FM adaptor circuit for car stereo

jacky April 7, 2010 7 Comments


With this compact FM adaptor circuit plugged into the audio out of your cassete player or i Pod out put,you can listen your favorite music on your car stereo.This circuit is very useful if your car stereo doesnot have an auxillary in socket.The circuit is nothing buy  an short range  FM transimitter.

The FM transmitter circuit is based on low power NPN transistor 2N2222.The tank circuit consisting of L1 & C1 producess the necessary oscillations at the collector of Q1.The capacitance C4 , resistance R3 & R4  performs the function of mixing the stereo out put from theaudio player or i-Pod.The emitter resistance R2 provides sufficient stability to the circuit.It also limits the collector current to increse the battery life.

Circuit diagram with Parts list.



  • Use a 28SWG , 10 cm insulated copper wire as antenna.
  • For L1.make 8 turns of 20 SWG insulated copper wire on a 5mm dia plastic former.
  • Power the circuit from a 3V battery.
  • Assemble the circuit on a good quality PCB or common board.
  • C1 can be a  50pF trimmer.
  • amit
    July 1, 2014

    Is all these capacitor use in this are ceramic ?

    • seetharaman
      July 2, 2014

      Yes all are ceramic capacitors. Variable capacitor is mica dielectric preset capacitor.

  • gregtherider
    January 28, 2011

    Is this working on FM or AM modulation? I suppose AM.
    What s the frequency? Built it but can find it on the radio..

  • peter nyondo
    March 4, 2009

    This a very good idea but at what frequency. i tried it but it overrides the National radio(MBC1). thanks

    peter from malawi

  • ghost303
    February 4, 2009

    really nice idea

    Im thinking of adapting this into a wireless stereo transmitter for my computer and a receiver for some headphones

    Voila – Wireless Headset for under $40

  • Vikesh
    January 22, 2009

    hi i realy like this idea. but i wonder what frequency the transmitter is broadcasting on, and how can i regulate the frequency so i dont interfere with other radio stations nearby. thanks

  • Ahmed elshaer
    January 18, 2009

    Thanks for this circuit, but i want to know how to control the carrier frequency in order not to interfere with any radio station?
    Thank you in advance.

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