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Other Electronic Circuits Part II

  • LASER Power Supply
    If you have ever worked with lasers, you know how fun and interesting it can be, you also know how expensive it can be. The high voltage power supplies for the laser tubes are often more expensive then the tubes themselves. This supply can be built with commmon parts, most of which you probably already have in your junk box. The secret is the transformer used. It is a common 9V 1A unit, connected backwards for step up.
  • Fantastic Atom Expander
    Here is the schematic, PC board pattern, and parts placement for a 'Fantastic Atom Expander'. This circuit produces an 'exploding atom' effect using 98 LEDs.
  • Black Light
    This circuit is a simple ultraviolate light that can be powered by a 6 volt battery.
  • Colour (Sound) Organ
    Anyone who has been to a night club, concert or school dance has probobly seen a colour organ. Colour organs cause lights to blink and flash to music from your TV, stereo, guitar and even your own voice. The colour organ presented here needs no connection to the sound source, it picks up sound from its built in microphone
  • Strobe Light *
    Disco anyone? Actually, this strobe serves a much more useful purpose then making it look cool when you dance in the dark. You can use it to view fast moving objects, look for cracks in PC boards (hold the strobe on the trace side of the board and look from the component side), and it is a great attention getter in a store window.
  • TRIAC Light Dimmer
    This little circuit can be used to dim lights up to about 350 watts. It uses a simple, standard TRIAC circuit that, in my expirience, generates very little heat. Please note that this circuit cannot be used with fluorescent lights.
  • Simple Colour Organ
    This is a simple, one lamp colour organ. It is far less complicated then the Three Channel Colour Organ (above). It is simply a lamp controlled by an SCR. It can be built in a few minutes, and combined with other circuits to make some pretty neat effects.
  • 12VDC Fluorescent Lamp Driver *
    A number of people have been unable to find the transformer needed for the Black Light project, so I looked around to see if I could find a fluorescent lamp driver that does not require any special components. I finally found one in Electronics Now. Here it is. It uses a normal 120 to 6V stepdown transformer in reverse to step 12V to about 350V to drive a lamp without the need to warm the filaments.
  • Adjustable Strobe Light
    This Adjustable Strobe Light is the bigger brother of the plain old strobe light(above). This one uses a much more powerful 'horse shoe' Xenon tube which produces more light. You can also control the flash rate up to about 20Hz. Do not look directly at the flash tube when this thing is on!
  • LASER Transmitter/Receiver
    This set of two circuits from the basis for a very simple light wave transmitter. A LASER beam is modulated and then aimed at a receiver that demodulates the signal and then presents the information (voice, data, etc..). The whole thing is very easy to build and requires no specialized parts execpt for the LASER itself.
  • 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.
  • Infa-Red Remote Control *
    This remote transmits a tone using an infa-red LED. This tone is decoded by the receiver. Since the receiver only switches when it hears the tone, there are no accidental activations.
  • LED Chaser *
    I don't know why, but people like blinking lights. You see LED chasers everywhere, in TV shows (Knight Rider), movies, and store windows. This schematic is my version of a simple 10 LED chaser. There is no 555 timer used because at my local electronics store they are over $4 Cdn. Instead, an oscillator is made up of two sections of a 4011 NAND gate is employed. This chip is very inexpensive and extremely common.
  • Flash Slave Trigger *
    Flash slaves are used when you need to supplement one flash unit with one or several more. This slave trigger simply triggers those other units. It does this by "seeing" the first flash (using a phototransistor) and triggering the other flashes a few microseconds later. The sensitivity of the circuit is adjustable to compensate for ambient light or dimmer than usual master flashes.
  • 40W Fluorescent Lamp Inverter
    This 40W fluorescent lamp inverter allows you to run 40W fluorescent tubes from any 12V source capable of delivering 3A. This is basically a larger version of the 12VDC Fluorescent Lamp Driver and can be used to light regular or blacklight tubes.
  • 3 Channel Spectrum Analyzer
    This 3 channel 15 LED spectrum analyzer is the perfect addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range. The circuit will take line level output from most any audio source, and operates on 12V DC. This means that it can even be run in a car.
  • 8 Watt Audio Amp *
    Here is the schematic for an 8 watt audio amp. This amp can be used as a simple booster, the heart of a more complicated amplifier or used as a guitar amp.
  • FM Transmitter
    Here is the schematic, PC board pattern, and parts placement for a low powered FM transmitter. The range of the transmitter when running at 9V is about 300 feet. Running it from 12V increases the range to about 400 feet. This transmitter should not be used as a room or telephone bug.
  • Op Amp Radio *
    Here is a simple radio that is easy to build and inexpensive. In fact, you probobly have all the parts you need in your junk box. You'll be suprised at the great reception with this little set.
  • FET Audio Mixer
    This simple circuit mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consumes very little power. The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "sections" which are clearly visible on the schematic.
  • Transistor Organ
    This simple circuit can provide hours of enjoyment as you learn tunes, play duets or just make some really weird sounds by pushing all the buttons at once. You have probably seen this ciruit before, it is fairly common. I have seen it in several books. The best thing about the circuit is that you can tune each individual note, or go to a whole new octive by changing one capacitor (C1). Because of this, it is possible to from an entire Transistor Organ ensemble. Why you would want to do this is anyone's guess...
  • 50 Watt Amplifier
    This is a handy, easy to build general purpose 50 watt amp. The amp has an input for a radio, TV, stereo or other line level device. It also has a phono input for a record player, guitar, microphone or other un-amplified source. With the addition of a low pass filter at the input, it makes a great amp for a small subwoofer.
  • 8 Note Tune Player *
    This neat little circuit can play 8 note tunes at any speed you want. You select the notes with 8 trim pots. The speed in selected through a ninth pot. The circuit draws very little power and can be powered by a 9 volt battery, with the addition of a 7805 regulator to power the TTL logic used.
  • 22 Watt Audio Amplifier
    The 22 watt amp is easy to build, and very inexpensive. The circuit can be used as a booster in a car audio system, an amp for satellite speakers in a surround sound or home theater system, or as an amp for computer speakers. The circuit is quite compact and uses only about 60 watts. The circuit is not mine, it came from Popular Electronics.
  • Crystal Radio *
    I have received a number of emails regarding schematics for crystal radios. After about the third email, I figured that I may as well put one on my page. So here it is. The circuit is very simple with only 5 parts, but performs very nicely when used with the right size antenna.
  • Digital Volume Control *
    This digital volume control has no pot to wear out and introduces almost no noise in the circuit. Instead, the volume is controlled by pressing UP and DOWN buttons. This simple circuit would be a great touch to any home audio project.
  • Sound Level Meter *
    This nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components. This circuit can also be integrated into audio amp projects.
  • 3 Watt FM Transmitter (Rae XL Tkacik) *
    This is the schematic for an FM transmitter with 3 to 3.5 W output power that can be used between 90 and 110 MHz. Although the stability isn't so bad, a PLL can be used on this circuit.
  • Microphone Mixer (Anatoly I. Shikhatov) *
    This relatively simple mixer was designed for three dynamic microphones, but can be re-designed for more or less. Level and tone controls are available to tailor the sound to your needs.
  • Tone Control
    This simple tone control can be used in may audio applications. It can be added to amplifers, used as a stand alone control module, or even built into new and exciting instruments. It's one IC construction makes it a very compact circuit, as only a few support components are required. Plus, it does not use a dual power supply. This means that the circuit will run from 9V to 15V (although the bass will be a little weak at 9V). The circuit is by Robert Barg and originally appeared in the Think Tank column of the May 1998 issue of Popular Electronics..
  • Guitar Fuzz Effect *
    Fuzz is one of the classic guitar effects, and this simple circuit generates it quite well. The circuit is so compact that it can be built into guitars or amps that do not have built in fuzz to add that capability to the instrument. The circuit does not use much battery power, so a standard alkaline battery will last many years even with daily use.
  • Stereo Tube Amplifier (Weslee Kinsler) *
    The circuit is simple, yet is capable of excellent performance. I designed it specifically for use as an amplifier for the digital sound card in my computer. Audio input can be from any two-channel line level device such as a television, CD player, or VCR. It is of the tube type, using only 5 tubes total with no more than about 45 Watts power consumption from the outlet. It uses 3 types of tube 1 5Y3 GT vacuum rectifier, 2 6SF5 GT high-mu triodes, and 2 6K6 power beam amplifiers. These are all full-size octal type tubes which are commonly available today for between $3-5 each.
  • Electronic Stethoscope *
    Stethoscopes are not only useful for doctors, but home mechanics, exterminators, spying and any number of other uses. Standard stethoscopes provide no amplification which limits their use. This circuit uses op-amps to greatly amplify a standard stethoscope, and includes a low pass filter to remove background noise.
  • Power Supply *
    When working with electronics, you always need one basic thing; power. This power supply is great for powering all kinds of electronic projects. It produces a well filtered, variable 1.2-30 volts at 5 amps. It is easy to build and the parts are realitively easy to find.
  • LASER Power Supply
    If you have ever worked with lasers, you know how fun and interesting it can be, you also know how expensive it can be. The high voltage power supplies for the laser tubes are often more expensive then the tubes themselves. This supply can be built with commmon parts, most of which you probably already have in your junk box. The secret is the transformer used. It is a common 9V 1A unit, connected backwards for step up.
  • Solid State Tesla Coil/High Voltage Generator
    This is a fun and useful circuit for demonstrating high frequency high voltge. It can produce up to about 30KV, depending on the transformer used. It is cheap and easy to make, thanks to the standard TV flyback transformer used. It can power LASERS (although I have never tried), demonstrate St.Elmo's fire, and even cause a fluorescent bulb to light from as much as 2 feet away.
  • 12VDC To 120VAC Inverter
    Have you ever wanted to run a TV, stereo or other appliance while on the road or camping? Well, this inverter should solve that problem. It takes 12 VDC and steps it up to 120 VAC. The wattage depends on which tansistors you use for Q1 and Q2, as well as how "big" a transformer you use for T1. The inverter can be constructed to supply anywhere from 1 to 1000 (1 KW) watts.
  • Portable CD Player Adapter For Car *
    Whenever I'm in the car listening to my favourite CD, it always happens-my batteries go dead. To solve that problem, I built this extremely simple regulator circuit. It steps down the 12V from the lighter socket to 9V which is used by the CD player. Different CD players (I have a Sony Discman) may require different voltages, so just use the correct regulator. All the 78xx series regulators have the same pin out, so the circuit is universal.
  • 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.
  • High Current Power Supply *
    Since my page was first posted, I have received a number of emails asking about a high current power supply. I looked around, but couldn't find one that was suitable. So, I designed this. It is a linear supply, which might have a few of you rolling your eyes, but it takes very few parts, is simple to build and can supply huge currents.
  • Car Battery Charger *
    This charger will quickly and easily charge most any lead acid battery. The charger delivers full current until the current drawn by the battery falls to 150 mA. At this time, a lower voltage is applied to finish off and keep from over charging. When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished.
  • High Voltage High Current Power Supply * *
    A while ago I came up with the idea of using a microwave transformer as a high voltage, high current power supply. Even though I had no use for such a supply, I decided to design one anyway. This is a very simple design. Note: I have not built this supply becasue I have no use for it. If you build this supply without knowledge in electronics or high voltage, you have basically signed your own death certificate. This supply can be very dangerous if not treated properly. DO NOT BUILD THIS SUPPLY UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING! I assume no responsibility for any damages or injuries caused by this supply.
  • Transformerless Power Supply *
    I have received a few emails asking for a transformerless power supply. Here is such a supply. This supply uses no heavy step down transformer and has an extremely low parts count. The circuit can be built very small and can supply small currents for small projects. The major downfall of this supply is that it is not isolated from the AC line and can only supply small currents.
  • Voltage Inverter *
    This simple circuit is a good solution to the powering a dual supply op amp from a single battery problem. The circuit simply takes a positive voltage and inverts it. It uses only one 555 timer and a few other passive components, so it doesn't add much in the way of size and cost to a project.
  • Fixed Voltage Power Supply *
    The fixed voltage power supply is useful in applications where an adjustable output is not required. This supply is simple, but very flexable as the voltage it outputs is dependant only on the regulator and transformer you choose. The maximum output current is 1.5A.
  • Voltage Inverter II *
    This simple and inexpensive circuit can produce a dual (positive and negative) voltage from a single supply input. It is therefore extremely useful for powering opamp and other circuits that require a dual voltage from a single battery. The circuit will operate at an input voltage from around 5V to 20V and produce a output from +-2.5V to +-10V.
  • 6V to 12V Converter *
    This inverter circuit can provide up to 800mA of 12V power from a 6V supply. For example, you could run 12V car accessories in a 6V (British?) car. The circuit is simple, about 75% efficient and quite useful. By changing just a few components, you can also modify it for different voltages.

  • Wireless Auto Tachometer
    Anyone performing their own automobile tune-ups knows how important it is to know your engines speed. With this tachometer, you can measure your engines speed without any connections or annoying timing lights.
  • Automatic Headlight Brightness Switch * NEW!
    Driving the highway with your high-beam headlights can really increase your visibility, but can he a blinding hazard for other drivers. This simple circuit can be wired into your headlight switch to provide automatic switching between high and low beam headlights when there is oncoming traffic. It does this by sensing the lights of that traffic. In this way, you can drive safely with your high-beams on without blinding other drivers.
  • Parallel (Printer) Port Interface
    This is the basic interface I used as part of my Computerized Room project. This is the parallel interface only. The 8 bit input card can be found, along with the rest of the project, at Computerize Your Room/House. This interface, as well as the other two interfaces, came from the book "The Robot Builders Bonanza", by Gordan McComb. This interface is also useful for controlling small robots, etc. It is cheap and fairly easy to build, although you should not attempt this project unless you have prior experience with electronics. You probably won't damage anything if you hook it up wrong, but there is always a chance (some parallel ports are better protected then others). If possible, test the project on someone else's, or a school computer :-)
  • Phone Busy Indicator *
    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.
  • Cut Phone Line Detector *
    A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn't take me long to find this circuit in Electronics Now. When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system.
  • Telephone Hold Button
    Although a hold feature is standard on most new phones, a lot of us still use the origional bell phones. Those of us that require a hold feature will find this circuit very useful. It is easy to build, and is compact enough to be installed inside the phone with no real problem. It is also powered by the phone line itself, eliminating the need for batteries.
  • Telephone Recorder *
    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.
  • FM Telephone Bug
    Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio. The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet. It is extremely easy to build and is therefore a good, useful beginner project.
  • Simple Phone Tap (Derek Tombrello) *
    This circuit is extremely simple, therefore there is less chance of any problems. It can be placed anywhere on the phone line and it will record any conversation on any phone on that line.
  • Ringing Phone Light Flasher * *
    I have gotten several emails asking how to connect up some lights so that when the phone rings, they flash. This is very useful in a situation were there is lots of noise and it is impossable to hear the phone, such as a workshop. Here is such a device. The ring detect part of this circuit came from http://www.hut.fi/Misc/Electronics/circuits/telephone_ringer.html.
  • Computerize Your Room/Home *
    So you've read about my Computerized Room or have seen those nifty home automation products advertised in the back of electronics magazines? Or perhaps someone you know has done something similar. At any rate, you have decided to try it yourself. The first thing I will say, however is that it is not cheap.
  • Simple Lie Detector
    Here's a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It is not as sophisticated as the ones the professionals use, but it works. It works by measuring skin resistance, which goes down when you lie.
  • Rain Detector *
    This circuit uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.
  • Stepper Motor Controller *
    I found this circuit in my files. I don't know where it came from, but it looks like I photocopied it from somewhere years ago. I have been told that it came from "The Robot Builder's Bonanza", by Gordan McComb. Anyway, I thought that it should be fairly useful, so I decided to post it here. The circuit is very simple and inexpensive. This is good thing because most commercial stepper motor controller ICs are quite expensive. This circuit is built from standard components and can easily be adapted to be controlled by a computer. If you use cheap surplus transistors and stepper motor, the price of the circuit can be kept to under $10.
  • Pulse Width Modulation DC Motor Control *
    Often, people attempt to control DC motors with a variable resistor or variable resistor connected to a transistor. While the latter approach works well, it generates heat and hence wastes power. This simple pulse width modulation DC motor control eliminates these problems. It controls the motor speed by driving the motor with short pulses. These pulses vary in duration to change the speed of the motor. The longer the pulses, the faster the motor turns, and vice versa.
  • Touch Switch *
    A touch switch is a switch that is turned on and off by touching a wire contact, instead of flicking a lever like a regular switch. Touch switches have no mechanical parts to wear out, so they last a lot longer than regular switches. Touch switches can be used in places where regular switches would not last, such as wet or very dusty areas.
  • 7 Segment LED Counter *
    This simple counter can be used to count pulses, as the basis for a customer counter (like you see at the doors of some stores), or for anything else that may be counted. The circuit accepts any TTL compatible logic signal, and can be expanded easily (see Notes).
  • Time Delay Relay
    A time delay relay is a relay that stays on for a certain amount of time once activated. This time delay relay is made up of a simple adjustable timer circuit which controls the actual relay. The time is adjustable from 0 to about 20 seconds with the parts specified. The current capacity of the circuit is only limited by what kind of relay you decide to use.
  • Pine Racecar Victory Judge *
    I have received countless emails asking for a circuit to tell the user which car won in a pine car (also called Pinewood Derby, Cub Car, Scout Car, etc.) race. This simple circuit takes care of the guesswork, lighting the appropriate LED to indicate the winner.
  • Time Delay Relay II (jawaharlal@excite.com) *
    When activated by pressing a button, this time delay relay will activate a load after a specified amount of time. This time is adjustable to whatever you want simply by changng the value of a resistor and/or capacitor. The current capacity of the circuit is only limited by what kind of relay you decide to use.
  • Simple Polarity Tester (Dudley LeRoux) *
    This tester can be used to check the polarity of any power source, and is therefore very useful when installing automotive equipment, alarm systems or anything else you can think of. Because this circuit is so simple and cheap, even frying one with an over voltage is not a big deal.
  • Wire Loop Alarm (Alex Meaden) *
    This circuit is a simple wire loop alarm that can be used in doorways, hallways, or any other place the tripwire will be broken by intruders. The circuit has a built in siren, but it can be replaced by a relay to drive an external siren, commercial alarm, etc.
  • IR Remote Jammer (Carl) * NEW!
    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.
  • Video Activated Relay *
    This simple circuit from the May 1996 Think Tank column of Pupular Electronics activates a relay when it senses a composite video signal. This allows you to use the tuner built into your VCR to turn on and off older TVs that are not equipped with a remote. It can also be used to activate surround sound equipment, turn off the room lights, turn on video game consoles, etc. For such a simple circuit, it is very versitile.
  • Air Flow Detector *
    This simple circuit uses an incandescent lamp to detect airflow. With the filament exposed to air, a constant current source is used to slightly heat the filament. As it is heated, the resistance increases. As air flows over the filament it cools down, thus lowering it's resistance. A comparator is used to detect this difference and light an LED. With a few changes, the circuit can be connected to a meter or ADC to provide an estimation on the amount of air flow.
  • Low Voltage Alarm *
    This low voltage circuit can be used to monitor batteries and other volatile sources of current for problems. The circuit sounds an alarm and lights an LED, but can be interfaced to any number of other circuits for many different uses.an be connected to a meter or ADC to provide an estimation on the amount of air flow.