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Cordless FM MIC
The Cordless FM Mic can be used as an FM transmitter. The frequency transmitted by the circuit is FM modulated and hence the voice at condenser microphone can be listened to through a standard FM receiver.
Things which you can learn:
*Concepts related to FM modulation and transmission.
*Application of NPN transistors as signal amplifiers.
*Application of the condenser mic as an input device.
Build a simple circuit which can be used as a one-way walkie talkie. Use this kit to transmit your voice over FM and receive the sound in a standard FM receiver.
The circuit of the Cordless FM Mic consists of a high-frequency air core coil (L1) with six closely wound turns of 25 SWG enameled copper wire on 4 mm diameter air former. The range of this transmitter can be enhanced by connecting a 30-60cm long wire as an antenna and changing the value of the 0.0015 micro Farad capacitor to up to 33 Pico Farad.
The range and transmitted frequency can be changed by increasing or decreasing the length of wire which is connected to a collector of NPN transistor 2N2369 (T2)via a capacitor. NPN transistor BC548 (T1) works as a condenser mic amplifier and T2 works as an FM oscillator and modulator by the help of other passive components. The main advantage of this transmitter is that it works off a 3V battery which can be easily obtained from two AA size pencil batteries.