800m FM Transmitter 9v battery

This is one of the smallest and neatest FM transmitters to be presented as a construction project and it has the advantage of being available as a complete kit of parts. This will save going to a number of suppliers as no single supplier has all the necessary components.
The circuit has been specially designed to demonstrate the techniques of FM transmission and to start you in the world of surface-mount assembly.
FM transmission is the best mode for transmitting a signal as it does not suffer from interference such as electrical noise from car engines or electrical appliances etc. It also achieves the greatest range with the least power.
With just a handful of components and a few milliwatts of output power you can produce an FM transmitter with a very impressive range and perfect clarity.

SUMMARY OF SPECIFICATIONS

Supply: 9 volts
Current consumption: 7mA
Battery life: 50 hours ZnC    100 hours alkaline
Tuning range: 80 - 110MHz (by stretching or compression the oscillator coil)
Fine tune by adjusting the air trimmer (2MHz adjustment)
Stability - Low. Bug to be left in-place and not to be moved or handled.
Antenna length - 175cm (5ft 9in)

 With a 175cm (5ft 9in) (half-wave antenna) supplied in the kit, the range has been conservatively rated as 800 metres (2400ft) under normal working conditions. In many countries you must reduce the maximum range to 30ft (10metres) by cutting the antenna to 10 inches. If this is the case, you must abide by it. Some countries totally ban these brilliant devices. You need to find out the situation in your own locality.
To introduce surface-mount technology to our range of projects, we have started with resistors. These are the easiest of the surface-mount components to identify and fit.
Some of the other components such as capacitors and transistors are so small they are almost impossible to solder by hand and surface-mount capacitors are not marked in any way so they become easily mixed up if you are not very careful.
Surface-mount technology is entirely different to normal through-hole placement and some of the differences are explained in this article.
The major difference is size and if you are having trouble soldering 1/4 watt resistors, you will have ten times more difficulty with surface mount. SM items are so small it takes the keenest eyesight to read the figures on the component and the nimblest of fingers to pick them up and place them.
But until you buy a kit and see what the parts look like, you will have no idea if you will be able to cope.
Nevertheless surface mount has arrived and is here to stay. Most modern designs already include surface mount components and many are already entirely surface mount. Take pocket cameras, watches, pendant transmitters, toys, video recorders, video cameras and computers for example. Their miniaturisation has been almost entirely due to using smaller componentry.
Surface mount is very easy to implement on a large scale as the components are available in large quantities on reels or in tubes but when it comes to a one-off project, things are different. Few suppliers sell individual surface-mount components and some sell them in lots of 10 or 100. The normal purchase for surface-mount is on a reel of 1,000 to 5,000 pieces.
The only solution is to provide a kit and to make it easy for everyone to put together, we have just converted the resistors to surface-mount.
Some of the other components are not available in surface-mount (such as the coil) and there is no real advantage in converting everything to surface mount as the battery cannot be reduced in size without reducing the number of hours of operation.
The main difficulty with surface mount is placing them on the printed circuit board and holding them in place while soldering. There are a number of aids to help you do this, such as solder pastes and solder creams, silicon and infra-red setting glues but most of these come in syringes and cost as much as $20 for a 1oz (30gm) tube. For a simple project, this additional cost is out of the question.
To keep costs down we are going to hand solder each resistor without the aid of glue and the technique we use is called RE-FLOW SOLDERING.
Re-flow soldering only requires two hands. Normal soldering requires three hands - one to hold the component in place, one to hold the soldering iron and one to hold the solder. If you have three hands available, (such as the help of an assistant), you can use the normal soldering method.
Basically re-flow soldering consists of heating up the solder on the board AND THE END OF THE RESISTOR AT THE SAME TIME so that the resistor makes a perfect connection to the board. This is discussed fully in the soldering section.

HOW THE CIRCUIT WORKS
The circuit consists of two stages - an audio amplifier and an RF oscillator.
The electret microphone contains a FET transistor and can be counted as a stage, if you wish. The microphone detects audio in the form of air vibrations that enter the hole (at the end of the mic) and move the diaphragm. This diaphragm is a thin piece of metallised plastic such as mylar and is charged with electrical charges during manufacture.
Next to this is a metal plate containing a number of holes so that the air readily passes through. The relative distance of the mylar diaphragm to the metal plate makes the charges move on the diaphragm (remember static electricity theory: like-charges repel and unlike-charges attract). Some of the charges pass down a lead that touches the metal plate and into a FET amplifier - it looks like a three legged transistor. The FET amplifies the charges and gives a reading on the output lead.
The output must be connected to a supply via a resistor called the load resistor. The FET draws a varying current during its operation and this creates a varying voltage on the output (across the load resistor).
The reason why a FET has been used is due to it having a very high input impedance and does not have any loading effect on the charges.
The output waveform from the microphone will be typically 3 - 30mV in our case, depending on how close it is to the source of the sound. The circuit is capable of detecting a whisper at 10ft (3M) and only very sensitive microphones have been included in the kits.
You can also get medium and low sensitivity devices from suppliers so you have to be careful as they are not labelled.
A 22n capacitor on the output of the microphone couples the signal to the input of the first audio amplifier stage. This capacitor is designed to separate the DC voltage on the microphone from the base voltage on the transistor.
The first transistor stage consists of transistor and two biasing resistors.
The stage is said to be "AC coupled" as it has a capacitor on both the input and output so the DC voltages of the other stages do not influence the voltage on the stage.
The stage is also said to be "self-biased" with the 1M base resistor turning the transistor on until the collector voltage drops to about half rail voltage. The value of the base resistor is chosen so that this occurs.
The value can be chosen by experimentation. If the value is too low, the voltage on the collector will be below half rail. If it is too high, the collector voltage will be too high. The AC gain of the stage is about 70 and the signal is amplified and passed to the oscillator stage via a 100n capacitor.
The signal is now typically 200mV to 2,000mV in amplitude and this is adequate for injection into the oscillator stage.
The oscillator stage is designed to operate at about 100MHz and this frequency is set by the value of inductance of the 5 turn coil and the capacitor(s) across it. The 39p and air trimmer can be considered as a single capacitor. The frequency is also determined to a lesser extent by the transistor, the 10p feedback capacitor and also the 470R emitter biasing resistor and the 47k base bias resistor. The supply voltage also has an effect as the oscillator can be classified as voltage controlled.
There are a lot of things that set the frequency and even though the parts have a 5%, 10% or even 20% tolerance, they are STABLE at their present value. The 10p and 39p are NPO types and this means they are stable even when the temperature changes a small amount. The frequency is firstly set by pushing the turns of the coil closer together to lower the frequency or pulling them apart to raise the frequency and then the air trimmer is adjusted to obtain the precise frequency required. The air trimmer has a range of about 2MHz.
The circuit will stay at the desired frequency providing the supply voltage remains constant and the temperature of the parts do not rise appreciably (such as when the project is left in the sun etc).
Voyager MkII is not designed to be handled and is not suitable to be worn on the body. It is designed to be placed on a shelf and left in position.
The most important components in the oscillator stage are the coil and capacitor(s), making up the parallel tuned circuit. 
They do almost all the work in setting the frequency and generating the waveform. The transistor merely turns on at the correct instant in each cycle to deliver a small amount of energy to the tuned circuit. 
How this is done: The transistor is firstly turned on via base-bias resistor and it injects a small amount of energy into the parallel tuned circuit.  A few low-amplitude cycles now take place and we pick up the operation when the tuned circuit is operating at full amplitude and producing a sinewave at about 100MHz. This frequency is called the CARRIER.
The parallel tuned circuit is also called a TANK CIRCUIT and the name was coined during the development of the earliest transmitters where it was found a coil and capacitor in parallel would smooth out electrical pulses like filling a water tank in bursts so that it delivers an even flow of water.
This name has stayed with us and is an ideal way of describing a coil/capacitor combination.
The waveform from the tank circuit is passed to the 10p and this modifies the voltage on the emitter of the transistor.
There are two ways of turning on a transistor. One is to raise the voltage on the base while holding the emitter fixed and the other is to hold the base rigid while lowering the voltage on the emitter.
The second method is used in this circuit and the 10p moves the emitter up a very small amount at the rate of 100 million times per second to turn the transistor off.
The base is held rigid via a 1n capacitor and this value is sufficient to hold the base rigid at 100MHz but allows it to move up and down at audio frequencies so that audio being processed by the first transistor can be passed to the oscillator.
The oscillator transistor does not determine the waveshape of the signal, it mainly delivers a pulse of energy to the tank circuit at the correct instant where the coil and capacitor do all the work in creating the carrier signal. There is one more feature of the tank circuit. Even though it is injected with a pulse of energy of only a few millivolts, it is capable of producing a higher amplitude waveform on its output. In other words the tank circuit is capable of amplifying the voltage supplied to it. This is called its Q-factor.
The other two components in the stage are the 47k base-bias resistor and 470R emitter resistor. The 47k turns the transistor on when the power is first applied and sets the operating point for the stage. The 470R emitter resistor acts as a current limiting resistor and allows the transistor to be injected via the emitter.
The voltage produced by the tank circuit is monitored by the 10p and passed to the emitter of the transistor. During a portion of the cycle, the voltage it delivers, turns the transistor off. This effectively removes the transistor from the circuit and allows the waveform from the tank circuit to be passed to the antenna.
When a waveform at 100MHz is passed into a wire (such as an antenna) the signal is very easily radiated as electromagnetic energy. This is how the signal is radiated to the surroundings.
The 22n supply capacitor across the battery is designed to tighten up the power rails. The power rails have also been kept tight by connecting the battery directly to the printed circuit board.
Note: The circuit will not operate from a power supply without generating a lot of "mains hum" - the annoying 100 or 120 cycle hum from the mains - you must use a battery to get a crystal clear, hum-free, output.
Test voltages have been provided on the circuit diagram to help with servicing. They are only approximate and apply to our prototype. They show how each transistor has a voltage on the base of about 0.6v, with respect to the emitter, to turn it on.
The voltages around the oscillator stage cannot be measured with an ordinary multimeter when the circuit is operating as the leads of the multimeter will act as an antenna and kill the operation of the circuit. This is certainly the case on the emitter of the second transistor, where the leads of a multimeter will draw off so much energy that the stage will stop working.
Because you cannot detect the operation with a multimeter, we have developed a piece of test equipment called a LED POWER METER. This is covered below and shows how the output of the high frequency RF oscillator stage can be measured without loading it too much.
 

FM Transmitter with double transistor

The next progressive step is to add a transistor to give the electret microphone more sensitivity. The electret microphone contains a Field Effect Transistor and you can consider it to be a stage of amplification. That's why the electret microphone has a very good output.
A further stage of amplification will give the bug extremely good sensitivity and you will be able to pick up the sound of a pin dropping on a wooden floor.
Many of the 1 transistor circuits over-drive the microphone and this will create a noise like bacon-and-eggs frying. The microphone's used by Talking Electronics require a load resistor of 47k for a 6v supply and 22k for a 3v supply. The voltage across the microphone is about 300mV to 600mV. It will produce an audio waveform of about 2-20mV.
Only a very simple self-biasing common-emitter stage is needed for the audio amplifier. This will give a gain of approx 70 for a 3v supply. The next circuit shows this audio amplifier, added to the previous transmitter circuit. This circuit is the best design using 2 transistors on a 3v supply. The circuit takes about 7mA and produces a range of about 200 - 400metres.

2 Transistor FM Transmitter

Five points to note in the circuit above:
1. The tank circuit has a fixed 39p and is adjusted by a 2-10p trimmer. The coil is stretched to get the desired position on the band and the trimmer fine tunes the location.
2. The microphone coupling is a 22n ceramic. This value is sufficient as its capacitive reactance at 3-4kHz is about 4k and the input to the audio stage is fairly high, as noted by the 1M on the base.
3. The 1u between the audio stage and oscillator is needed as the base has a lower impedance as noted by the 47k base-bias resistor.
4. The 22n across the power rails is needed to keep the rails "tight." Its impedance at 100MHz is much less than one ohm and it improves the performance of the oscillator enormously. 
5. The coil in the tank circuit is 5 turns of enameled wire with air core. This is much better than a coil made on a PC board and is cheaper than a bought inductor. The secret to long range is high activity in the oscillator stage. The tank circuit (made up of the coil and capacitors across it) will produce a voltage higher than the supply voltage due to the effect known as "collapsing magnetic field"  and this occurs when the coil collapses and passes its reverse voltage to the capacitor. The antenna is also connected to this point and it receives this high waveform and passes the energy to the atmosphere as electromagnetic radiation.
When the circuit is tightly constructed on a PC board, the frequency will not drift very much if the antenna is touched. This is due to the circuit design and layout as well as the use of large-value capacitors in the oscillator. If low value capacitors are used, the effect of your body has a greater effect on changing the frequency. 

Fm Transmitter PNP Design

Before we go to an improved design, here is an unusual circuit using a PNP (BC 557) transistor. Firstly, PNP transistors do not work as well as NPN transistors. I would reverse the 4k7 and electret mic as the voltage between base and 0v rail is very small and the 4k7 is not biasing the transistor - it is not needed! The range will be 50 to 100 metres and the current is about 3mA.
Note: A reader built this circuit. It did not work!!
Try putting the 47p across the coil. The 33p may need to be reduced to 10p.
It is just a BAD design, but a good challenge to see if you can get this type of design to work.
 

Simple 1 transistor FM Transmitter

The 22n is not shown. This is a later addition.

FM Transmitter Bad Layout

Here is a circuit with a very bad layout. The circuit may work but it relies on a "Q-factor" from the coil and capacitor in the tank circuit to produce a high voltage. This high voltage gives the circuit a good range.
Firstly the coil and capacitor should be near each other. The coil should not have long leads. and a 22n capacitor should be across the supply to give the circuit better performance. The value of C2 is too high. It should be 10p. The coil should be 5 turns. The electret mic should not be connected directly to the base of the transistor. As you can see, the circuit is full of faults.
You can learn a lot from other people's mistakes.   

Simplest FM Transmitter

The following circuit is the simplest FM circuit you can get. It has no microphone but the coil is so MICROPHONIC that it will pick up noises in the room via vibrations on a table.
The circuit does not have any section that determines the frequency. In the next circuit and all those that follow, the section that determines the frequency of operation is called the TUNED CIRCUIT or TANK CIRCUIT and consists of a coil and capacitor. The transistor and components surrounding the tuned circuit simply keep the tuned circuit operating at its RESONANT FREQUENCY. This circuit does not have this feature. The transistor turns on via the 47k and this puts a pulse through the 15 turn winding. The magnetic flux from this winding passes through the 6 turn winding and into the base of the transistor via the 22n capacitor. This pulse is amplified by the transistor and the circuit is kept active.
The frequency is determined by the 6 turn coil. By moving the turns together, the frequency will decrease.  The circuit transmits at 90MHz. It has a very poor range and consumes 16mA.

 THE SIMPLEST BUG

  The components soldered to the 2 cells

Rear view of the simplest bug

FM Transmitter with one transistor

This is clearly shown in the diagram. For best performance the circuit should be built on a PC board with all components fitted close to each other. The photo below shows the circuit using a coil etched on the board. This type of coil is totally unsuitable. It does not have a high "Q" and the range is very poor. The board cannot be touched as the capacitance of your body causes the circuit to drift. A wound coil will improve the stability considerably. See photos below for the details of a wound coil.

A one transistor circuit

Do not use an etched coil

Here is the 1-transistor circuit produced by GuEsTyE.net on a home-made PC board and heat-shrunk so the air-trimmer is adjustable via a small hole.

The PC board drilled ready for fitting the components

The 10 components (plus heatshrink, battery and wire)

The components mounted on the board

The board ready for fitting into heatshrink

The finished bug with "studs" for the battery
and a cut-out for the air trimmer

At On Air

Simple FM transmitter with a single transistor

  Mini FM transmitters take place as one of the standard circuit types in an amateur electronics fan's beginning steps. When done right, they provide very clear wireless sound transmission through an ordinary FM radio over a remarkable distance. I've seen lots of designs through the years, some of them were so simple, some of them were powerful, some of them were hard to build etc.

  Here is the last step of this evolution, the most stable, smallest, problemless, and energy saving champion of this race. Circuit given below will serve as a durable and versatile FM transmitter till you break or crush it's PCB. Frequency is determined by a parallel L-C resonance circuit and shifts very slow as battery drains out.

 Technical datas:

 Supply voltage    :    1.1 - 3 Volts

 Power consumption :    1.8 mA at 1.5 Volts

 Range             :    30 meters max. at 1.5 Volts

  Main advantage of this circuit is that power supply is a 1.5Volts cell (any size) which makes it possible to fix PCB and the battery into very tight places. Transmitter even runs with standard NiCd rechargeable cells, for example a 750mAh AA size battery runs it about 500 hours (while it drags 1.4mA at 1.24V) which equals to 20 days. This way circuit especially valuable in amateur spy operations :)

  Transistor is not a critical part of the circuit, but selecting a high frequency / low noise one contributes the sound quality and range of the transmitter. PN2222A, 2N2222A, BFxxx series, BC109B, C, and even well known BC238 runs perfect. Key to a well functioning, low consumption circuit is to use a high hFE / low Ceb (internal junction capacity) transistor.

  Not all of the condenser microphones are the same in electrical characteristics, so after operating the circuit, use a 10K variable resistance instead of the 5.6K, which supplies current to the internal amplifier of microphone, and adjust it to an optimum point where sound is best in amplitude and quality. Then note the value of the variable resistor and replace it with a fixed one.

  The critical part is the inductance L which should be handmade. Get an enameled copper wire of 0.5mm (AWG24) and round two loose loops having a diameter of 4-5mm. Wire size may vary as well. Rest of the work is much dependent on your level of knowledge and experience on inductances:  Have an FM radio near the circuit and set frequency where is no reception. Apply power to the circuit and put a iron rod into the inductance loops to chance it's value. When you find the right point, adjust inductance's looseness and, if required, number of turns. Once it's OK, you may use trimmer capacitor to make further frequency adjustments. You may get help of a experienced person on this point. Do not forget to fix inductance by pouring some glue onto it against external forces. If the reception on the radio lost in a few meters range, than it's probably caused by a wrong coil adjustment and you are in fact listening to a harmonic of the transmitter instead of the center frequency. Place radio far away from the circuit and re-adjust. An oscilloscope would make it easier, if you know how to use it in this case. Unfortunately I don't have any :(

  Every part should fit on the following PCB easily. Pay attention to the transistor's leads which should be connected right. Also try to connect trimmer capacitor's moving part to the + side, which may help unwanted frequency shift while adjusting. PCB drawing should be printed at 300DPI.

   The one below is a past PCB work of mine, which was prepared to fit into a pocket flashlight. Since it was so crowded, use the new computerized PCB artwork instead, yet very small.

   Here is a completed and perfectly running circuit, mounted in a pocket light, taking the advantage of the 1.5V AA cell slot near it. Microphone is fixed into the bulb's place and antenna is made out of a 30cm soft cable. When cover is placed, it becomes very handy!

   Do not forget, restrictions on radio frequency transmitting devices may differ in your local area. This circuit has a power output that should be less than 1mW so have to be safe under many kinds of legal conditions but particular attempts such as listening to other people's private life will always be disapproved everywhere.

Fading Red Eyes

This circuit is used to slowly illuminate and fade a pair of red LEDs (light emitting diodes). The fading LEDs could be installed as 'eyes' in a small pumpkin or skull as a Halloween attraction, or mounted in a Christmas tree ornament. Or, they might be used as a fancy power indicator for your computer, microwave oven, stereo system, TV, or other appliance.
In operation, a linear 3 volt (peak to peak) ramping waveform is generated at pin 1 of the LM1458 IC and buffered with an emitter follower transistor stage. The 22uF capacitor and 47K resistor connected to pin 2 establish the frequency which is about 0.5 Hz. You can make the rate adjustable by using a 100K potentiometer in place of the 47K resistor at pin 2.
The circuit consists of two operational amplifiers (opamps), one producing a slow rising and falling voltage from about 3 volts to 6 volts, and the other (on the right) is used as a voltage comparator, the output of which supplies a alternating voltage switching between 2 and 7 volts to charge and discharge the capacitor with a constant current.
Each of the op-amps has one of the inputs (pins 3 and 6) tied to a fixed voltage established by two 47K resistors so that the reference is half the supply voltage or 4.5 volts. The left opamp is connected as an inverting amplifier with a capacitor placed between the output (pin 1) and the inverting input (pin 2). The right opamp is connected as a voltage comparator so that the output on pin 7 will be low when the input is below the reference and high when the input is higher than the reference. A 100K resistor is connected between the comparator output and input to provide positive feedback and pulls the input above or below the switching point when the threshold is reached. When the comparator output changes at pin 7, the direction of the current changes through the capacitor which in turn causes the inverting opamp to move in the opposite direction. This yields a linear ramping waveform or triangle waveform at pin 1 of the inverting opamp. It is always moving slowly up or down, so that the voltage on the non-inverting input stays constant at 4.5 volts.
Adjustments to the point where the LEDs extinguish can be made by altering the resistor value at pin 3 and 6 to ground. I found a 56K in place of the 47k shown worked a little better with the particular LEDs used. You can experiment with this value to get the desired effect.

How to build Fading Red Eyes

Circuit description:
This circuit is used to slowly illuminate and fade a pair of red LEDs (light emitting diodes). The fading LEDs could be installed as 'eyes' in a small pumpkin or skull as a Halloween attraction, or mounted in a Christmas tree ornament. Or, they might be used as a fancy power indicator for your computer, microwave oven, stereo system, TV, or other appliance.
In operation, a linear 3 volt (peak to peak) ramping waveform is generated at pin 1 of the LM1458 IC and buffered with an emitter follower transistor stage. The 22uF capacitor and 47K resistor connected to pin 2 establish the frequency which is about 0.5 Hz. You can make the rate adjustable by using a 100K potentiometer in place of the 47K resistor at pin 2.
The circuit consists of two operational amplifiers (opamps), one producing a slow rising and falling voltage from about 3 volts to 6 volts, and the other (on the right) is used as a voltage comparator, the output of which supplies a alternating voltage switching between 2 and 7 volts to charge and discharge the capacitor with a constant current.
Each of the op-amps has one of the inputs (pins 3 and 6) tied to a fixed voltage established by two 47K resistors so that the reference is half the supply voltage or 4.5 volts. The left opamp is connected as an inverting amplifier with a capacitor placed between the output (pin 1) and the inverting input (pin 2). The right opamp is connected as a voltage comparator so that the output on pin 7 will be low when the input is below the reference and high when the input is higher than the reference. A 100K resistor is connected between the comparator output and input to provide positive feedback and pulls the input above or below the switching point when the threshold is reached. When the comparator output changes at pin 7, the direction of the current changes through the capacitor which in turn causes the inverting opamp to move in the opposite direction. This yields a linear ramping waveform or triangle waveform at pin 1 of the inverting opamp. It is always moving slowly up or down, so that the voltage on the non-inverting input stays constant at 4.5 volts.
Adjustments to the point where the LEDs extinguish can be made by altering the resistor value at pin 3 and 6 to ground. I found a 56K in place of the 47k shown worked a little better with the particular LEDs used. You can experiment with this value to get the desired effect.

Parts List:

• Description - Mfg Part# -Allied Part# - Quantity - Cost
• Operational Amplifier LM1458 - 288-1090 - 1 - .48
• 47K Resistor - 296-2182 - 4 - .42
• 100K Resistor - 296-5610 - 1
• 100 Ohm Resistor - 895-0465 - 1 - .24
• Transistor 2N3904 - 568-8253 - 1 - .1
• 22uF Capacitor - 852-6516 - 1 - .07
• Solderless Breadboard - 237-0015 - 1 - 6.99
• Red Light Emitting Diode (LED) - 670-1224 - 2 - 0.50

Note: The LED listed has a narrow viewing angle of 30 degrees and appears brightest when looking directly at it. It's not a pure red color, and a little on the orange side, but should be brighter compared to other selections. For a wider viewing angle at reduced intensity, try part number 670-1257 which is viewable at 60 degrees and has a red diffused lens.

Construction details:
Layout of the solderless breadboard:
Refer to the drawing below the schematic diagram and note the solderless breadboard is arranged in rows labeled A-J, and columns numbered 1 to 65. Each group of 5 holes in the same column are the same connection, so that holes A1,B1,C1,D1 and E1 are all connected together. Likewise holes F1,G1,H1,I1 and J1 are all the same connection. The outer rows along the length of the board are also connected together and are normally used for power supply connections. However, there is a break in the mid section of the outer rows, so a short jumper wire connecting the mid section of the outer rows should be installed to connect the entire outer row together. If you have a DMM, use the low ohms range and probe the various holes to get familiar with the board layout.
Installing the components:
Orientate the LM1458 so the nook or punch mark on one edge is near column 30 and the opposite edge is near column 33. Install the LM1458 on the breadboard so the pins straddle the center section of the board and pin 1 of the IC is occupying hole E30 and pin 8 is in hole F30. The pins are numbered counter clockwise, so pin 4 will be occupying F33 and pin 5 will be in E33. Possible connections for the LM1458, 9 volt battery, and a couple other parts is illustrated in the lower drawing of the solderless breadboard, but it is not complete with all parts.
Refer to the schematic diagram, and install the various other components so they connect to the appropriate pins of the LM1458. Use whatever connection holes are convenient. For example, the 22uF capacitor connects between pins 1 and 2 of the IC, which occupy holes (F30,F31) so it could be placed in the holes (H30, H31) or (J30,J31) or (I30,I31). But not all parts will conveniently fit, so you may have to use a short jumper wire (#22 preferred) to connect parts from one side of the chip to the other.
The board I assembled was connected this way:

• LM1458 F30 to F33, and E30 to E33
• 22uF capacitor H30 to H31
• 47K resistor I30 to I35
• 47K resistor C27 to C31
• 47K resistor F25 to Positive battery row
• 47K resistor J25 to Negative Battery row
• 100K resistor B31 to B33
• 2N3904 Transistor G36, G37, G38 with emitter at G38
• 100 Ohm resistor D38 to F38
• LED B43 to B44 (Cathode at B44)
• LED I43 to I44 (Cathode at I43)
• Jumper A30 to Positive battery row
• Jumper F36 to Positive battery row
• Jumper J33 to Negative battery row
• Jumper J43 to Negative battery row
• Jumper H25 to J32
• Jumper J30 to J37
• Jumper E27 to G31
• Jumper D32 to G32
• Jumper D33 to H35
• Jumper C38 to C43
• Jumper E44 to F44
• 9 Volt Battery Postive battery row to negative row.

Circuit diagram

 

 The circuit below illustrates two pairs of LEDs that operate out of phase so as one pair slowly illuminate, the other pair will fade. 

 

 

Line Powered White LEDs

The LED circuit below is an example of using 25 white LEDs in series connected to the 120VAC line. It can be modified for more or less LEDs by adjusting the resistor value. The exact resistance will depend on the particular LEDs used. But working out the resistor value is a bit complicated since current will not continously flow through the resistor. In operation, the output of the bridge rectifier will be about 120 DC RMS or 170 volts peak. If we use 25 white LEDs with a forward voltage of 3 volts each, the total LED voltage will be 75 volts. The peak resistor voltage will be 170- 75 or 95 volts but the resistor voltage will not be continous since the input must rise above 75 before any current flows. This (dead time) represents about 26 degrees of the 90 degree half wave rectified cycle, (asin) 75/170 = (asin) .44 = 26 degrees. This means the resistor will conduct during 90-26 = 64 degrees, or about 71 percent of the time.
Next we can work out the peak LED current to determine the resistor value. If the LED current is 20mA RMS, the peak current will be 20*1.414 or 28mA. But since the duty cycle is only 71 percent, we need to adjust this figure up to 28/0.71 = 39mA. So, the resistor value should be 95/.039 = 2436 ohms (2.4K) and the power rating will be .02^2 *2400= .96 watts. A two watt size is recommended.
Now this circuit can also be built using 2 diodes and resistor as shown in the lower drawing. The second diode in parallel with the LEDs is used to avoid a reverse voltage on the LEDs in case the other diode leaks a little bit. It may not be necessary but I thought it was a good idea.
Working out the resistor value is similar to the other example and comes out to about half the value of the full wave version, or about 1.2K at 1 watt in this case. But the peak LED current will be twice as much or about 78mA. This is probably not too much, but you may want to look up the maximum current for short duty cycles for the LEDs used and insure 79mA doesn't exceed the spec.

Black Light

 

This circuit is a simple ultraviolate light that can be powered by a 6 volt battery or power supply that is capable of supplying 1 or more amps.

Parts
C1 0.0047uf Mono Capacitor
C2 0.1uf Disc Capacitor
D1, D2 1N4007 Diode
FTB Filtered Blacklight Tube
IC1 555 Timer IC
P1 10k Trim Pot
Q1 TIP30 PNP Power Transistor
R1 470 Ohm Resistor
R2 270 Ohm Resistor
T1 Medium Yellow Inverter Transformer
MISC IC Socket, Heat Sink For Q1, Screw, Nut, Wire and PC Board
Notes:
1. P1 changes brightness of the black light tube.

AC Line powered LEDs

The circuit below illustrates powering a LED (or two) from the 120 volt AC line using a capacitor to drop the voltage and a small resistor to limit the inrush current. Since the capacitor must pass current in both directions, a small diode is connected in parallel with the LED to provide a path for the negative half cycle and also to limit the reverse voltage across the LED. A second LED with the polarity reversed may be subsituted for the diode, or a tri-color LED could be used which would appear orange with alternating current. The circuit is fairly efficient and draws only about a half watt from the line. The resistor value (1K / half watt) was chosen to limit the worst case inrush current to about 150 mA which will drop to less than 30 mA in a millisecond as the capacitor charges. This appears to be a safe value, I have switched the circuit on and off many times without damage to the LED. The 0.47 uF capacitor has a reactance of 5600 ohms at 60 cycles so the LED current is about 20 mA half wave, or 10 mA average. A larger capacitor will increase the current and a smaller one will reduce it. The capacitor must be a non-polarized type with a voltage rating of 200 volts or more.
The lower circuit is an example of obtaining a low regulated voltage from the AC line. The zener diode serves as a regulator and also provides a path for the negative half cycle current when it conducts in the forward direction. In this example the output voltage is about 5 volts and will provide over 30 milliamps with about 300 millivolts of ripple. Use caution when operating any circuits connected directly to the AC line.

120VAC Lamp Chaser

This circuit is basically the same as the 10 channel LED sequencer with the addition of solid state relays to control the AC lamps. The relay shown in the diagram is a Radio Shack 3 amp unit (part no. 275-310) that requires 1.2 volts DC to activate. No current spec was given but I assume it needs just a few milliamps to light the internal LED. A 360 ohm resistor is shown which would limit the current to 17 mA using a 9 volt supply. I tested the circuit using a solid state relay (of unknown type) which required only 1.5 mA at 3 volts but operates up to 30 volts DC and a much higher current. The chaser circuit can be expanded up to 10 channels with additional relays and driver transistors. The 4017 decade counter reset line (pin 15) is connected to the fifth count (pin 10) so that the lamps sequence from 1 to 4 and then repeat. For additional stages the reset pin would be connected to a higher count.

1.5 Volt LED Flashers

The LED flasher circuits below operate on a single 1.5 volt battery. The circuit on the upper right uses the popular LM3909 LED flasher IC and requires only a timing capacitor and LED.
The top left circuit, designed by Andre De-Guerin illustrates using a 100uF capacitor to double the battery voltage to obtain 3 volts for the LED. Two sections of a 74HC04 hex inverter are used as a squarewave oscillator that establishes the flash rate while a third section is used as a buffer that charges the capacitor in series with a 470 ohm resistor while the buffer output is at +1.5 volts. When the buffer output switches to ground (zero volts) the charged capacitor is placed in series with the LED and the battery which supplies enough voltage to illuminate the LED. The LED current is approximately 3 mA, so a high brightness LED is recommended.
In the other two circuits, the same voltage doubling principle is used with the addition of a transistor to allow the capacitor to discharge faster and supply a greater current (about 40 mA peak). A larger capacitor (1000uF) in series with a 33 ohm resistor would increase the flash duration to about 50mS. The discrete 3 transistor circuit at the lower right would need a resistor (about 5K) in series with the 1uF capacitor to widen the pulse width.

Two Transistor Led Flasher

Infra Red Switch

 This is a single channel (on / off) universal switch that may be used with any Infra Red remote control that uses wavelengths between 850-950nm.

• R1 3k3
• R2 1k
• R3 22k
• R4 220k
• R5 1M
• R6 3k3
• B1 12 V
• D1 1N4148
• D2 1N4003
• Q1 B109
• LED1 CQX35A
• IC1 IR1 available from Harrison Electronics
• IC2 4049
• IC3 CA555
• IC4 SN74HCT74
• IC5 LM7805
• Relay 12 Volt coil with changeover contact
• C1 100u
• C2 22u
• C3 100n
• C4 2u2

Infra-red Level Detector

Useful for liquids level detection and proximity devices
Up to 50 cm. range, optional relay operation

• R1 10K 1/4W Resistor
• R2,R5,R6,R9 1K 1/4W Resistors
• R3 33R 1/4W Resistor
• R4,R8 1M 1/4W Resistors
• R7 10K Trimmer Cermet
• R10 22K 1/4W Resistor
• C1,C4 1µF 63V Electrolytic or Polyester Capacitors
• C2 47pF 63V Ceramic Capacitor
• C3,C5,C6 100µF 25V Electrolytic Capacitors
• D1 Infra-red LED
• D2 Infra-red Photo Diode (see Notes)
• D3,D4 1N4148 75V 150mA Diode
• D5 LED (Any color and size)
• D6,D7 1N4002 100V 1A Diodes
• Q1 BC327 45V 800mA PNP Transistor
• IC1 555 Timer IC
• IC2 LM358 Low Power Dual Op-amp
• IC3 7812 12V 1A Positive voltage regulator IC
• RL1 Relay with SPDT 2A @ 220V switch
• Coil Voltage 12V. Coil resistance 200-300 Ohm
• J1 Two ways output socket

IR Remote Control Tester

As I was developing my IR Extender Circuit, I needed to find a way of measuring the relative intensities of different Infra red light sources. This circuit is the result of my research. I have used a photodiode, SFH2030 as an infra red sensor. A MOSFET opamp, CA3140 is used in the differential mode to amplify the pulses of current from the photodiode. LED1 is an ordinary coloured led which will light when IR radiation is being received. The output of the opamp, pin 6 may be connected to a multimeter set to read DC volts. Infra red remote control strengths can be compared by the meter reading, the higher the reading, the stronger the infra red light. I aimed different remote control at the sensor from about 1 meter away when comparing results. For every microamp of current through the photodiode, about 1 volt is produced at the output. A 741 or LF351 will not work in this circuit. Although I have used a 12 volt power supply, a 9 volt battery will also work here.

IR Remote Control Jammer

Don't like your little brother's TV channel selection? Hate the volume your wife sets the stereo at? Want to just annoy someone? This circuit does all that and more by jamming most IR remote signals. The circuit releases a flood of pulsing IR light that confuses the reciever by corrupting the data stream.

• R1 100K 1/4W Resistor
• R2 150K 1/4W Resistor
• R3 10K 1/4W Resistor
• R4 1K 1/4W Resistor
• R5 See "Notes"
• C1 10nF Ceramic Disc Capacitor
• C2 1uF Electrolytic Capacitor
• D1, D2, D3 High Output IR LED
• Q1 2N4403 PNP Transistor
• Q2 2N4401 NPN Transistor
• S1 Normally Open Momentary Push Botton
• B1 4.5V Battery (Three "AA"'s In Series)
• MISC Wire, Case, Board

IR Receiver Toggle Switch

Light/Dark Detector

This handy little circuit can tell the difference between darkness and light, making it very useful for switching on and off signs, porch lights or other things when it gets dark or light.

• R1 100K Pot
• Q1 2N3904 NPN Transistor or 2N2222
• Q2 NPN Phototransistor
• RELAY 9V Relay
• MISC Board, Wire, 9V Battery Snap (if battery used), Knob For R1

LED Photo Sensor

Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary LED. The LED voltage is buffered by a junction FET transistor and then applied to the inverting input of an op-amp with a gain of about 20. This produces a change of about 5 volts at the output from darkness to bright light. The 100K potentiometer can be set so that the output is around 7 volts in darkness and falls to about 2 volts in bright light.

Photo Electric Street Light

 This is basically a Schmitt Trigger circuit which receives input from a cadmium sulfide photo cell and controls a relay that can be used to switch off and on a street lamp at dawn and dusk. I have built the circuit with a 120 ohm/12 volt relay and monitored performance using a lamp dimmer, but did not connect the relay to an outside light.
The photo cell should be shielded from the lamp to prevent feedback and is usually mounted above the light on top of a reflector and pointed upward at the sky so the lamp light does not strike the photo cell and switch off the lamp.
The photo cell is wired in series with a potentiometer so the voltage at the junction (and base of transistor) can be adjusted to about half the supply, at the desired ambient light level. The two PNP transistors are connected with a common emitter resistor for positive feedback so as one transistor turns on, the other will turn off, and visa versa. Under dark conditions, the photo cell resistance will be higher than the potentiometer producing a voltage at Q1 that is higher than the base voltage at Q2 which causes Q2 to conduct and activate the relay.
The switching points are about 8 volts and 4 volts using the resistor values shown but could be brought closer together by using a lower value for the 7.5K resistor. 3.3K would move the levels to about 3.5 and 5.5 for a range of 2 volts instead of 4 so the relay turns on and off closer to the same ambient light level. The potentiometer would need to be readjusted so that the voltage is around 4.5 at the desired ambient condition.

Dual-rail Variable DC Power Supply

This design was conceived as an add-on for the Variable DC Power Supply, a very successful circuit posted to this website. This simple unit provides a dual-rail variable output ranging from ±2.5V to ±15Vdc with precise tracking of the positive and negative output voltages, still retaining the current limiting and short-proof capabilities of the "master" circuit. As the purpose of such a dual-rail design is to supply experimental or under-repair circuits, the maximum current output delivered was deliberately kept to about 500 - 600mA per rail, thus avoiding the use of expensive power transistors and complex circuitry.

• R1 = 4.7K-1/2W
• R1 = 4.7K-1/2W
• C1 = 100nF-63V
• C2 = 220µF-25V
• C3 = 220µF-25V
• C4 = 100nF-63V
• C5 = 100nF-63V
• Q1 = BD437
• Q2 = BD438
• IC1 = LM358

Discrete Virtual Ground Circuit

Here is the simple virtual ground circuit based on discrete components. This simple design comes from miniaturization guru Sijosae. Is to make a buffer from generic discrete components. The transistors can be most any complementary pair of small-signal transistors. Suitable alternatives are the PN2222A and PN2907A. The diodes are generic small-signal types. An acceptable alternative is the 1N914. This circuit has better performance than a simple resistive divider virtual ground, and the parts cost is lower than for any other circuit mentioned here. It is, however, the least accurate of the buffered virtual ground circuits.

• R1,R2 = 4.7K
• R3,R4 = 4.7R
• C1,C2 = 470uF-25V
• C3,C4 = 47uF-25V
• D1,D2 = 1N4148
• Q1 = 2SC1384
• Q2 = 2SA684
• B1 = Battery

Circuit of PSU

Switching Regulator with L4972A

The LA9472A is a 2A monolithic step down switching regulator operating in continuous mode and realized in a new BCD technology allowing the integration of isolated, vertical DMOS power transistors with mixed CMOS/bipolar transistors. The device can deliver 2A at an output voltage adjustable from 5.1V to 40V and contains diagnostic and control functions that make it particularly suitable for microprocessor based systems.

Integrated functions include a reference voltage of 5.1V at 2%, soft start, under-voltage lockout, an oscillator with feed-forward control, pulse by pulse current current limit, thermal shutdown and a reset and power failure circuit.

Telephone line monitor

This nifty little circuit lets you record your phone conversations automatically. The device connects to the phone line, your tape recorder's microphone input, and the recorder's remote control jack. It senses the voltage in the phone line and begins recording when the line drops to 5 volts or less.

• R1 270K 1/4 W Resistor
• R2 1.5K 1/4 W Resistor
• R3 68K 1/4 W Resistor
• R4 33K 1/4 W Resistor
• C1 0.22uF 150 Volt Capacitor
• Q1, Q2 2N4954 NPN Transistor
• D1 1N645 Diode
• MISC Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug

Phone Busy Indicator

This circuit may cause problems for some when used. You may want to build a different circuit.
Have you ever been using the modem or fax and someone else picks up the phone, breaking the connection? Well, this simple circuit should put an end to that. It signals that the phone is in use by lighting a red LED. When the phone is not in use, a green LED is lit. It needs no external power and can be connected anywhere on the phone line, even mounted inside the phone.

• R1 3.3K 1/4 W Resistor
• R2 33K 1/4 W Resistor
• R3 56K 1/4 W Resistor
• R4 22K 1/4 W Resistor
• R5 4.7K 1/4 W Resistor
• Q1, Q2 2N3392 NPN Transistor
• BR1 1.5 Amp 250 PIV Bridge Rectifier
• LED1 Red LED
• LED2 Green LED
• MISC Wire, Case, Phone Cord

Set/Reset Flip Flop

This is an example of a set/reset flip flop using discrete components. When power is applied, only one of the transistors will conduct causing the other to remain off. The conducting transistor can be turned off by grounding it's base through the push button which causes the collector voltage to rise and turn on the opposite transistor.

Digital Step-Km Counter

• R1,R3 22K 1/4W Resistor
• R2 2M2 1/4W Resistor
• R4 1M 1/4W Resistor
• R5,R7,R8 4K7 1/4W Resistor
• R6 47R 1/4W Resistor
• R9 1K 1/4W Resistor
• C1 47nF 63V Polyester Capacitor
• C2 100nF 63V Polyester Capacitor
• C3 10nF 63V Polyester Capacitor
• C4 10µF 25V Electrolytic Capacitor
• D1 Common-cathode 7-segment LED mini-display (Hundreds meters)
• D2 Common-cathode 7-segment LED mini-display (Kilometers)
• IC1 4093 Quad 2 input Schmitt NAND Gate IC
• IC2 4024 7 stage ripple counter IC
• IC3,IC4 4026 Decade counter with decoded 7-segment display outputs IC
• Q1,Q2 BC327 45V 800mA PNP Transistors
• P1 SPST Pushbutton (Reset)
• P2 SPST Pushbutton (Display)
• SW1 SPST Mercury Switch, called also Tilt Switch
• SW2 SPST Slider Switch (Sound on-off)
• SW3 SPST Slider Switch (Power on-off)
• BZ Piezo sounder
• B1 3V Battery (2 AA 1.5V Cells in series)

LM317 VARIABLE POWER SUPPLY

Follow all the safety precautions when working with mains voltage. Insulate all connections on the transformer.

 A truly timeless circuit. LM317 is a versatile and highly efficient 1.2-37V voltage regulator that can provide up to 1.5A of current with a large heat sink. It's ideal for just about any application. This was my first workbench power supply and I still use it. Since LM317 is protected against short-circuit, no fuse is necessary. Thanks to automatic thermal shutdown, it will turn off if heating excessively. All in all, a very powerful (and affordable!) package, indeed. Although LM317 is capable of delivering up to 37V, the circuit pictured here is limited to 25V for the sake of safety and simplicity. Any higher output voltage would require additional components and a larger heat sink. Make sure that the input voltage is at least a couple of Volts higher than the desired output. It's ok to use a trimmer if you're building a fixed-voltage supply.

Dual Polarity Power Supply

This dual polarity power supply is easy to build, requires few parts, and is adjustable from 0-15 volts. It is great for powering op amp circuits, as well as other circuits that require a dual supply voltage.

• C1, C2 2200uF 35V Electrolytic Capacitor
• C3, C4, C5, C7 1uF 35V Electrolytic Capacitor
• C6, C8 100uF 35V Electrolytic Capacitor
• R1, R4 5K Pot
• R2, R3 240 Ohm 1/4 W Resistor
• BR1 2A 30V Bridge Rectifier
• U1 LM317 Adjustable Positive Regulator
• U2 LM337 Adjustable Negative Regulator
• T1 30V Center Tapped 2 Amp Transformer
• S1 SPST 2 Amp Switch
• MISC Heatsinks For U1 And U2, Line Cord, Case, Knobs For Pots, Wire