Tuesday, December 31, 2013

FM Radio Station Microphonic Part 25

FM RADIO STATION MICROPHONIC PART 25

HOW DO YOU TRANSMIT VOICE WITHOUT A MICROPHONE?

This is a two transistor circuit that makes up a wireless FM radio transmitter with a remarkable feature - it transmits voice without a microphone! 

It uses a floppy coil that moves upon receiving the vibrations from speech or other sources.


"This means it will vibrate when bumped and will even pick up sounds such as talking, music and footsteps and transmit audio just like a microphone.

Forget the phone lines as they are not needed for this example. Build the circuit and use 7 turns of thin wire on an 8-10mm pen and see how the coil picks up every sound in the room. Simply connect a 9v supply and the circuit starts broadcasting. The coil should be 6t and 3mm diameter, using 0.5mm enamelled wire."

Source
http://www.talkingelectronics.com/projects/Spy%20Circuits/SpyCircuits-3.html