FM Transmitter with Wireless Feature

The wireless FM transmitter project enables a user to speak into the transmitter using a microphone where the voice can be heard on any FM radio within 25ft.

To construct the FM transmitter, a combination of wire wrapping and soldering was used. The positive and negative leads of a battery were connected to the two pins of an electrets microphone with the pad connecting to the negative lead physically touching the casing of the microphone’s casing. The batteries used were coin cells but can be replaced with regular 1.5V AA although coin cells take less room. The other components include the 2N2222 transistor, variable capacitor, inductor, and the antenna made of solid strand 22 gauge wires.

During the operation, the variable capacitor and the inductor, making up a parallel LC tank circuit, will vibrate at 88-108MHz frequencies in the FM radio. The capacitor across the transistor serves to keep the tank circuit vibrating while another capacitor maintains a constant voltage. The voice will be modulated to transmit at a frequency between 88 and 108MHz and the voice can be heard if a nearby pocket FM radio is tuned when speaking into the transmitter.