20 CIRCUITS as of  28-2-2009

                       

                                                               See TALKING ELECTRONICS WEBSITE

                                           email Colin Mitchell:   talking@tpg.com.au
 

INTRODUCTION
This is the second half of our Transistor Circuits e-book. It contains a further 100 circuits, with many of them containing one or more Integrated Circuits (ICs).
It's amazing what you can do with transistors but when Integrated Circuits came along, the whole field of electronics exploded.
IC's can handle both analogue as well as digital signals but before their arrival, nearly all circuits were analogue or very simple "digital" switching circuits.
Let's explain what we mean.
The word analogue is a waveform or signal that is changing (increasing and decreasing) at a constant or non constant rate. Examples are voice, music, tones, sounds and frequencies. Equipment such as radios, TV's and amplifiers process analogue signals.
Then digital came along.
Digital is similar to a switch turning something on and off.
The advantage of digital is twofold.
Firstly it is a very reliable and accurate way to send a signal. The signal is either HIGH or LOW  (On or OFF). It cannot be half-on or one quarter off.
And secondly, a circuit that is ON, consumes the least amount of energy in the controlling device. In other words, a transistor that is fully turned ON and driving a motor, dissipates the least amount of heat. If it is slightly turned ON or nearly fully turned ON, it gets very hot.
And obviously a transistor that is not turned on at all will consume no energy.
A transistor that turns ON fully and OFF fully is called a SWITCH.
When two transistors are cross-coupled in the form of a flip flop, any pulses entering the circuit cause it to flip and flop and the output goes HIGH on every second pulse. This means the circuit halves the input pulses and is the basis of counting or dividing.
Digital circuits also introduce the concept of two inputs creating a HIGH output when both are HIGH and variations of this.
This is called "logic" and introduces terms such as "Boolean algebra" and "gates."
Integrated Circuits started with a few transistors in each "chip" and increased to whole mini or micro computers in a single chip. These chips are called Microcontrollers and a single chip with a few surrounding components can be programmed to play games, monitor heart-rate and do all sorts of amazing things. Because they can process information at high speed, the end result can appear to have intelligence and this is where we are heading: AI (Artificial Intelligence).

But let's crawl before we walk and come to understand how to interface some of these chips to external components.
In this Transistor Circuits ebook, we have presented about 100 interesting circuits using transistors and chips.
In most cases the IC will contain 10 - 100 transistors, cost less than the individual components and take up much less board-space. They also save a lot of circuit designing and quite often consume less current than discrete components.
In all, they are a fantastic way to get something working with the least componentry.
A list of of Integrated Circuits (Chips) is provided at the end of this book to help you identify the pins and show you what is inside the chip.
Some of the circuits are available from Talking Electronics as a kit, but others will have to be purchased as individual components from your local electronics store. Electronics is such an enormous field that we cannot provide kits for everything. But if you have a query about one of the circuits, you can contact me.

Colin Mitchell
TALKING ELECTRONICS.
talking@tpg.com.au

To save space we have not provided lengthy explanations of how the circuits work. This has already been covered in TALKING ELECTRONICS Basic Electronics Course, and can be obtained on a CD for $10.00 (posted to anywhere in the world) See Talking Electronics website for more details:  http://www.talkingelectronics.com

 

MORE INTRO
There are two ways to learn electronics.
One is to go to school and study theory for 4 years and come out with all the theoretical knowledge in the world but almost no practical experience.
We know this type of person. We employed them (for a few weeks!). They think everything they design WILL WORK because their university professor said so.
The other way is to build circuit after circuit and get things to work. You may not know the in-depth theory of how it works but trial and error gets you there.
We know. We employed this type of person for up to 12 years.
I am not saying one is better than the other but most electronics enthusiasts are not "book worms" and anyone can succeed in this field by constantly applying themselves to constructing projects. You actually learn 10 times faster by applying yourself and we have had technicians repairing equipment after only a few weeks on the job.
It would be nothing for an enthusiast to build 30 - 40 circuits from our previous Transistor eBook and a similar number from this book. Many of the circuits are completely different to each other and all have a building block or two that you can learn from.
Electronics enthusiasts have an uncanny understanding of how a circuit works and if you have this ability, don't let it go to waste.
Electronics will provide you a comfortable living for the rest of your life and I mean this quite seriously. The market is very  narrow but new designs are coming along all the time and new devices are constantly being invented and more are always needed.
Once you get past this eBook of "Chips and Transistors" you will want to investigate microcontrollers and this is when your options will explode.
You will be able to carry out tasks you never thought possible, with a chip as small as 8 pins and a few hundred lines of code.
As I say in my speeches. What is the difference between a "transistor man" and a "programmer?"  TWO WEEKS!
In two weeks you can start to understand the programming code for a microcontroller and perform simple tasks such as flashing a LED and produce sounds and outputs via the press of a button.
All these things are covered on Talking Electronics website and you don't have to buy any books or publications. Everything is available on the web and it is instantly accessible. That's the beauty of the web.
Don't think things are greener on the other side of the fence, by buying a text book. They aren't. Everything you need is on the web AT NO COST.
The only thing you have to do is build things. If you have any technical problem at all, simply email Colin Mitchell and any question will be answered. Nothing could be simpler and this way we guarantee you SUCCESS. Hundreds of readers have already emailed and after 5 or more emails, their circuit works. That's the way we work. One thing at a time and eventually the fault is found.
If you think a circuit will work the first time it is turned on, you are fooling yourself.
All circuits need corrections and improvements and that's what makes a good electronics person. Don't give up. How do you think all the circuits in these eBooks were designed? Some were copied and some were designed from scratch but all had to be built and adjusted slightly to make sure they  worked perfectly.
I don't care if you use bread-board, copper strips, matrix board or solder the components in the air as a "bird's nest."  You only learn when the circuit gets turned on and WORKS!
In fact the rougher you build something, the more you will guarantee it will work when built on a printed circuit board.
A circuit board tightens up the circuit and makes it perform better. Take the LED driver circuit below. Without the 100u, the LEDs were fairly bright on a set of AA cells.  When the 100u was added, the current increased and the brightness improved enormously. The 100u has the effect of reducing the impedance of the power supply and allows a higher instantaneous current to be drawn.

 

 

 

 

CONTENTS


Book Light
Camera Activator
Circuit Symbols Complete list of Symbols
Colour Code for Resistors - all resistors
Constant Current
Dark Detector with beep Alarm
Decaying Flasher
Increasing the output current
Latching Relay
LED Detects light


Power Supplies - Fixed
Power Supplies - Adjustable LMxx series
 Power Supplies - Adjustable 78xx series
Power Supplies - Adjustable from 0v
Resistor Colour Code
Resistor Colour Code - 4, 5 and 6 Bands
Soft Start power supply
Train Detectors
Transformerless Power Supply
1-watt LED
1.5 watt LED
3-Phase Generator
5v from old cells
20 LEDs on 12v supply

 
RESISTOR COLOUR CODE
See resistors from 0.22ohm to 22M in full colour at end of book and another resistor table  


DARK DETECTOR with beep-beep-beep Alarm
 This circuit detects darkness and produces a beep-beep-beep alarm. The first two transistors form a high-gain amplifier with feedback via the 4u7 to produce a low-frequency oscillator. This provides voltage for the second oscillator (across the 1k resistor) to drive a speaker.
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3-PHASE SINEWAVE GENERATOR
This circuit produces a sinewave and each phase can be tapped at the point shown.
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 TRANSFORMERLESS POWER SUPPLY
This clever design uses 4 diodes in a bridge to produce a fixed voltage power supply capable of supplying 35mA.
All diodes (every type of diode) are zener diodes. They all break down at a particular voltage. The fact is, a power diode breaks down at 100v or 400v and its zener characteristic is not useful.
But if we put 2 zener diodes in a bridge with two ordinary power diodes, the bridge will break-down at the voltage of the zener. This is what we have done. If we use 18v zeners, the output will be 18v + 0.6v. The current is limited by the value of the X2 capacitor and this is 7mA for each 100n when in full-wave (as per this circuit). We have 10 x 100n = 1u capacitance. Theoretically the circuit will supply 70mA but we found it will only deliver 35mA before the output drops. The capacitor should comply with X1 or X2 class. The 10R is a safety-fuse resistor.
The problem with this power supply is the "live" nature of the negative rail. When the power supply is connected as shown, the negative rail is 0.7v above neutral. If the mains is reversed, the negative rail is 340v (peak) above neutral and this will kill you as the current will flow through the diode and be lethal. You need to touch the negative rail (or the positive rail) and any earthed device such as a toaster to get killed. The only solution is the project being powered must be totally enclosed in a box with no outputs.
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BOOK LIGHT
This circuit keeps the globe illuminated for a few seconds after the switch is pressed.
There is one minor fault in the circuit. The 10k should be increased to 100k to increase the "ON" time.
The photo shows the circuit built with surface-mount components:
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CAMERA ACTIVATOR
This circuit was designed for a customer who wanted to trigger a camera after a short delay.
The output goes HIGH about 2 seconds after the switch is pressed. The LED turns on for about 0.25 seconds.
The circuit will accept either active HIGH or LOW input and the switch can remain pressed and it will not upset the operation of the circuit. The timing can be changed by adjusting the 1M trim pot and/or altering the value of the 470k.
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MAKE YOUR OWN:


15 LEDs on Matrix board
The transformer consists of 50 turns 0.25mm wire connected to the pins.
The feedback winding is 20 turns 0.095mm wire with "fly-leads."
1-WATT LED
This circuit drives 15 LEDs to produce the same brightness as a 1-watt LED. The circuit consumes 750mW but the LEDs are driven with high-frequency, high-voltage spikes, and become more-efficient and produce a brighter output that if driven by pure-DC.
The LEDs are connected in 3 strings of 5 LEDs. Each LED has a characteristic voltage of 3.2v to 3.6v making each chain between 16v and 18v. By selecting the LEDs we have produced 3 chains of 17.5v  Five LEDs (in a string) has been done to allow the circuit to be powered by a 12v battery and allow the battery to be charged while the LEDs are illuminating. If only 4 LEDs are in series, the characteristic voltage may be as low as 12.8v and they may be over-driven when the battery is charging. (Even-up the characteristic voltage across each chain by checking the total voltage across them with an 19v supply and 470R dropper resistor.) The transformer is shown above. It is wound on a 10mH choke with the original winding removed. This circuit is called a "boost circuit." It is not designed to drive a single 1-watt LED (a buck circuit is needed).
The LEDs in the circuit are 20,000mcd with a viewing angle of 30 degrees (many of the LED specifications use "half angle." You have to test a LED to make sure of the angle).  This equates to approximately 4 lumens per LED. The 4-watt CREE LED claims 160 lumens (or 40 lumens per watt). Our design is between 50 - 60 lumens per watt and it is a much-cheaper design.

 
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30 LEDs on Matrix board

 1.5 WATT LED
The circuit below can be modified to drive up to 30 white LEDs.
The effectiveness of a LED array increases when they are spread out slightly and this makes them more efficient than a single 1 watt or 2 watt LED.
The two modifications to the circuit make the BC337 work harder and this is the limit of the inductor.  The current consumption is about 95mA.
The winding details for the transformer are shown above.

 
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DRIVE 20 LEDs FROM 12v - approx 1watt circuit
This is another circuit that drives a number of LEDs or a single 1 watt LED. It is a "Buck Circuit" and drives the LEDs in parallel. They should be graded so that the characteristic voltage-drop across each of them is within 0.2v of all the other LEDs. The circuit will drive any number from 1 to 20 by changing the "sensor" resistor as shown on the circuit. The current consumption is about 95mA @ 12v and lower at 18v. The circuit can be put into dim mode by increasing the drive resistor to 2k2.  The UF4004 is an ultra fast 1N4004 - similar to a high-speed diode.  You can use 2 x 1N4148 signal diodes.
The circuit will not drive two LEDs in series - it runs out of voltage (and current) when the voltage across the load is 7v. It oscillates at approx 200kHz. Build both the 20 LED and 1 watt LED version and compare the brightness and effectiveness.
The photo of the 1 watt LED on the left must be heatsinked to prevent the LED overheating. The photo on the circuit diagram shows the LED mounted on a heatsink and the connecting wires.


             A 1-watt demo board showing the complex step-up circuitry.
This is a Boost circuit to illuminate the LED and is completely different to our design.  It has been included to show the size of a 1 watt LED.
The reason for a Boost or Buck circuit to drive one or more LEDs is simple. The voltage across a LED is called a "characteristic voltage" and comes as a natural feature of the LED. We cannot alter it. To power the LED with exactly the correct amount of voltage (and current) you need a supply that is EXACTLY the same as the characteristic voltage. This is very difficult to do and so a resistor is normally added in series. But this resistor wastes a lot of energy. So, to keep the loses to a minimum, we pulse the LED with bursts of energy at a higher voltage and the LED absorbs them and produces light. With a Buck circuit, the transistor is turned on for a short period of time and illuminated the LEDs. At the same time, some of the energy is passed to the inductor so that the LEDs are not damaged. When the transistor is turned off, the energy from the inductor also gives a pulse of energy to the LEDs. When this has been delivered, the cycle starts again.    

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POWER SUPPLIES - FIXED:


A simple power supply can be made with a component called a "3-pin regulator or 3-terminal regulator"  It will provide a very low ripple output (about 4mV to 10mV provided electrolytics are on the input and output.
The diagram above shows how to connect a regulator to create a power supply. The 7805 regulators can handle 100mA, 500mA and 1 amp, and produce an output of 5v, as shown.
These regulators are called linear regulators and drop about 4v across them - minimum. If the current flow is 1 amp, 4watts of heat must be dissipated via a large heatsink. If the output is 5v and input 12v,  7volts will be dropped across the regulator and 7watts must be dissipated.
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POWER SUPPLIES - ADJUSTABLE:

The LM317 regulators are adjustable and produce an output from 1.25 to about 35v. The LM317T regulator will deliver up to 1.5amp.
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POWER SUPPLIES - ADJUSTABLE using 7805:

The 7805 range of regulators are called "fixed regulators" but they can be turned into adjustable regulators by "jacking-up" their output voltage. For a 5v regulator, the output can be 5v to 30v.
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POWER SUPPLIES - ADJUSTABLE from 0v:

The LM317 regulator is adjustable from 1.25 to about 35v. To make the output 0v to 35v, two power diodes are placed as shown in the circuit. Approx 0.6v is dropped across each diode and this is where the 1.25v is "lost."
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CONSTANT CURRENT
This constant current circuit can be adjusted to any value from a few milliamp to about 500mA - this is the limit of the BC337 transistor.
The circuit can also be called a current-limiting circuit and is ideal in a bench power supply to prevent the circuit you are testing from being damaged.
Approximately 4v is dropped across the regulator and 1.25v across the current-limiting section, so the input voltage (supply) has to be 5.25v above the required output voltage.  Suppose you want to charge 4 Ni-Cad cells. Connect them to the output and adjust the 500R pot until the required charge-current is obtained.
The charger will now charge 1, 2, 3 or 4 cells at the same current. But you must remember to turn off the charger before the cells are fully charged as the circuit will not detect this and over-charge the cells.
The LM 317 3-terminal regulator will need to be heatsinked.
This circuit is designed for the LM series of regulator as they have a voltage differential of 1.25v between "adj" and "out" terminals.
7805 regulators can be used but the losses in the BC337 will be 4 times greater as the voltage across it will be 5v.
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The regulator connected to a 12v battery pack


The regulator connected to a 9v battery

  


The battery snap plugs into the pins on the 5v regulator board with the red lead going to the negative output of the board as the battery snap is now DELIVERING voltage to the circuit you are powering.



 

A close-up of the regulator module

  
 
5v FROM OLD CELLS
This circuit takes the place of a 78L05 3-terminal regulator. It produces a constant 5v  @ 100mA. You can use any old cells and get the last of their energy. Use an 8-cell holder. The voltage from 8 old cells will be about 10v and the circuit will operate down to about 7.5v. The regulation is very good at 10v, only dropping about 10mV for 100mA current flow (the 78L05 has 1mV drop).  As the voltage drops, the output drops from 5v on no-load to 4.8v and 4.6v on 100mA current-flow. The pot can be adjusted to compensate for the voltage-drop.
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INCREASING THE OUTPUT CURRENT
The output current of all 3-terminal regulators can be increased by including a pass transistor. This transistor simply allows the current to flow through the collector-emitter leads.
The output voltage is maintained by the 3-terminal regulator but the current flows through the "pass transistor." This transistor is a power transistor and must be adequately heatsinked.
Normally a 2N3055 or TIP3055 is used for this application as it will handle up to 10 amps and creates a 10 amp power supply.  The regulator can be 78L05 as all the current is delivered by the pass transistor.
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SOFT START
The output voltage of a 3-terminal regulator can be designed to rise slowly. This has very limited application as many circuits do not like this.
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LED DETECTS LIGHT
The LED in this circuit will detect light to turn on the oscillator. Ordinary red LEDs do not work. But green LEDs, yellow LEDs and high-bright white LEDs and red LEDs work very well.
The output voltage of the LED is up to 600mV when detecting  very bright illumination.
When light is detected by the LED, its resistance decreases and a very small current flows into the base of the first transistor. The transistor amplifies this current about 200 times  and the resistance between collector and emitter decreases. The 330k resistor on the collector is a current limiting resistor as the middle transistor only needs a very small current for the circuit to oscillate. If the current is too high, the circuit will "freeze."
The piezo diaphragm does not contain any active components and relies on the circuit to drive it to produce the tone.
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TRAIN DETECTORS
In response to a reader who wanted to parallel TRAIN DETECTORS, here is a diode OR-circuit. The resistor values on each detector will need to be adjusted (changed) according to the voltage of the supply and the types of detector being used. Any number of detectors can be added. See Talking Electronics website for train circuits and kits including Air Horn, Capacitor Discharge Unit for operating point motors without overheating the windings, Signals, Pedestrian Crossing Lights and many more. 
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DECAYING FLASHER
In response to a reader who wanted a flashing LED circuit that slowed down when a button was released, the above circuit increases the flash rate to a maximum and when the button is released, the flash rate decreases to a minimum and halts.
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LATCHING RELAY
 To reduce the current in battery operated equipment a relay called  LATCHING RELAY can be used. This is a relay that latches itself ON when it receives a pulse in one direction and unlatches itself when it receives a pulse in the other direction.
The following diagram show how the coil makes the magnet click in the two directions.

  
To operate this type of relay, the voltage must be reversed to unlatch it. The circuit above produces a strong pulse to latch the relay ON and the input voltage must remain HIGH. The 220u gradually charges and the current falls to a very low level. When the input voltage is removed, the circuit produces a pulse in the opposite direction to unlatch the relay.


 

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Circuit Symbols
 The list below covers almost every symbol you will find on an electronic circuit diagram. It allows you to identify a symbol and also draw circuits. It is a handy reference and has some symbols that have never had a symbol before, such as a Flashing LED and electroluminescence panel.
Once you have identified a symbol on a diagram you will need to refer to specification sheets to identify each lead on the actual component.
The symbol does not identify the actual pins on the device. It only shows the component in the circuit and how it is wired to the other components, such as input line, output, drive lines etc. You cannot relate the shape or size of the symbol with the component you have in your hand or on the circuit-board.  
Sometimes a component is drawn with each pin in the same place as on the chip etc. But this is rarely the case.
Most often there is no relationship between the position of the lines on the circuit and the pins on the component.

That’s what makes reading a circuit so complex.

This is very important to remember with transistors, voltage regulators, chips and so many other components as the position of the pins on the symbol are not in the same places as the pins or leads on the component and sometimes the pins have different functions according to the manufacturer.  Sometimes the pin numbering is different according to the component, such as positive and negative regulators.

You must to refer to the manufacturer’s specification sheet to identify each pin, to be sure you have identified them correctly.


Colin Mitchell


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IC PINOUTS
 The following list covers just a few of the IC's on the market and these are the "simple" or "basic" or "digital" or "op-amp" IC's suitable for experimenting.
When designing a circuit around an IC, you have to remember two things:
1. Is the IC still available? and
2. Can the circuit be designed around a microcontroller?
Sometimes a circuit using say 3 or 4 IC's can be re-designed around an 8-pin or 16-pin microcontroller and the program can be be kept from prying eyes due to a feature called "code protection." A microcontroller project is more up-to-date, can be cheaper and can be re-programmed to alter the features.
This will be covered in the next eBook. It is worth remembering - as it is the way of the future.


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All the resistor colours: