Top Circuits Page 232
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48 V phantom` powering has become the standard for professional condenser microphones. The supply (or rather bias) voltage is applied over both wires of the balanced screened cable via two 6k8 resistors (see reference [1]) the absolute value is not critical,....
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This solid-state push-pull single-ended Class A circuit is capable of providing a sound comparable to those valve amplifiers, delivering more output power (6. 9W measured across a 8 Ohm loudspeaker cabinet load), less THD, higher input sensitivity and better....
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A radio camera on a model railway should transmit constantly while the train is moving and continue transmitting for a few minutes after the train stops. But if the train starts up again after a relatively long halt, imagery should be transmitted....
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This circuit is a small +5V power supply, which is useful when experimenting with digital electronics. Small inexpensive wall tranformers with variable output voltage are available from any electronics shop and supermarket. Those transformers are easily....
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The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in....
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This design adopts a well established circuit topology for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the very simple circuitry, even for comparatively....
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This small amplifier is constructed around the TDA2003 IC, capable of delivering 4Wrms at 4ohms. The TDA 2003 has improved performance with the same pin configuration as the TDA 2002. The additional features of TDA 2002, very low number of external....
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This circuit lets an external 12V SLA battery power a camcorder which normally has an inbuilt 7. 2V battery. Such batteries can now be very difficult or expensive to obtain for earlier model camcorders. In essence, the circuit is a standard LM317 adjustable....
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The voltage regulators from the 78xx-series are found in many analogue power supplies. It seems, then, somewhat super‚uous to say much more about them. But on the other hand, it can be very useful to highlight the important points, just because they are so....
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A difficult problem in the design of conventional stereo tone controls is obtaining synchronous travel of the potentiometers. Even a slight error in synchrony can cause phase and amplitude differences between the two channels. Moreover, linear potentiometers....
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This acoustic sensor was originally developed for an industrial application (monitoring a siren), but will also find many domestic applications. Note that the sensor is designed with safety of operation as the top priority: this means that if it fails then....
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Short-wave listeners often are not able to, or allowed to, install a long-wire antenna or other large dimension antenna in or around the home. In such cases, the present active antenna, intended for the frequency range 3 30 MHz, may be found useful. The....
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This current-limiting circuit, shown in this example as part of a small bench power supply, could in principle be used in conjunction with any dual-rail current source. The part of the circuit to the left of the diagram limits the current at the input to the....
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AFX slot car sets are very enjoyable but you can increase the fun with a lap counter. This circuit will count from 00 to 99, with independent counters for each track. The sensing device used is a Hall effect sensor (UGN3503; available from Dick Smith....
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This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least. Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared....
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Here is an idea for a simple low-cost adaptor that allows a portable FM radio (or MP3 player with FM tuner) to be connected to an external antenna and to audio equipment such as a hifi system or PC sound card. Portable FM radios and some MP3 players....
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If you`re a biker or scooter rider you`ll know how easy it is to forget to cancel your flashing indicators after turning without an audible reminder. Constantly glancing at indicator lamps is hardly an option; your eyes should be on the road ahead! The....
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This circuit was intended to be used as a separate, portable unit, to signal by means of a LED when the output wave form of a particular audio stage is "clipping" i. e. is reaching the onset of its maximum permitted peak-to-peak voltage value before an....
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This simple circuit indicates the amount of power that goes to a loudspeaker. The dual-color LED shows green at an applied power level of about 1 watt. At 1. 5 watts it glows orange and above 3 watts it is bright red. The circuit is connected in parallel....
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Do you drive an older car without an automatic "lights-on" warning circuit If so, you`ve probably accidentally left the lights on and flattened the battery on one or more occasions. This headlights reminder circuit will prevent that. It`s more complicated....
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Voltage regulator ICs (78xx series) provide a steady output voltage, as against a widely fluctuating input supply, when the common terminal is grounded. Any voltage about zero volt (ground) connected in the common terminal is added to the output voltage.....
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In many cases, the dimmer presented here may be built into a wall-mounted box containing the light switch. It is intended for use with 240 V incandescent lamps only. When it is fitted, and the light is switched on, the lamp does not come on fully for about....
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New applications for DC voltage converters, such as the workhorse` LT1070, arise every day. These converters can be adapted to nearly every imaginable ratio of input and output voltages. However, all of these circuits and devices have the same shortcoming,....
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Most, if not all, recent cars have an impressive amount of electronics, whether it be ABS brake systems, engine control with injection calculators, airbag activation, or other various functions, called comfort functions. Among them is one which we tend to....
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A useful timing strobe can be constructed using high-brightness LEDs and a few common components. Ignition pulses from the number 1 cylinder high-tension lead are used to trigger the circuit via a home-made inductive pickup. Transistors Q1 & Q2 buffer and....
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There are a few situations when a power failure is particularly difficult to handle. Some of these circumstances occur in the bathroom. This little circuit will pay for itself many times over the first time it is used, especially if you are in the shower.....
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Most off-the-shelf car battery chargers cannot not be left connected to the battery for long periods of time as over-charging and consequent battery damage will occur. This add-on circuit is placed in series with the battery being charged and is powered by....
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Your child`s battery toy has failed and you have to fix it. Once you have managed to get it apart, the battery compartment is not likely to be connected to the works or the batteries might have gone flat anyway. The solution is this switchable supply which....
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Is the battery empty, or is there something wrong with the device That`s always a difficult question when your walkman or some other battery-powered device appears to be dead when you switch it on. Before you take it to the shop for servicing, the first....
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Many blind and deaf-blind persons use portable electronic devices to assist their everyday lives but it is difficult for them to test the batteries used in this equipment. Talking voltmeters are available but there is no equivalent usable by deaf-blind....
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This circuit is presented as an alternative to the IR beam break detector featured in the June 2009 issue (Silicon Chip). In order to make it relatively insensitive to ambient light, it uses a standard IR receiver IC such as the Jaycar ZD-1942. This has a....
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This circuit generates a dual-tone bells ringing similar to most door-bell units. It can be used in many applications other than door-bell. In the Notes below several options will be given in order to suit different needs. The circuit as shown in the diagram....
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The idea for this circuit came when the author had problems with the wireless speedometer on his bicycle. Such a device consists of two parts: the cycle computer itself and a transmitter that is mounted on the front fork. A small magnet is attached to the....
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This circuit represents a somewhat unusual blinker indicator for use in a car or model. The running-light display progresses toward the left or the right depending on which directional signal is activated. That`s pretty cool if you`re fond of light-show....
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Firstly, it demonstrates how the combination of a blue and a white LED can be used to give a realistic imitation of a camera flashlight. Secondly, the good old 555 IC is used in a way many of you may never have seen before alternately mono-stable / astable....
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It is well known that through such simple everyday activities as walking on a carpet or moving in a chair, the body accumulates a static charge - sometimes many thousands of volts. Due to its extreme sensitivity, this circuit will detect not only such....
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This circuit could be used (depending on your circumstances) by a gentleman to summon his butler, a manager his secretary or as in the author`s case to call the kids down to dinner without having to shout above the level of the CD player/TV/games console in....
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Going camping nowadays involves taking lots of electronic equipment whether for day to day running or for fun and entertainment. Most of the time a charged lead acid battery and a power inverter would be used to ensure a smoothly organized holiday where....
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A car battery deteriorates in use and its life seldom exceeds four years. When new, its voltage may drop to only 2V while cranking the engine. As the battery ages, its internal impedance increases and so the voltage drop while cranking also increases, until....
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This device is a simple timer, allowing to keep on the headlights of your vehicle for about 1min. and 30sec. , e. g. when accessing some dark place, without the necessity of coming back to switch-off the lights. Pushing on P1 allows C1 charging to full 12V....
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Most cars do not have delayed interior lights. The circuit presented can put this right. It switches the interior lights of a car on and off gradually. This makes it a lot easier, for instance, to find the ignition keyhole when the lights have gone off after....
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Nowadays, just about every house has an outside lamp with a motion sensor. Such a device eliminates the need to feel your way to the front door, and it apparently also scares away intruders. The only problem is that free-running dogs and cats in the....
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Even though today`s electrical appliances are increasingly often self-powered, especially the portable ones you carry around when camping or holidaying in summer, you do still sometimes need a source of 230 V AC - and while we`re about it, why not at a....
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The easy way to measure high AC currents is to use a clamp meter but these are generally quite expensive and cost several hundred dollars at a minimum. Add-on clampmeter adaptors can work well but they only work with digital multimeters which have millivolt....
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By using a simple visual indicating system, this small transistor tester allows you to run a quick go/non-go` check on NPN as well as PNP transistors. If the device under test is a working NPN then the green LED (D1) will‚ash, while the red counterpart....
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This simple but effective circuit can be used to control water level in a container. The prototype is used to pump water out of a bucket that collects condensation from a home air-conditioning system. The design is based around a 555 timer (IC1). Although....
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This circuit can switch two or more devices on and off in response to a series of rapid handclaps. The claps are picked up by an electret microphone and amplified by a 741 op amp (IC1). IC1 is configured as an inverting amplifier, with its gain and hence the....
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This project consists of a small, portable DJ mixer powered by a 9V dc external supply adaptor or from a 9V PP3 battery. The mixer features two stereo phono inputs and two stereo line-level inputs and has one stereo mixing channel. A microphone input and a....
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Amplifiers which run from 12V DC generally don`t put out much power and they are usually not hifi as well. But this little stereo amplifier ticks the power and low distortion boxes. With a 14. 4V supply, it will deliver 20 watts per channel into 4-ohm loads....
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The compact, low-cost condenser mic audio amplifier described here provides good-quality audio of 0. 5 watts at 4. 5 volts. It can be used as part of intercoms, walkie-talkies, low-power transmitters, and packet radio receivers. Transistors T1 and T2 form....
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This simple circuit uses a 741 op-amp in differential mode as a continuity tester. The voltage difference between the non-inverting and inverting inputs is amplified by the full open loop gain of the op-amp. Ignore the 470k and the 10k control for the....
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Most LED driver circuits use a series resistor to control the current through the LED. For applications needing a few LEDs, this is optimal. However, for applications needing many LEDs, this becomes extravagantly inefficient and it is tempting to keep the....
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The adjustment control for the contrast of an LC-Display is typically a 10-k potentiometer. This works fine, provided that the power supply voltage is constant. If this is not the case (for example, with a battery power supply) then the potentiometer has to....
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In essence, this circuit is a 15 to 20-second courtesy light extender for cars. It is activated in the usual way by opening a door but it also samples the negative lock/unlock signals from a car alarm or central locking and does two more things. First, when....
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Owing to the recent launching in Europe of Cranial Electrotherapy Stimulation (CES) portable sets, we have been "Electronically Stimulated" in designing a similar circuit for the sake of hobbyists. CES is the most popular technique for electrically boosting....
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This circuit generates a two-tone effect very much alike the cuckoo song. It can be used for door-bells or other purposes thanks to a built-in audio amplifier and loudspeaker. Used as a sound effect generator it can be connected to external amplifiers, tape....
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The basic circuit illuminates up to ten LEDs in sequence, following the rhythm of music or speech picked-up by a small microphone. The expanded version can drive up to ten strips, formed by up to five LEDs each, at 9V supply. IC1A amplifies about 100 times....
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A popular project among microcontroller aficionados is to build a radio-controlled clock. Tiny receiver boards are available, with a pre-adjusted ferrite antenna, that receive and demodulate the DCF77 time signal broadcast from Mainf lingen in Germany. DCF77....
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Every self-respecting DIYer makes his own electronic dice with LEDs as spots. Then you don`t have to throw the dice anymore just push the button. The electronics also ensures that nobody can try to improve his luck by fiddling with the dice. Too bad for sore....
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This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor`s output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the....
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This circuit shows that dimmers intended for use at mains voltage do not always have to contain a triac. Here, a MOSFET (BUZ41A, 500 V/4. 5A) in a diode bridge is used to control the voltage across an incandescent bulb with pulse-width modulation (PWM). A....
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PWM waveforms are commonly used to control the speed of DC motors. The mark/space ratio of the digital wave-form can be defined either by using an adjustable analogue voltage level (in the case of a NE555 based PWM generator) or digitally using binary....
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This simple robot, which responds to light and avoids obstacles, can be built without using a microcontroller, programmer or PC. The only special` component in the circuit is a window discriminator (a fancy version of a window comparator). Resistors R1 and....
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The circuit in the diagram enables a negative voltage to be derived without the use of integrated circuits. Instead, it uses five n-p-n transistors that are driven by a 1 kHz (approx) TTL clock. When the clock input is high, transistors T1 and T2 link....
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Sometimes you have to do it the hard way, even if doing it the easy way is an option. That is the case here. The intention is to add a second doorbell in parallel with the existing bell. This does not, in principle, require any electronic components. You....
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If you`re expecting an important visitor but you just have to step out for a moment, an electronic doorbell memory can come in handy so you can see whether someone rang while you were out. Of course, you can`t tell whether it was the visitor you were....
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This circuit takes two separate line-level stereo (L & R) signals and combines them into one stereo (L & R) output, thus avoiding the need to switch between two pairs of input signals. In the author`s application, it is used to feed the stereo audio from a....
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The security of many electrical devices depends today on the availability of an earthed mains outlet. We should remember that these are connected to the frame or to the metal housing of the equipment and so it routes to the protective earth (PE) connections.....
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This LED lamp was originally designed for use on a budget solar-charged 12V electrical system. It is bright enough for comfortable reading at night and features constant LED brightness with diminishing battery voltage. The circuit uses six high-brightness....
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A partial solution to quietening noisy PCs can be to reduce the speed of internal cooling fans. Low-cost fan speed controllers are available, but they often employ inefficient, heat-generating linear regulators and contain no temperature feedback mechanism.....
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This egg timer, which is both simple and functional, shows once again that it is not essential to use a microcontroller for everything these days. The circuit consists of only two ICs from the standard 4000 logic family, a multi-position rotary switch and a....
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This simple circuit can start small (15W or less) fluorescent tubes such as those used in PC board exposure and EPROM ultraviolet erasure boxes. As you can see, the tube`s filament heaters are not used. Instead, ignition is provided by a voltage tripler....
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An EL lamp is a solid state, low power, uniform area light source. Because of its thin prole (as thin as 0. 3 mm) and the fact that it can be built into almost any size and shape, EL lamps are an ideal way to provide back-lighting for LCD displays, membrane....
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Here is the circuit diagram of a guitar preamplifier that would accept any standard guitar pickup. It is also versatile in that it has two signal outputs. A typical example of using a pick-up attached to a guitar headstock is shown in Fig. 1. The pickup....
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The simplicity of a traditional die makes it exceptionally difficult to create a fully equivalent electronic version, if only because an electronic version requires a power supply and a collection of electronic components that occupy a much larger volume....
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This circuit produces a ringing sound similar to that made by more recent telephones. It consists of three almost identical oscillators connected in a chain, each generating a squarewave signal. The frequency of each oscillator depends on the RC combination:....
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Although it does not have the same charm as real mercury barometers with long glass tubes on pieces of carved and polished wood, the Torricelli barometer discussed here is a functional equivalent and electronic replica of the Torricelli barometer. Actually,....
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Mechanical contacts have the disadvantage that they wear out. That is why it is practical to use an electronic touch switch` in some situations. With such a touch switch the resistance of the human skin is used for the switching action. The schematic shows....
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This sensitive circuit is basically a comparator, detecting very slight temperature changes in respect to the ambient temperature. It was primarily intended to detect draughts around doors and windows that cause energy leaks but can be used in many other....
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As electrolytic capacitors age, their internal resistance, also known as "equivalent series resistance" (ESR), gradually increases. This can eventually lead to equipment failure. Using this design, you can measure the ESR of suspect capacitors as well as....
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This circuit substitutes two white Luxeon 1W Star LEDs for the inverter and fluorescent tube in a standard battery-backed illuminated exit sign, as used in commercial premises. While the Luxeons have less light output than a standard small fluorescent tube,....
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Using this design, you can construct an electromagnetically impulsed pendulum clock with a 1-second beat. On the prototype, the pendulum rod is 115cm long with a bob adjusted to make it beat every second. It is suspended on a short piece of mainspring from a....
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The current source in the diagram, which react very fast to changes in the input signal, may be used, for instance, in certain measurements. Differential amplifier IC1 ensures that the potential across R2 is equal to the input voltage: Iout =Uin/R2. The....
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Regardless of whether you want to effectively imitate a house fire, a campfire, or light from welding, the circuit described here fills the bill without using a microcontroller, although it does use a larger number of components (including some truly....
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Using just two NAND or inverter gates its possible to build a D type (or toggle`)‚ip-‚op with a push-button input. At power-up the output of gate N2 is at a logical 1`, ensuring that transistor T2 is switched off. When the push-button is pressed the output....
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Although not a new device, the LM317 is still a high-performance regulator. Its output voltage is essentially immune to fluctuations in load, supply voltage and temperature and this makes it ideal as the central element in a float charger for NiMH cells.....
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Most commercial DVM modules with an LCD readout are 9-V powered and based on an ICL7106 or similar A-D converter chip. These modules are typically used in laboratory power supplies and other test and measurement equipment where a drop-in solution needs to be....
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Here is a very simple, inexpensive and interesting project which provides lot of fun to a home experimenter or hobbyist. This simple transmitter can transmit speech over a short range. It can be used as a simple cordless microphone. The circuit uses two....
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For several years now, a rear fog lamp has been mandatory for trailers and caravans in order to improve visibility under foggy conditions. When this fog lamp is switched on, the fog lamp of the pulling vehicle must be switched of to avoid irritating....
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In most countries it is now mandatory or at least recommended to have a rear fog light on a trailer with the additional requirement that, when the trailer is coupled to the car, the rear fog light of the towing car has to be off. The circuit shown here is....
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This circuit enables you to display four signals simultaneously using only one channel of your oscilloscope. Essentially, it switches each of the inputs through to the output in turn, with some signal massaging in between. As shown, it is suitable only for....
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This module can be a necessary addition to the Modular Preamplifier Control Center when more than two sources need to be connected to the preamplifier chain. Four high level inputs can be selected by means of SW1 and routed to the output. The output of this....
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The main purpose of this design was to obviate a small defect of the very popular Fridge Door Alarm circuit, available on this website since 1999 and built by a lot of hobbyists. Unfortunately, that circuit stops operating when the battery voltage falls....
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This design allows to operate two intercom stations leaving the operator free of using his/her hands in some other occupation, thus avoiding the usual "push-to-talk" operation mode. No complex changeover switching is required: the two units are connected....
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The charging circuit stops automatically when the battery is fully charged. So you can leave the emergency light connected to AC mains overnight without any fear. The circuit can be divided into inverter and charger sections. The inverter section is built....
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This circuit will be particularly useful to those hobbyists who use a breadboard` to try out ideas and who also use a simple home-made` DC power supply consisting of a transformer, rectifier, smoothing capacitor and protective fuse, that is, one without over....
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Sometimes the need arises for a simple, gated, pulsed alarm. The circuit shown here employs just four components and a piezo sounder and is unlikely to be out-done for simplicity. While it does not offer the most powerful output, it is likely to be adequate....