externally. Here is a simple circuit which can be used with cordless phone SANYO CLT-420 or similar sets.

The working is simple. When AC mains is present, Ni-Cd cells are charged through IC LM317L, which is wired as a current source. Also, diode D3 is reverse-biased, which keeps Ni-Cd cells isolated from positive rail. When AC mains goes off, the Ni-Cd cells provide supply to the cordless phone base unit through diode D3. A green LED is used to indicate the presence of AC mains.

Each Ni-Cd cell costs around Rs 34, and the cost of the backup unit, including the box and cells, would not exceed Rs 300. Hence the circuit is well worth the investment.

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Sleep-switch cum Wake-up Timer

2008-09-24T05:39:00.001-07:00

Sleep-switch cum Wake-up Timer

Here is a sleep-switch circuit that can be easily converted into a wake-up timer. A dual-mode time setting makes the system versatile. The circuit is low-cost and can function as a precise timer.

The heartbeat produced by IC1 is a sharp 1Hz square wave signal having a duty cycle of 50 per cent. This is achieved by using a 4.194304MHz crystal in combination with discrete components around it. The 1Hz output of IC1 is connected to IC2 as well as one of the terminals of switch S1. IC2 is configured as divide-by-6 counter while IC3 further divides the output of IC2 by ten to produce one-minute output at its pin 12. This is brought to the second terminal of two-way switch S1 to help select either the ‘minutes’ or the ‘seconds’ mode of operation for IC4.

The decade counter IC4 provides binary output as it counts up the input pulses and IC5 decodes/converts them to 1-of-10 outputs (units). Similarly, the IC6-IC7 pair provides tens output since IC6 clock input pin is connected to D output pin of IC4.

Rotary switches S2 and S3 can be set to select any time between either 0 to 99 seconds or 0 to 99 minutes, depending upon the position of mode switch S1. Switches S2 and S3 could also be replaced by thumb-wheel type switches or 10-position DIP switches with one of their side terminals shorted together to serve as a pole. Please note that IC5 and IC7 (74145) have active low outputs.

The outputs from switches S2 and S3 are input to a two-input OR gate inside IC8 (7432) to obtain active low output on completion of the set time delay to deactivate relay RL1 through relay driver transistor T1 (normally conducting) when set time is reached. When transistor T1 cuts off, its collector goes high to reset oscillator IC1, and thus count at output of IC4 and IC6 gets locked. For resetting or restarting, the power supply to the circuit should be switched off and then switched on again.

The BCD outputs of IC4 and IC6 are converted to seven-segment outputs by IC9 and IC10 to drive the units and tens displays respectively for indicating elapsed time continuously. The relay contacts (normally open and normally closed) can be suitably used to energise or de-energise an alarm after the preset delay. It can thus be used as wake-up alarm or sleep timer.

If you want to de-energise the relay, say after 30 minutes, then set switch S1 to minutes mode, S2 to 0 and S3 to 3, and then switch on the supply to the circuit. After 30 minutes the outputs at poles of switches S2 and S3 will go low and so also the output of OR gate (IC8). As a result, transistor T1 will be cut-off to de-energise the relay.

One can easily add 0-99 hours capability by cascading two counters as shown in the minutes counter section comprising IC2 and IC3. Input clock for hours counter would be the minutes clock available at pin 12 of IC3.

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Simple Analog-to-digital Converter

2008-09-24T05:38:00.002-07:00

Simple Analog-to-digital Converter

Normally analogue-to-digital con-verter (ADC) needs interfacing through a microprocessor to convert analogue data into digital format. This requires hardware and necessary software, resulting in increased complexity and hence the total cost.

The circuit of A-to-D converter shown here is configured around ADC 0808, avoiding the use of a microprocessor. The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding A, B and C address lines.

Usually the control signals EOC (end of conversion), SC (start conversion), ALE (address latch enable) and OE (output enable) are interfaced by means of a microprocessor. However, the circuit shown here is built to operate in its continuous mode without using any microprocessor. Therefore the input control signals ALE and OE, being active-high, are tied to Vcc (+5 volts). The input control signal SC, being active-low, initiates start of conversion at falling edge of the pulse, whereas the output signal EOC becomes high after completion of digitisation. This EOC output is coupled to SC input, where falling edge of EOC output acts as SC input to direct the ADC to start the conversion.

As the conversion starts, EOC signal goes high. At next clock pulse EOC output again goes low, and hence SC is enabled to start the next conversion. Thus, it provides continuous 8-bit digital output corresponding to instantaneous value of analogue input. The maximum level of analogue input voltage should be appropriately scaled down below positive reference (+5V) level.

The ADC 0808 IC requires clock signal of typically 550 kHz, which can be easily derived from an astable multivibrator constructed using 7404 inverter gates. In order to visualise the digital output, the row of eight LEDs (LED1 through LED8) have been used, wherein each LED is connected to respective data lines D0 through D7. Since ADC works in the continuous mode, it displays digital output as soon as analogue input is applied. The decimal equivalent digital output value D for a given analogue input voltage Vin can be calculated from the relationship

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Magnetic Proximity Switch

2008-09-24T05:38:00.001-07:00

Magnetic Proximity Switch

There is practically no house without an overhead tank (OHT). People who use electrically-operated water pumps for filling the OHT find it very inconvenient to switch off the pump when their overhead tank starts overflowing, specially when they are busy. So there is plenty of water wastage as well as wastage of power (consumed by the pump). However, there is a solution to get rid of this headache. The circuit given here will switch off the pump and also generate a melodious tune when the overhead tank gets filled up to the maximum desired level. All you have to do is switch off the power supply to the circuit when you are relatively free. The heart of the circuit is the CMOS latch CD4001. Usually the latch can be operated in two modes, namely, set and reset mode, i.e. the latch output can be set to logic 1 or reset to logic 0 by applying appropriate active low level input signal to pins 1 and 13, respectively. Here, in the given circuit, the set point is pin 1 and the reset point is pin 13. The inverted output of the latches are obtained at pins 3 and 11, respectively. When the circuit is powered there is a voltage drop at pin 1 due to the resistor-capacitor R1-C1 combination. The values of resistor R1 and C1 are chosen in such a way that pin 1 is low for about two seconds which is sufficient to energise the relay through transistor T1 and thus the pump starts running. When sufficient water gets filled in the overhead tank, switch S1 in the sensing unit, in the overhead tank as shown in Fig. 2, sends an active low signal to pin 13 which resets latch gate N1 output to logic 0. This causes transistor T1 to stop conducting, thereby de-energising the relay and shutting down the pump. At the same time, the output at pin 11 of gate N2 will be logic 1. This results in conduction of transistor T2 and melodious buzzer sounds. The green LED also lights up while the red LED, which remains on as long as the relay remains energised, gets switched off when water reaches the specified level in the overhead tank. The circuit possesses the following advantages:

Special sensing mechanism (easy to build) is used to sense the water level in the overhead tank.
One can replace CD4011 with IC 7400. In that case, a 5.1V zener may be connected additionally between pin 14 of IC1 and the ground.
The circuit can be easily fabricated on a general-purpose PCB.

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Ultra Low Drop Linar Regulator

2008-09-24T05:36:00.004-07:00

Ultra Low Drop Linar Regulator

e circuit is a MOSFET based linear voltage regulator with a voltage drop of as low as 60 mV at 1 ampere. Drop of a fewer millivolts is possible with better MOSFETs having lower RDS(on) resistance. The circuit in Fig. 1 uses 15V-0-15V secondary from a step-down transformer and employs an n-channel MOSFET IRF 540 to get the regulated 12V output from DC input, which could be as low as 12.06V. The gate drive voltage required for the MOSFET is generated using a voltage doubler circuit consisting of diodes D1 and D2 and capacitors C1 and C4. To turn the MOSFET fully on, the gate terminal should be around 10V above the source terminal which is connected to the output here. The voltage doubler feeds this voltage to the gate through resistor R1. Adjustable shunt regulator TL431 (IC2) is used here as an error amplifier, and it dynamically adjusts the gate voltage to maintain the regulation at the output. With adequate heatsink for the MOSFET, the circuit can provide up to 3A output at slightly elevated minimum voltage drop. Trimpot VR1 in the circuit is used for fine adjustment of the output voltage. Combination of capacitor C5 and resistor R2 provides error-amplifier compensation. The circuit is provided with a short-circuit crow-bar protection to guard the components against over-stress during accidental short at the output. This crow-bar protection will work as follows: Under normal working conditions, the voltage across capacitor C3 will be 6.3V and diode D5 will be in the off state since it will be reverse-biased with the output voltage of 12V. However, during output short-circuit condition, the output will momentarily drop, causing D5 to conduct and the opto-triac MOC3011 (IC1) will get triggered, pulling down the gate voltage to ground, and thus limiting the output current. The circuit will remain latched in this state, and input voltage has to be switched off to reset the circuit. The circuit shown in Fig. 2 follows a similar scheme. It can be utilised when the regulator has to work from a DC rail in place of 15V-0-15V AC supply. The gate voltage here is generated using an LM555 charge pump circuit as follows: When 555 output is low, capacitor C2 will get charged through diode D1 to the input voltage. In the next half cycle, when the 555 output goes high, capacitor C3 will get charged to almost double the input voltage. The rest of the circuit works in a similar fashion as the circuit of Fig. 1. These circuits above will help reduce power-loss by allowing to keep lower input voltage range to the regulator during initial design or even in existing circuits. This will keep the output regulated with relatively low input voltage compared to the conventional regulators. The minimum voltage drop can be further reduced using low RDS(on) MOSFETs or by paralleling them.

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