Top Circuits Page 207
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In this fire alarm circuit project, a thermistor works as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal....
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It relies on the smoke that is produced in the event of a fire and passes between a bulb and an LDR, the amount of light falling on the LDR decreases. This type of circuit is called optical smoke detector. Do not use it as a home smoke detector it`s jus for....
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This simple and cost-effective ding dong electronic doorbell circuit is based on IC 8021-2. The IC has an in-built circuitry to produce ding dong sound each time its pin 3 is pulled low. The sound is stored in the IC as bits, as in a ROM. The sound output....
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There are many ultrasonic pest repellent devices available on the market but a major drawback is that their power output is low and their effectiveness suf....
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This miniature audio amplifier delivers up to 250mW and can be used like a final stage audio amplifier for radio sets. The schematic is very simple: one BC....
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This is very stable, harmonic free, long range fm transmitter circuit which can be used for fm frequencies between 88 and 108 MHz. This can cover 5km range....
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This is a regulated and adjustable power supply which can deliver up to 20A and adjustable voltage between 4 and 30V. It is easy to build and uses LM338 an....
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This circuit generate sine wave oscillation, but actually we can modify the circuit to generate triangle or square wave function. The frequency can be controlled using current. If we disconnect the 20k RIN from REF (pin 1) and connect it to a DAC, then we....
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VOX is a voice controlled switch, used often for microphones replacing the classic switching button. The actuating threshold is set thru the volume potenti....
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This circuit project automatically turns on a night lamp when bedroom light is switched off. The lamp remains ON until the light sensor senses daylight in....
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The microphone preamplifier circuit design presented in this schematic use SSM2015 produced by Precision Monolithics Inc. (PMI) which offers a high amplification and low noise ( 1. 3nV/ f). Has been designed to work with differential input signals and can....
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This sound wattmeter uses a row of colored LEDs as a scale to show the relative power output of your amplifier in watts. It is easy to be inserted into the speaker box. All you need is to hook a supply voltage to it. The value of R1 depends upon the....
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This sound controlled lights circuit design is used to control the brightness of the lights attached to it in sync with the sound that is being capturated....
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The first reverberator we present is based on TDA1022, the most used BBD. Reverberator adjustements for proper functionality Before we connect the power su....
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This single transistor audio mixer is used in an amplifier circuit design with base driven transistor and with its emitter being current controlled, most o....
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This infrared detector circuit uses a passive IR-detector component PID20. It converts heat radiation into electrical impulses. The output voltage of the PID20 increases when an object comes close to it, this object must be warmer than the surroundings. The....
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The digital sine wave generator (oscillator) circuit has the advantage that only few components are needed to generate signals with high amplitude constants and variable within a very wide range of frequencies. The circuit shown here generates a sinewave....
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Filters with high orders are designed usually with 2 or more cascaded sections. This order 4 filter need only one OA IC , so we can achieve lower distorsio....
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This class A preamplifier has been designed in a symmetrical structure. In the input differential stages we`ve used the dual transistors T1 and T2. Polarisation correction is essential because of the amplification differences and is assured with T12. P2....
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This PIN diode rf switch is the ideal antenna switch for VHF and UHF and work with the PIN diodes which are special high frequency switching diodes with ve....
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This car stereo booster uses an LM2896 IC which has two integrated amplifiers. It can be powered with voltages up to 15 volts. The power output is 2. 5 watts per channel with an 8 © load and supply voltage of 12 volts. Using the bridge tehnique in the....
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A simple USB FM transmitter that could be used to play audio files from an MP3 player or computer on a standard VHF FM radio by connecting it to an USB port. The circuit use no coils that have to be wound. This USB transmitter can be used to listen to your....
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This small video transmitter is very usefull for video surveillance on short distances ( up to 100m ) equipped with a black and white or infrared camera module it delivers excellent pictures on a standard color or b/w tv. Instead of BFY90 you can use any VHF....
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This simple stereo encoder circuit schematic is build with 2 IC MMC4066E and MMC4047 and one transistor BC547B. On IC1 2 and 3 pins is the audio output whi....
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A very simple DIY crystal oscillator circuit which use a quartz for frequency stability and a good rf transistor. Use a 2-nd or 3-rd harmonic crystal, for....
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In this halogen switch circuit we use a FET transistor because the current is dependent of the FET`s gate voltage. The maximum gate voltage is 12V, so this circuit is adequate for 12 volt lamps. R1 value is 100 k © for 6V and 470 k © for 12V. You can use....
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A very simple audio compressor built with SSM2165 IC. There is no much explication about this compressor circuit schematic, just pay attention at capacitor....
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The simplest one transistor audio mixer circuit diagram on the net. It has only one transistor and can support as many audio signal as you can afford. BC10....
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A very simple and cheap tv antenna amplifier circuit built with BF961 a NChannel Dual Gate MOS common transistor used for input and mixer stages especiall....
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This fm rf power amplifier circuit is built with BLY94 transistor which delivers up to 50W at 175MHz and has a power gain of 7dB, arround 5x power amplification. But in this schematic bly94 is working in 3 meter band, FM 88-108 MHz, so it has a higher power....
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This is a diy simple stun gun circuit showned only for learning! In No Way Do I Recommend Building these Stun-Guns or the actual use of them for any purpos....
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A basic UUS 65 73 MHz fm transmitter circuit schematic which can be used as UUS oscillator with no explanation 65 - 73 MHz transmitter ( oscillator ) c....
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A very usefull talk over circuit which you can use in your radio stations, club or anywhere you want to speak over music without any movement of potentiome....
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Circuit consists of an oscillator with variable frequency, a divided frequency and measurement stage. The Oscillator is based on a inversor from a 74HC14 and generates a frequency f inversely proportional to the Cx placed between terminals. During a half....
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This PWM Controller circuit is ideal for controlling small motors with 2A maximum current consumption. For higher currents you need additional cooling for....
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This subwoofer active filter circuit is a 24 dB octave filter with a Bessel character and cutoff frequency of 200 Hz. So, if you are interested in experimenting with audio circuits in subwoofer range, this circuit is for you. In subwoofer range, all audio....
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The total gain of the car antenna amplifier is around 30 dB and the input impedance at 30 Mhz is around 10 K ©. The amplifier must be mounted directly at the base of the antenna to avoid signal losses caused by the capacitive character of the coaxial cable.....
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This sawtooth generator circuit use 741 IC and is used as a musical sound synthesizer. The sawtooth input signal is continously changed through P2 to a wav....
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SWR or standing wave ratio is the ratio of the amplitude of a partial standing wave at an antinode (maximum) to the amplitude at an adjacent node (minimum)....
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VOX is a switch ordered by voice, often used at microphones instead of the classic switch button. The vox described here may be connected to almost any type of audio equipment which has an external speaker for coupling. The threshold action is set with....
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This Ultrasonic Sensor Circuit consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered the circuit`s fine balance is disturbed and the alarm is triggered. The ultrasonic circuit....
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The final amplifier is the power source of every audio installation. Its job is to convert a small alternating voltage into a powerful signal for driving l....
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This 900 MHz Amplifier Circuit is built with BFG480W which has a good linearity performance. Therefore the BFG480W is well suited for LNAs with high linear....
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The portable batteries charger has been designed to provide an opportunity to load NiCd batteries even in the outdoors from a 12 V battery of a vehicle. Wh....
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This is the simple version of a white LED lamp that can be directly powered from mains. It can give ample light even for reading purpose. Capacitor Cx alon....
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Here is an ultra sensitive earthquake detector circuit that can sense seismic vibrations. It can be used to detect vibrations in the Earth. So it is an ide....
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The transmitter on 2 meters 144 MHz was designed mainly for use by radio amateurs as radio beacon and to this end, it produces a signal of good quality and....
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Here are 2 heat sensor circuits, first one is build with the 4060 IC, the second one is simpler than the one before and has fewer components. It is an idea....
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This simple circuit senses heat from electronic devices and gives warning alarm. It is an ideal add on circuit to monitor heat in CD players, Amplifiers etc. The circuit uses 14 stage ripple free binary counter IC CD 4060. It has an internal oscillator and....
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This circuit delivers an initial voltage of 2.5V per cell to rapidly charge a car battery. The charging current decreases as the battery charges and when t....
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This is a Preselector for SW receivers (diy hf preselector) circuit. The entry low capacitance of MOSFET modern, with two gates, will create negative inverse reaction through a uncoupled source resistor. Applied right this technique allows the creation of a....
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Modern acid batteries and lead plates, are embodiment of simplicity in use. Unlike NiCd batteries, they must be recharged by connecting to a constant volta....
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CGA to SCART adapter has great advantages as it does not require separate power source and that uses very few external components, which can be easily adapted in the SCART connector. The signals from R, G and B pins of the CGA`s board are converted from TTL....
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Protect your Locker or Briefcase from theft using this pocket sized gadget. It gives a loud police siren to catch attention. The circuit uses a single IC a....
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The brightness of a fluorescent light bulb or neon tube cannot adjust as easily as that of a incandescent bulb because it starts only when a voltage is much higher than that of the network, then remains on at electrical network voltage. Normally, the high....
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This Infrared transmitter can activate IR based switching circuits from a distance of 10 meters or more. It is a high power IR transmitter driving two IR L....
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Here is the circuit of an ultra sensitive IR receiver that can be used to switch on various AC devices through an IR transmitter. It uses the Photo transis....
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SFH505A made by Siemens combine infrared diode receiver, amplifier, demodulator and a filter band pass for minimizing interferences. This circuit works tog....
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The main component of this 3 band graphic equalizer is LM833 produced by National Semiconductor. LM833 has a very low noise, and a band / amplifier of 15MH....
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This infrared tranmitter is intended for use with this infrared receiver. It works with 2 - 1.5V batteries or a 3V lithium battery. To give a compact infra....
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This FET audio mixer is an example of FET`s versatility. FETs are originally designed for high frequency applications but they can be used for audio frequencies and in fact they perform excellently in this area. The number of inputs that can be connected to....
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This simple power mosfet audio amplifier circuit, with TL071C and 2 MOSFETs (IRF9530 and IRF530) can deliver up to 45 Watts on 8 © speaker. This schematic is based on Siliconix application and on variations of voltage on the 2 resistors that are serial....
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Here is an ideal mobile charger using 1.5 volt pen cells to charge mobile phone while traveling. It can replenish cell phone battery three or four times in....
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This cable tv amplifier circuit is a rf amplifier designed to be quickly installed between two coaxial cables. Both input and output impedances are compatible with 75 © cables. The main amplifier si T1 transistor, T2 is working as an emitter follower. The....
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Modern power control systems utilize electronic devices like Thyristors for power switching, phase control, chopper etc. These devices also find applicatio....
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A sensitive and reliable rf field strength meter is an invaluable instrument in amateur radio and in radio controlled model area. A field strength meter is used to align an antenna to get the best possible gain, to determine the transmitting range of radio....
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This motor speed controller uses a single IC LM1014 to control the speed of a DC motor. It senses the increase in the motor-current when the rotation of th....
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This digital thermometer circuit diagram uses a common 1N4148 diode as the temperature sensor. The temperature coefficient of the diode, -2 mV/°C is ex....
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This FM spy telephone circuit is mounted serrial with the phone line. When is signal on the wires this transmitter will radiate airwaves thru the wires wic....
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The most important part of this 88-108 transmitter is the Colpitts oscillator. C3,C4,C5,C6,CD1-CD2 ans L1 determine the transmission frequency. The RF Osci....
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This fire sensor circuit exploits the temperature sensing property of an ordinary signal diode IN 34 to detect heat from fire. At the moment it senses heat, a loud alarm simulating that of Fire brigade will be produced. The circuit is too sensitive and can....
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This triac-based 220V AC motor speed controller circuit is designed for controlling the speed of small household motors like drill machines. The speed of the motor can be controlled by changing the setting of P1. The setting of P1 determines the phase of the....
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Here is a simple logic state indicator to test whether the output of digital IC is in logic 1 or 0. The Bicolor LED lights Green when the logic state is 1....
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This amplifier circuit is used to amplify TV signals in UHF range. It uses a low-noise transistor and gives 10 to 15 dB amplification in the frequency range from 400 MHz to 850 MHz. The transistor must be shielded from the input components and in....
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This is probably the simplest idea to generate flashing light from an LED using AC. The circuit is relatively the simple way of flashing one or more LEDs from a high voltage DC obtained from Mains. This can be used as a Mains indicator or Mock flasher. The....
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This digital DIY tachometer for bikes uses two reed switches to get the speed information of the bicycle. The reed switches are installed near the rim of the wheel where permanent magnets pass by. The permanent magnets are attached to the wheelspokes and....
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This simple water level sensor circuit monitors the presence of water in a certain location or container. The circuit sends an acoustic alarm when it sense....
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This is a small tv transmitter circuit wich trasmittes in VHF, negative sound modulation and PAL video modulation. It is suitable in countries where the B and G system is used. T1 which type of transformer. what is C1 value. what means of letter P which in....
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THis Wien bridge oscillator is very simple and as every wien oscillator has low distorsion and the resonance frequency can be easily adjusted. This frequen....
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This mosfet fm transmitter circuit is designed to be used for aligning FM radio receivers. It has a microphone amplifier with automatic gain control. The FM modulation is a voltage oscillator and the final stage is built with MOSFETs. A lowpass filter at the....
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Sometimes I can find a station and sometimes I can`t find any stations. Probably the main problem when tuning is, as soon as you move your hands or body, let go of the tuning cap or touch the 10k pot, whatever station you had on will either disappear or....
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This fatigue testing circuit is very simple and easy to build and will determine how tired a person is. It has been discovered that the highest light frequ....
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This 2 meter 144 MHz fox hunt transmitter is used in amateur competitions where a hidden transmitter is to be ""hunted"" using mostly homebrewed receivers an....
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Here is a solar charger circuit that is used to charge Lead Acid or Ni-Cd batteries using the solar energy power. The circuit harvests solar energy to char....
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This add on circuit can be attached to the solar charger to see whether the battery is charging or not. It lights a Red LED to indicate that the battery is....
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The function of this automatic volume control circuit is to amplify signals without distorting its dynamic compression. The amplitude differences in the signal are levelled off and the disturbing effect vanish. With this tehnique, overcompensation in the....
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This voltage to frequency converter circuit has an oscillator that is voltage controlled and has a small, 0. 5% deviation. IC1 function as a multivibrator and produces rectangular impulses with equal width. The output frequency can be easily adjusted with....
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This white LED flood lights illuminates your porch with cool white light. The circuit is too simple and energy saving design. Its current consumption is pr....
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At low output power, up to 18 W, the device operates as a normal BTL amplifier. When a larger output voltage swing is required, the internal supply voltage is lifted by means of the external electrolytic capacitors. Due to this momentarily higher supply....
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An ideal solution to harvest Solar energy for charging purpose. This charger can replenish almost all types of batteries including Mobile phone battery. It uses a Solar Module to convert light energy into electrical energy The circuit is self explanatory. A....
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UM3561 is an excellent ROM IC that can generate Multi siren tones simulating Police siren, Ambulance siren, Fire brigade siren and Machine gun sound. This 8 pin low power IC can work down to 2. 4 volts. The UM 3561 is a low cost siren generator designed for....
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Protect your equipments with this tiny 12V time delay relay circuit. The SMPS based power supply of these modern electronic devices is vulnerable to spikes....
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Here is a simple Battery Monitor circuit for a quick check of 12 volt Lead-Acid Battery. Battery charge should be constantly monitored to increase the life....
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Pachisi game is designed for two persons. Each player has one figurine; the figurines are found in the early game on positions indicated by arrows. The goa....
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A 1Hz pulse/frequency generator using the popular timer IC 555 which is wired as an Astable Multivibrator. The output pulses can be indicated visually by the LED. An Astable Multivibrator, often called a free-running Multivibrator, is a rectangular-wave....
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This simple Mock Flasher LED simulates the indicator of a sophisticated Alarm system. It can be placed in doors, gates and vehicles to confuse intruders. T....
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With this technique, an extra cable to power the fm antenna amplifier is unnecessary. The RF signal and the DC current supplying the amplifier use the cable simultaneously. Check another FM antenna booster circuit diagram. The RF signal is however prevented....
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This laser door alarm is based on the interruption of Laser beam. A low cost Laser pointer is used as the source of light beam. When somebody breaks the la....
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This PC fan controller circuit is designed with discrete components and is used to control 12 V fans that have a current consumption lower than 200mA. With the components values presented in the circuit diagram, the voltage won`t drop below 7V. If the fan....