Easy and low cost FM transmitter DIY kit

I recently made a simple DIY FM transmitter kit for amateurs and electronics beginners. With this DIY kit, you can transmit your voice or audio over an ordinary FM radio within the FM broadcast band.

You can use this FM transmitter in two ways:

a. Audio transmission using electret microphone: You can transmit your voice to FM radio with the electret microphone. You can also place the transmitter circuit close to any loud speaker so that the microphone picks up the sound and transmits to the tuned FM radio.

b. Audio transmission connecting speaker stereo jack to audio source:For hearing better sound, you may connect it to your computer, ipod or mp3 player using a speaker jack. The audio of your music players get transmitted to your nearby radio.

Features:

Frequency Range: 88-108MHZ (Frequency can be changed by moving the inductor coil).

Operating voltage: 1. 5V-9V

Transmission range: More than 30 meters in open area. The transmission depends upon the length of antenna used. I used just a simple 10cm long wire. The signal can be transmitted even far with longer antenna of length around 50cm.

Testing of the kit:

Find an FM radio, turn on the power and volume, adjust the frequency around 88 MHz. Connect the kit to the power supply board, align towards the radio and use a screwdriver to adjust the oscillation coil L until the radio catches the signal. Then slowly increase the distance between the microphone and radio, while properly adjusting the radio (or handset) volume, tuning knob until the clearest sound is heard.


Source -: Instructables