Rongge

Description. This could be the simplest FM transmitter circuit you can find on the internet. Only using a single transistor and few passive components, this transmitter can deliver signals up to 50 meters. The transistor Q1 serves as the modulator as well as oscillator. Capacitor C2 and inductor L1 forms the necessary tank circuit for making oscillation. The voice to be transmitted is coupled to the base of Q1 using an electret microphone. The FM signal available at the collector of Q1 is radiated using the antenna. Circuit diagram. Notes. Use a 3V battery for powering the circuit. The circuit can be assembled on a Vero board. Coil L1 can be made by making 5 turns of 24AWG wire on a 1cm plastic former. Adjustments in the transmission frequency can be made by compressing or relaxing the coil. Antenna can be a 25cm long 18AWG wire.

Miniature FM Transmitter Circuit Diagram  Notes : The default for the capacitors type is ceramic, preferably the npo 1% (low noise) type or equivalent. But basically nothing critical here. Use any capacitor you have laying around, but NO electrolytic or tantalum caps. Only if you intend to use this circuit outside the home you may want to select more temperature stable capacitors. To find the signal on your receiver, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver.