Top Circuits Page 195
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The design of solar panel systems with a (lead-acid) buffer battery is normally such that the battery is charged even when there is not much sunshine. Thi....
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First I bought another front wheel, one which has a dynamo already built in the hub. This supplied a nice sine wave of 30 Vpp (at no load). With this knowledge I designed a simple power supply. The transistors that are used are type BD911. These are a bit of....
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The idea behind this economical ?ashing LED indicator is very simple: it uses a very low frequency oscillator to drive two LEDs. As can be seen in the cir....
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The consumer unit (or electricity meter`) cupboard in some older houses is a badly lit place. If the bell transformer is also located in this cupboard, it may be used to provide emergency lighting by two high-current LEDs. These diodes are powered via a....
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Ideal to operate 3 to 24V DC existing on-circuit lamps This circuit was designed to provide that continuous light lamps already wired into a circuit, beco....
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Common to all the devices is that they emit intense red light with a wavelength of 660 nm. Some biophysicists claim that light of this wavelength can have a positive effect on the human body and can initiate healing processes. This so-called phototherapy` is....
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Before you use LEDs, it`s a good idea to check them out. With a LED tester, you can even do it in the dark! LEDs are available nowadays in all shapes and colors. There are types with clear, colorless packages, while others have colored plastic packages. Many....
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This simple LED torch is driven by a 2-transistor blocking oscillator which steps up the voltage from a 1.5V cell. It relies on the inherent current limit....
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This circuit was constructed to control the pump in a garden pond, so that it automatically turns on at dawn and off again at dusk. Not only does this mea....
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The circuit described here counts the number of times that an infrared beam is interrupted. It could be used to count the number of people entering a room, for instance, or how often a ball or another object passes through an opening (handy for playing....
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This Line Following Robot sensor or surface scanner for robots is a very simple, stamp-sized, short range (5-10mm) Infrared proximity detector wired aroun....
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The National Semiconductor LMV225 is a linear RF power meter IC in an SMD package. It can be used over the frequency range of 450 MHz to 2000 MHz and requ....
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A segment may be tested by applying an alternating voltage of a few volts across it. Note that the application of a direct voltage will damage the display irreversibly: the resulting current will remove the tracks. The alternating voltage should contain not....
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This circuit was developed to charge the Lithium-Polymer cells used in a model aircraft. Lithium-Polymer cells are incredibly lightweight compared to Ni-c....
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A simple 5 Volt regulated PSU featuring overvoltage protection. The 5 volt regulated power supply for TTL and 74LS series integrated circuits, has to be v....
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This timer was designed mainly to switch off a portable radio after some time: in this way, one can fall asleep on the sand or on a hammock, resting assured that the receiver will switch off automatically after some time, saving battery costs. R1 and C1....
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This design combines power-on and low-battery indication, can operate with any battery voltage up to 15V, has very low current drain (2mA or less) and cos....
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This low-cost burglar alarm employs a 12V strobe light and a truck reversing horn as the visible and audible alarm outputs while the alarm itself is a 12V....
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This simple dual digital dice is based on three low-cost ICs, a few transistors and a handful of LEDs. IC1a & IC1b operate as an oscillator with a frequen....
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Low cost solution for charging of both NiCd and NiMh batteries Here is the circuit diagram of a low cost universal charger for NiCD NiMH batteries. This....
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This circuit arose from the need of the author to provide a 5 V output from the 24 V battery of a solar powered generator. Although solar power is essenti....
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The signal from a microphone is two weak for a standard line input. This low-noise DC-coupled microphone amplifier provides a solution for anyone who want....
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Looking for an efficient USB charger that can operate from a 12V car battery? This unit functions at up to 89% efficiency and can charge USB devices at cu....
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All miniature electronic devices operate off batteries. Some of them need higher than the standard battery voltages to operate efficiently. If the battery....
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Here`s a simple low supply rail detection circuit that costs peanuts and takes just 20 minutes or so to make. Its power consumption is quite low, so it could easily be built into battery-powered devices. Instead of using an op amp, the circuit is built....
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This circuit was designed to produce an audible alarm when the mains power is interrupted. Such an alarm is essential for anyone whose livelihood depends....
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Here is a simple frequency counter designed to monitor the 240VAC mains supply. It as a frequency range of 0-999Hz, so it could also be used with 400Hz eq....
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Small in size! Big in use Here is a simple and powerful LED circuit that can be operated directly from the AC 100 volt to AC 230 Volts mains supply. The c....
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Did it ever occur to you that an array of white LEDs can be used as a small lamp for the living room? If not, read on. LED lamps are available ready-made,....
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Whenever AC mains supply fails, this circuit alerts you by sounding an alarm. It also provides a backup light to help you find your way to the torch or th....
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The detector is intended to sense and signal to another circuit that an appliance is connected to the mains voltage. For this purpose, an optocoupler, IC1....
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The circuit senses mains current supplied to a master` device and switches slave` equipment on or off. This feature is useful in a typical hi-fi or home computer environment where several peripheral devices can all be switched on or off together. A....
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This circuit indicates which of three voltages in the range from about about -4V to about +4V at A, B and C is the highest by lighting one of three in....
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The range of this FM transmitter is around 100 meters at 9V DC supply. The circuit comprises three stages. The first stage is a microphone preamplifier bu....
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In contrast to an ordinary voltmeter, the input of an oscilloscope generally has one side (GND) connected to ground via the mains lead. In certain situati....
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Most thefts happen after midnight hours when people enter the second phase of sleep called ‘paradoxical sleep. Here is an energy-saving circuit that caus....
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A small audio test generator is very useful for quickly tracing a signal through an audio unit. Its main purpose is speed rather than refinement. A single....
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Here s a project that could be useful this summer on the beach, to stop anyone touching your things left on your beach towel while you ve gone swimming; y....
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his handy, pocket-size mobile transmission detector can sense the presence of an activated mobile phone from a distance of one-and-a-half metres. So it ca....
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Stops charging when battery is full charged, Portable unit Charging of the mobile phone, cellphone battery is a big problem while traveling as power suppl....
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Charge your iPod without connecting it to a computer! Using the USB port on your computer to charge your player s batteries is not always practical. What....
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Small and portable unit, Can be assembled on veroboard Mobile phone chargers available in the market are quite expensive. The circuit presented here comes....
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This circuit is the basis for the dimmers in a model theatre lighting system which uses touch globes as the light source. The circuit is based around a 55....
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The modem off indicator is intended especially for serious Internet surfers. It will be seen that the circuit of the indicator cannot be much simpler, or....
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Four high level inputs, Double Bar switching This module can be a necessary addition to the Modular Preamplifier Control Center when more than two sources....
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The light barrier described here can be used to guard an entrance. You can use it to signal of someone is walking through the corridor, or to check if the car has been parked far enough in the garage to be able to close the door. The circuit consists of a....
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High Quality, Discrete Components Design, Input and Tone Control Modules To complement the 60 Watt MosFet Audio Amplifier a High Quality Preamplifier desi....
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This circuit allows an SPST momentary pushbutton to act as a push-on push-off switch, using a DPDT latching (bi-stable) relay. It was originally intended to allow a single pushbutton switch on the dash of a vintage car to provide a latched function. The....
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This circuit automatically turns a motor cycle`s headlight on and off, independently of both the light and ignition switches, provided the battery is fully charged. The first stage uses the 22O resistor and ZD1 to hold transistor Q1 off while the motor is....
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Most PC enclosures provide only a single LED to indicate hard disk access, with the LED being connected to the motherboard via a two-pin connector. However, this LED only works with IDE drives, and if a SCSI disk controller is fitted, its activity will not....
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The continuity tester is a handy adjunct to an ohmmeter. The unit or component whose continuity is to be checked is connected between terminals E1 and E2....
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This circuit charges two NiCad cells with a constant current and features dual charging rates, voltage cutoff and an audible alarm. The circuit is powered....
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The circuit presented here is intended for charging NiMH batteries. The MAX712 IC used here contains all the necessary functionality to make sure that this happens in a controlled manner. Figure 1 shows the schematic of the charger. The heart of the circuit....
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Although this design is reproduced directly from the manufacturer s datasheets, its use in this application is rather novel. Originally intended for high-....
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In this simple circuit we give the chip a little more attention than usual. It is astonishing what can be built with a 555. We are always infatuated with....
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Most homes today have at least a few infrared remote controls, whether they be for the television, the video recorder, the stereo, etc. Despite that fact,....
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This accurate one-pulse-per-second clock is made with a few common parts and driven from a 50 or 60 Hertz mains supply but with no direct connection to it. A beep or metronome-like click and/or a visible flash, will beat the one-second time and can be useful....
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At the heart of this circuit is a precision integrated temperature sensor type LM35 (IC1), which provides an accurately linear and directly proportional o....
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This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm. , D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when....
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There are two types of preamplifiers for magnetic phono cartridges. An example of the most common type is the one described in the March 2002 issue of SIL....
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The fan runs constantly in many PCs, which may not even be necessary. A simple controller circuit can regulate the fan speed according to demand. This not....
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The PC processor generates very high temperature during its operation which is dissipated by the large heat sink placed above the processor. If the heat s....
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This little circuit will help you to remove all surplus small ac mains adaptors from your desktop. The circuit is nothing, but a smart dc power box direct....
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Here s how to build a pendulum-controlled clock which can be made really accurate. Retro? yes, but an interesting project all the same. You ll need a sp....
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Magnetic (or electromagnetic) water descaler devices have been showing up on the shelves of Home Improvement and other DIY stores all over Europe. Despite the numerous studies completed on that subject, by manufacturers as well as by various consumer....
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A flashing LED signals the necessity to water a plant, 3V powered circuit This circuit is intended to signal when a plant needs water. A LED flashes at a....
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There are systems in which it is imperative that the supply voltage of, say, a motor, always has the correct polarity. It is, of course, possible to use a....
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An AC triggered Multitone, polyphonic doorbell. It gives eight melodious tunes for 2 minutes. On each press it will give a new tone which will continue till the melody is over. The circuit is too simple and battery operated It uses the popular melody....
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This circuit is mainly intended to provide common home stereo amplifiers with a microphone input. The battery supply is a good compromise: in this manner the input circuit is free from mains low frequency hum pick-up and connection to the amplifier is more....
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This portable solar lantern circuit uses 6 volt/5 watt solar panels are now widely available. With the help of such a photo-voltaic panel we can construct....
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Modern electronics is indispensable for every large model railroad system, and it provides a solution to almost every problem. Although ready-made product....
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The losses in a bridge rectifier can easily become significant when low voltages are being rectified. The voltage drop across the bridge is a good 1.5 V,....
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More and more equipment is sold that runs off internal rechargeable batteries. Although a matching charger is usually supplied in the package, there are a....
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Simple circuit No ICs required, 12V Battery operation This circuit was requested by several correspondents. Its purpose was to obtain more power than th....
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While we have published a number of variations on a standard RIAA preamplifier for magnetic phono cartridges, we have not published a preamp stage for cer....
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General purpose circuit of the simple pressure sensor alarm is built around a couple of readily available cheap components. Working of this circuit is str....
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A long time ago when telephones were so simple almost nothing could go amiss from an electrical point of view, Telecom operators installed surge protection on all telephone lines exposed to storm risks. Paradoxically, now that we are hooking up delicate and....
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The pulse width of the compact pulse cum frequency modulator can be varied by altering the change-over point of comparator IC1 with a control voltage via....
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This simple circuit enables you to listen to your heartbeat, for instance, while you are exercising. The transducer used for detecting the pulse is an ele....
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400mW RMS into 32 Ohm load, Single-rail Supply Optional Tilt Control This design is derived from the Portable Headphone Amplifier featuring an NPN/PNP c....
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This circuit was designed for use in a hifi showroom, where a choice of speakers could be connected to a stereo amplifier for comparative purposes. It cou....
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If you ever thought of experimenting with pulse-width modulation, this circuit should get you started nicely. We ve kept simplicity in mind and used a dua....
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Acoustic check of transistor and diode junctions, Also suitable as continuity tester Short circuits or broken pcb tracks can be easily recognized by means....
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A radio controlled electronic flash is a useful item in any photographer s kit. Professionals use them all the time. For example, a wedding photographer w....
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It is sometimes necessary for an RC (remote control) model to contain some kind of switching functionality. Some things that come to mind are lights on a....
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According to current legislation in many countries, vintage cars must also be fitted with a fog lamp at the rear. In modern cars, there is a bit of circui....
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This article is of interest only to readers whose bicycle lights are powered by a dynamo. The laws on bicycle lights in the United Kingdom are stricter th....
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Many passive field strength meters have appeared in the past, typically using a 50mA analog meter movement if reasonable sensitivity was to be obtained. T....
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Some relays will become warm if they remain energized for some time. The circuit shown here will actuate the relay as before but then reduce the ‘hold cu....
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A relay circuit to function as a DPDT toggle which is controlled by a momentary switch. I strive to keep my circuits simple with little or no integration (555`s, transistors, etc). The circuit is shown active or on mode. Half of RL1 and RL2 manipulate the....
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This alarm circuit was designed to monitor a mains-powered smoke detector located in a shed (which is used to house dog kennels). It provides complete iso....
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Remote Control Mains Switch As the only electronics engineer in my family and circle of friends, it is sometimes not possible to evade an appeal for help ..
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Using this circuit, you can change the speed of the fan from your couch or bed. Infrared receiver module TSOP1738 is used to receive the infrared signal t....
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An electrically operated rolling shutter usually has a standard control panel with a three-position switch: up, down and stop. If you would like to automa....
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This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret....
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This rotative speed regulator circuit schematic allows to control the holing speed of your borer or driller machine. This project is based on the fact tha....
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Protect your home appliances from voltage spikes with this simple time delay circuit. Whenever power to the appliances is switched on or resumes after mai....