Top Circuits Page 210
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Relays have been around for a long time and though often now replaced with solid state switches, they have unique properties that make them more robust tha....
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The 555 frequency can be varied via adjusting the voltage at pin 5. However, the range and linearity of frequency adjustment is very limited. This is a way....
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This is simply (4) 1N4148 diodes connected in series with a thermal anticipation resistor (R1) heat shrunk together at the end of a (3) wire signal cable ”it is visible on some of the photos. The use of a thermal anticipation resistor is an old HVAC....
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How many have had legitimate problems with the 555 timer? Let me guessit involved the reset line, did it not? We all know that pin 4 must be set high befo....
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There are solutions to this problem—mechanical (push On/push Off switch), electromagnetic (latching relay) and electronic (CMOS logic), but few (if any) go....
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A magnet is placed on the door and a magnetic reed switch on the door casing so when the door is closed the circuit is disabled. When the door is open, the....
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Single Transistor Amplifier Revisited Part 3, Common Base vs Common Emitter Configuration, Update One nagging question that I have long had is this: How do....
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This is different than the standard 555 oscillator circuit in that the LED is placed in the capacitor reset line (pin 7). By doing so, overall current is reduced and the high peak LED current does not flow out of the battery. Since the forward drop of the....
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An DIY RF decibel (or power) meter is an indispensable instrument in any radio workshop. Unfortunately, accurate, wideband models are fairly expensive, and....
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I hate to suggest the specific application `bicycle` because it may be use to protect many items from theft. This anti-theft alarm project is built around....
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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 than in most other countries and a dynamo is, therefore, a rarity in the UK. For safety`s sake, it is....
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UHF indicator or wavemeter is some kind of device that measures frequencies and determines LC circuit frequecy resonance. This device does not need to radiate. The oscillator is build with T1 and T2 (2 x BF494) and can be adjusted with C1 and Lx. The Lx coil....
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The SPDIF monitor is one of the many applications possible with the digital audio interface receiver Type CS8412 from Crystal. Other applications described in earlier issues of this magazine dealt with the decoding of the S/PDIF (Sony/Philips Digital....
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This simple circuit helps you sniff out RF radiation leaking from your transmitter, improper joints, a broken cable or equipment with poor RF shielding. The tester is designed for the 2-m amateur radio band (144-146 MHz in Europe). The instrument has a....
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Nowadays, it is no longer necessary to use discrete components to build oscillators. Instead, many manufacturers provide ready-made voltage-controlled osci....
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For those of us who don t like to get their hands dirty, this simple soil moisture tester quickly checks the state of their plants and how much attention t....
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This simple and cheap circuit is not just for Christmas! There are just two resistors, a small-signal transistor such as a BC547, one ‘flashing LED and a....
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This 24V to 36V linear battery charger is long overdue. While this is an old circuit technique, it is optimized for charging higher voltage lead-acid batte....
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The transmitter is equiped with LM567, tone decoder circuit. Audio signal ( at least 50mVvv ) is amplified with T1 and then it is used to modulate IC1. Infrared transmitter frequency is adjusted with P2 between 25 and 40KHz...
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To be independent of the local radio stations for testing VHF receivers, you need a frequency-modulated oscillator that covers the range of 89. 5 to 108 MHz ” but building such an oscillator using discrete components is not that easy. Maxim now has available....
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This infrared alarm barrier can be used to detect persons passing through doorways, corridors and small gates. The transmitter emits a beam of infrared light which is invisible to the human eye. The buzzer at the output of the receiver is activated when the....
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Together with a good directional antenna this high performance two-stage antenna amplifier for the VHF FM broadcast band will enable you to capture far removed (DX) stations. Alternatively, it will drastically improve reception of FM signals you`ve come to....
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TDA7294 is a monolithic integrated circuit in Multiwatt15 package, with high output power (up to 100W) intended for use as audio class AB amplifier in Hi-F....
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Connecting two TDA2030 thru cheap power transistors we can create a amplifier wich can deliver a higher power. With the components value from the schematic....
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Some experts` think that SMFs may affect the physical well-being of people. If you believe that these experts are right, the magnetic-field meter described will help you find sources of SMFs and determine their strength. These findings may help you reduce....
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This automatic door light switch circuit turns ON a lamp when a door is opened then turns it OFF when the door is opened again. The working principle of th....
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This is a take off from the previously posted bicycle anti-theft alarm. One commenter indicated a desire to adapt it to a threshold step plate vibration de....
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This photoelectric smoke detector circuit uses one LED and 2 LDRs to detect the smoke and sound an alarm. The LM1801 IC is the best choice for this circuit....
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In this intercom schematic, the 8 ohm speakers is used as microphone and listening speaker. The 10K potentiometer controls volume and the total gain can be....
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Timelord, one of our top member is working on a great project: a complete apartment air conditioning based on airflow. You can check out his idea here http....
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When the sun position is changing so does the illumination level on the LDRs and the input voltage for the window comparator is no longer half of the supply voltage thereby the output of the comparator generates informations for the motor that rotates the....
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Hard water has a high concentration of minerals, and of these calcium salts are the most troublesome. But there is a solution coming in form of a cheap diy....
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With this voltage regulator extension circuit you can increase the output current up to 10 A. T1 power transistor has a resistor in the emitter and thus th....
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The original smoke alarm circuit has some problems and has left some hobbyists and students disappointed. Rather than to attempt to solve its many problems, I have created an update that uses the venerable LM741 op amp. It is simpler, more conventional,....
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With this whistle light switch you can turn on and off the lighting installation. The main part of this circuit is the UM3763 IC, produced by UMC. The piezo-ceramic buzzer is used here as a microphone and when it receives a tone frequency between 1. 2 kHz....
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This inexpensive FM radio receiver antenna booster uses the BF324 TO92 style pnp transistor in a grounded-base configuration. The circuit may be used as a....
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This simple 12 volt halogen lamp soft starter circuit extends the life of the halogen lamps by eliminating the sharp rise in the temperature of the filamen....
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This AC Power Monitor continuously watches the AC power line voltage for both under-voltage and missing cycles. When it detects a total of 5 or 6 consecuti....
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This simple FM wireless microphone 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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Here is a high performance radio receiver antenna amplifier for the entire VHF broadcast and PMR band (100-175 MHz) which can be successfully built without....
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Do not let its extreme simplicity deceive you — this thing is useful! I have made many over the years and have even given some away as gifts. Yes multimete....
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This power supply circuit is designed around the garden variety 12VAC landscape lighting transformer. Transformer availability and selection has long been a problem for the experimenter, and has often driven them to experiment with dangerous off-line....
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Shadow sensors are widely used to detect the movement of a person in a confined area. Many circuits published earlier have a serious drawback that only one....
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Simple, highly sensitive capacitive ON/OFF switch pads change the state of a latch and turn on an LED without requiring actual physical human contact. The pad may be insulated. A range of 12mm is easily obtained and sensitivity is adjustable. Central is the....
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The DIAC is a 28V bidirectional (bilateral) trigger device that is used on virtually all inexpensive phase controls. The trigger voltage is somewhat high for phase control of 115VAC. Years ago, there was a similar low voltage (6 to 8V) trigger device called....
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These novel relay driver circuits have the ability to pick up a relay with a coil voltage rating equal to double Vcc. After pickup, the relay armature is h....
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Here is one simple circuit of a general-purpose white LED security light with Passive Infrared (PIR) Motion sensing mechanism. At the heart of the circuit is a PIR sensor module SB0061. SB0061 is a pyroelectric sensor module which developed for human body....
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This kind of sensor switch is suitable for making touch operated bells, buzzers of small toys which operate for a small time and then switch off automatically. The input impedance of the trigger is very high and the touch sensor switch can be triggered by....
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This is a small size led flasher built with the 555 timer IC that is powered from 2 x 1. 5V batteries. The circuit can be used as a flashing metronome, dark room timer, memo-reminder or other similar applications. In figure 1 the LED will be ON for a short....
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This 220V mains operated solid state flashing lamp circuit uses a 555 timer IC to control the ON and OFF times of a triac which controls power to the load ..
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In 1896, Marconi successfully covered a distance of about 3 km using electromagnetic waves. A little later, he established radio contact across water between Lavernock Point, South Wales and Flat Holm Island. The transmitter consisted of a spark inductor....
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This light activated relay circuit presented here uses the 555 timer IC and a light dependent resistor or LDR to form a light sensitive relay in an intruder alarm system or for switching on a lamp at Sun set and off at Sun rise. Potentiometer R1 value must....
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Many microcontroller designs typically mix multiple interfacing methods. A microcontroller (µC) system can be viewed as a system that reads from inpu....
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A light dimmer is quite unusual in a caravan or on a boat. Here we describe how you can make one. So if you would like to be able to adjust the mood when y....
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Build a temperature controller circuit with the 555 IC together with a thermistor resistor divider. The advantage is that a well regulated power supply is not needed. The dividing network consists of adjustable resistor R3, thermistor R4 and R5. When the....
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White Light Emitting Diodes recently available can be used as a powerful alternative to incandescent lamps in lighting applications. Today`s White LEDs are....
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Circuit of the LED solar lantern lights presented here is built around one 6V/1W Solar Panel (PhotoVoltaic Panel) and a 4V/800mAh Lead-Acid Battery. Here,....
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With the aid of this circuit it is possible to listen, using a portable VHF FM radio, to listen to stations that transmit only your local cable network. Bo....
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Servo refers to an error sensing feedback control which is used to correct the performance of a system. Servo motor is a DC motor equipped with a servo mec....
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Safety is a major concern in a good many motor-driven applications. This is true in industrial applications where motion starts when power is applied and e....
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This is a low voltage microphone preamplifier circuit with a 1. 5V power supply. The reference, with a 500 kHz unity-gain bandwidth, is used as a preamplifier with a gain of 100. Its output is fed through a gain-control potentiometer to the op amp, which is....
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Based on NE555 this circuit turns on and off the IC output by a momentary switch. In other words it works as a mechanical latching relay, but the circuit backs to the start condition when you switch off the power supply. This feature is often required in....
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This FM oscillator can be used for wireless audio, microphone and part-15 applications where stable frequency modulated oscillators is needed. Lt can be va....
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Here is the circuit of an Arduino-based Panic Alarm! The wiring is very simple so that even a novice can construct this interesting circuit without any difficulty. Arduino is a family of microcontrollers (tiny computers) and a software creation environment....
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Based on CD4017 and logic gates this electronic circuit switches on a relay if you press four keys in the correct sequence, and backs to the start conditio....
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It is often required to switch electrical appliances from a distance without being a direct line of sight between the transmitter and receiver. As you may....
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If you ever wondered why your trailer Stop/Turn signal lamps are so dim you are not alone. The answer is simply that the typical Stop & Turn Signal Convert....
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Crime in general is still on the rise, and having a security alarm installed is no longer a perquisite of the wealthy! Here is a simple and compact securit....
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A 30 to 50 cm whip antenna provides reception from 10 MHz to over 220 MHz. T1 BF981, a dual-gate MOSFET, provides low noise, high-input impedance and high....
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Faced with the situation to control the time that the light is turned on, engineer Radu Preda from Romania has started experimenting with different circuits to save money spent on electricity. He has designed 2 energy saving lighting circuits, the first one....
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Part Fill valves are widely used in Rainwater tanks. The valve will open once the water level in the tank has fallen to a low posit....
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In order to start the timining you have 2 possibilities: you either connect the START point to ground GND and in this case the timer starts when you connect it to the voltage supply or you can place a switch to start it...
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The automatic fan controller circuit shown in the schematic has 2 comparators with different triggering points that are independently adjustable. LM135 or....
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This light dimmer is used to dim the intensity of 12V light bulbs using the well-known 555 timer that is configured as an astable multivibrator. The pulses....
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When a vehicle is driven on the highway at night, it is required that light beam should be of high density and should illuminate the road at a distance suf....
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This simple and economical IR model train detector circuit is intended especially for those hobbyists who wish to add a smart sensor to detect trains on their model railway track. As can be seen in the schematic diagram, it comprises of a simple infrared....
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This circuit can detect only electrical wires connected to the mains (live wire). It has an LED for visual signalization and a buzzer for audio. As the electrician places the detector closer to the electrical wire the LED will flash at a higher frequency. As....
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Here is a simple RF bug detector that will help you detect spy bugs and can operate up to 2 GHz. Below are some essential things required for this circuit:....
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There are several ways to convert an AC voltage at a wall receptacle into the DC voltage required by a microcontroller. Traditionally, this has been done w....
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The ADP1649 is a very compact, highly efficient, single white LED flash driver for high resolution camera phones that improves picture and video quality in....
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This solar charge control combines multiple features into a single design: 3A current rating, low dropout voltage (LDO), range of voltage adjustment (accom....
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The FM modulator circuit (frequency modulation) is built with a Motorola MC1648P oscillator. Two varactors, Motorola MV-209 are used to frequency modulate the oscillator. The 5000 © potentiometer is used to bias the varactors for the best linearity. The....
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This 70MHz rf power amplifier circuit uses the SD1143 transistor which provides a gain of about 14dB in this design. It uses the fact that a 175MHz device....
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This quartz crystal oscillator circuit has greater stability than a parallel resonance circuit. It generates frequencies up to 30 MHz or even higher if you use BFR91 for T1, T2 transistors and reduce R1 R2 values. The MOSFET buffer insulate the oscillator....
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This beeper circuit will generate an car-splitting 110dB from 9V. The setup uses a single 74C14 (CD40106B) CMOS hex inverting Schmitt-trigger IC, which must be used with a piezoelectric device with a feedback terminal. The feedback terminal is attached to a....
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A simple stereo tv decoder circuit build with MC1310P. Transistor Q1 is an audio amplifier and U1 is used as a 31. 5KHz subcarrier which is similar to 38KHz FM MPX. Pilot frequency is 15. 734KHz. No, it cannot be used with the to decode the stereo signal.....
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The simplest stereo balance meter circuit schematic available on the internet! When Left and Right signals are equal, no output is present from U1 and pin....
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A 27MHz transmitter circuit schematic with MC2833 and 2 FET transistors MPF6660. Using a Motorola MC2833 one-chip FM transmitter, a few support components....
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The 10 meters 27MHz CW radio amplifier is equiped with VN66AF transistor produced by Siliconix wich has some advantages: its cheap, great dielectric insulation and high gain. Here we use VN66AF as an rf amplifier for 10m band (26 30 MHz ). For linear....
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This circuit regulates a DC power output. It has a very wide application range. It can be used to control the speed of a motor, a pump, a toy train, the brightness of a LED or lamp, etc. Practically, it can be used in any application that uses a regulated DC....
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This featured circuit is a musical doorbell. After the button S1 is pressed, a short melody is played. When the button is pressed many times in rapid succession or pressed longer, a different melody is generated and the melody plays longer. The circuit works....
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This circuit generates a tone that sounds very similar to a siren. The generator part of the circuit is made of the combination of PNP and NPN transistors. Toghether, the two transistors build up a free runing multivibrator. If the C2 capacitor was connected....
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The CA3189 IC integrates a symmetrical limiter, a phase demodulator, an audio amplifier, and a logarithmic detector-amplifier. The logarithmic detector-amplifier is the most interesting part of the IC for the above featured circuit. It can be used to enhance....
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The idea for this crystal tester circuit sprung out of the need of testing a large number of oscillator crystals lying unused in a big hobby box. testing the crystals one by one without the appropriate device would have been very slow and a time consuming....
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A rf field indicator is required to verify power stages and transmitters antennas. With this radio field indicator you can measure radiated energy from ant....
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The simple audio mixer circuit is built on common base principle, where input voltages are transformed in alternative currents wich are summed to form the....
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over 1400 top electronics projects and electronic circuits with photos, datasheets and easy to read schematics plus how it works and how to build it ..
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This audio noise filter circuit is a bandpass filter for audio frequency band. It filters unwanted signals that are lower or higher than the audio frequencies. It has 2 filters: a low pass filter and a high pass filter in a cascade configuration. Both....