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FM Transmitter with 2N2218
Posted on Friday, November 18, 2011   •   Category: FM Transmitters

FM Transmitter with 2N2218

Here's simple FM transmitter circuit using medium power 2N2218 transistor. Micropohone is of electret type that connects to two input terminals and the antenna should be a copper wire from 15 to 40 cm. Below is schematic circuit of the fm transmitter.




AM Radio built around LM555
Posted on Sunday, November 13, 2011   •   Category: AM Radio

AM Radio built around LM555

AM radio built around 555 timer chip. The only active device (silicon, germanium, or otherwise) is the LM555. The tuning is accomplished with an inductor and a capacitor, and the LM555 acts as an AM demodulator and class-D power amplifier to drive the speaker. You may be wondering how all this is accomplished with a 555. Here’s how the circuit works: The AM radio signal is tuned by inductor L, which is 300 turns of wire on a 1/2 inch diameter cardboard tube made out of a paper roll, along with the 100pF variable capacitor. One end of the parallel configuration of L and C connects to an antenna (surprisingly long!) and the other end connects to a ground wire which is tied to the AC outlet ground (old books tell you to ground it to a water pipe). So far this is exactly like an AM crystal radio. The 555 timer is configured as a pulse width modulator in a non-traditional configuration. If I used the standard approach and connected the input to the CV pin, the low impedance of the pin would prevent the circuit from receiving any radio signals. I had to invert the circuit and tie both high impedance analog pins, Threshold and Trigger to the radio signal input. This is the reason why the CMOS version of the 555 timer performs much better than the standard bipolar, which has higher input bias current.




Active FM Antenna Booster
Posted on Friday, November 4, 2011   •   Category: Antennas

Active FM Antenna Booster

This is a simple active antenna booster. This amplifier will pull in all distant FM stations clearly. The circuits is configured as a common-emitter tuned RF preamplifier wired around VHF/UHF transistor Q1. Input coil L1 consists of four turns of 20SWG enameled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration of transistor 2SC2570 is shown in the fm antenna booster schematic. Adjust input/output trimmers (VC1/VC2) for maximum gain.




Low Power Stereo Amplifier with TDA2822
Posted on Friday, November 4, 2011   •   Category: Amplifiers

Low Power Stereo Amplifier with TDA2822

Here's low power stereo amplifier built around TDA2822 chip. Many people may have heard of the TDA2822 before, but for those who haven't, it is a small power amplifier that will drive two channels. It is usually in an 8-pin DIL package, but older versions I have seen are 14-pin or similar (there are datasheets for both variants). For simplicity though, my circuits show schematics for the 8-pin DIL package. The datasheet is here, provided by ST. This article is based along the usage of the TDA2822M variant of the chip series as it is commonly available. The TDA2822 is similar, but has slightly more pins so is less used.




1W Linear FM Transmitter Booster with 2N4427
Posted on Friday, October 28, 2011   •   Category: FM Transmitters

1W Linear FM Transmitter Booster with 2N4427

Here's 1W RF Amplifier is for boosting small fm transmitters and bugs. It use two Philips 2N4427 and its power is about 1Watt. At the output you can drive any linear with BGY133 or BLY87 and so on. Its power supply has to give 500mA current at 12 Volts. More voltage can boost the distance but the transistors will be burned much earlier than usual.! In any case do not exceed the 15Volts. The Amp offers 15 dB in the area of 80Mhz to 110 Mhz. L4, L5, and L6 are 5mm diameter air coils, 8 turns, with wire 1mm wire diameter.An easy project, with great results.




Stereo Audio Amplifier with TDA2616
Posted on Thursday, October 27, 2011   •   Category: Amplifiers

Stereo Audio Amplifier with TDA2616

I built my first power amplifier when I was still in secondary school. The circuit was made of transistors, didn't provide much power and had an ugly PCB. Around the same time I got access to a datasheet of TDA1524, a tone/volume control circuit, and I decided to use it to build a pre-amplifier, to improve the quality of the sound coming out of the amplifer. Both circuits worked well for almost a decade but the old amplifier was never up to my expectations. In 2006 I decided that it was time to build a real power amplifier, this time based on an integrated circuit to reduce the number of external components and cost.




Stereo FM Transmitter with BA1404
Posted on Sunday, October 23, 2011   •   Category: FM Transmitters

Stereo FM Transmitter with BA1404

A high quality stereo FM transmitter circuit is shown here. The circuit is based on the IC BA1404 from ROHM Semiconductors. BA1404 is a monolithic FM stereo modulator that has built in stereo modulator, FM modulator and RF amplifier. The FM modulator can be operated from 76 to 108MHz and power supply for the circuit can be anything between 1.25 to 3 volts. In the circuit R7, C16, C14 and R6, C15, C13 forms the pre-emphasis network for the right and left channels respectively. This is done for matching the frequency response of the FM transmitter with the FM receiver. Inductor L1 and capacitor C5 is used to set the oscillator frequency. Network C9,C10, R4,R5 improves the channel separation. 38kHz crystal X1 is connected between pins 5 and 6 of the IC. Composite stereo signal is created by the stereo modulator circuit using the 38kHz quartz controlled frequency.




LM317 Overvoltage Protection
Posted on Sunday, October 23, 2011   •   Category: Power Supplies

LM317 Overvoltage Protection

This is an add-on over voltage protection circuit for LM317 voltage regulator. It is a voltage regulator that allows a 6V portable supply to be derived from the 12V car battery. You can add a 6.2V zener diode and a LED to warn you when the input supply is overvoltage. If you could find a relay that would operate from 6.2V right up to 12v that you could connect in such a way that if over voltage occurred, then the relay would automatically switch off the output preventing damage to any connected equipment. Such a relay would be quite difficult to find, so I designed this, it is a simple two transistor circuit which will switch off the output should the voltage raise above 6.2v this can be changed by selecting a different value of zener diode.




Simplest FM Transmitter
Posted on Tuesday, October 18, 2011   •   Category: FM Transmitters

Simplest FM Transmitter

This simple FM Transmitter takes audio input through a 1/4" phono jack and, constructed as shown, without the optional antenna connections, will broadcast an FM radio signal about 30 feet. This is the standard model of simplest FM transmitters includes a trim capacitor to adjust the transmitting frequency. It can be powered by a 9V battery and uses a hand-turned copper coil. The circuit is extraordinarily simple and could be built on perfboard or on a panel almost as easily.




Simple FM Transmitter Bug
Posted on Wednesday, October 12, 2011   •   Category: FM Transmitters

Simple FM Transmitter Bug

This is a simple design of a small FM Transmitter Bug that's perfect for transmitting and eavesdropping purposes. Due to the high sensitivity, even the ticking of the clock to hear. The range is estimated at anything from 50 meters. With a small piece of wire as an antenna to get at least the whole house. L1 and L2 are two equal air pools. They each consist of 5 turns at a diameter of about 4 mm. The thickness of the wire does not matter, 0.5 mm works perfectly. C4 is the frequency adjustment. Tune an FM radio in an empty area of the FM band and C4 to turn your silence or hear a whistle. From what you can precisely adjust the radio and the transmitter installed in a room somewhere to intercept. Note: Because these transmitter bugs inherently unstable, you better read the short legs of the components keep the circuit mechanically tightly together up. Also placing a 1 nF capacitor (C6) will benefit stability. R1, R3, R4: 4K7 R2: 100K R5: 10K R6: 270 Ohms C1, C2: 10 uF C3, C6: 1 nF C4: 2-18 pF trimmer C5: 5.6 pF L1, L2: air puddle windings on May 4 mm in diameter (see text) T1, T2: 547 BC Condenser microphone Original Text: Ook het plaatsen van een 1 nF condensatortje (C6) over de voedingsaanluitingen komt de werking ten goede. [Origineel TinyCAD ontwerp] Show alternative translations




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