Miniature FM transmitter

john September 21, 2009 59 Comments

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.

miniature FM transmitter

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.

Comments
  • Kuldeep Tripathi
    February 20, 2015

    In your Circuit the signal is catch by mobile FM radio .

  • Niels
    December 5, 2014

    Dear inventor lol,

    If i change the supply voltage to 9V and also change the resistor of 4,7k.
    Wil the circuit deliver more power? and also more meters?

  • November 8, 2014

    sir,i am a beginner however i made this circuit and dont know what to do now….i searched the channel through phone fm and found nothing…plz help.

  • Rasel
    August 20, 2014

    Sir,Do it woak by mobile fm reciver?

  • Arielle Mae Ilagan
    July 11, 2014

    Just use the resonant frequency formula? Would that be okay? No other changes in the value of other components?

  • Arielle Mae Ilagan
    July 11, 2014

    Hi, sir. We have FM transmitter as our midterms project. But our professor said that it should transmit at an exact frequency. Say, 89.9. What adjustments should i make?

  • pranav
    April 15, 2014

    Thank u seetharaman
    its working and i choose a variable cap instead of capacitor in the tank ckt..
    Thanks for ur valuable support..

  • pranav
    April 7, 2014

    What is the inductance of the coil
    what is the frequency range…?

    • Seetharaman
      April 7, 2014

      Please wind the coil as per data and use, trying to buy with uH value will not help you in completing the project successfully. It will operate in the range of 88 to 108MHz you can use your standard FM receiver to monitor the signal.

  • Bella David
    March 20, 2014

    i made dis miniature fm transmitter on a Veno board though with slight variation; i used 0.001uf instead of 0.01uf, 22pf instead of 33pf, 0.001uf instead of 6:8pf, and little alterations too wr made to d resistors. I did these bcos i could’nt lay my hands on d exact capacitors and resitors. Well, unfortunately for me it didn’t work. Pls i dnt knw why. Thought i could use some help from ya folks!

  • Rex
    January 22, 2014

    How can i make this transmitter frequency stable

  • Rex
    January 22, 2014

    Seetharaman, apart from shelding the circuit with metal, give me more ideas on how to make the transmitter frequency stable

  • November 14, 2013

    I made a simple radio redio receiver several times but i couldnt succed in receiving stations, but i made transistor amplifiers and it works, so please i would like to know where the problems is/are arrising, thanks

  • Kamaluddeenkmc
    November 13, 2013

    Any problems you get from this miniature fm transmitter is from the transistor, so check your transistor,

  • sanjiv
    November 12, 2013

    want to know how doors are open & closed in big Mall , Hotel when any one go in-front of it??? The principal, sencers & Circuit if you have??? Regards…
    Sanjiv….

  • Walid
    October 26, 2013

    I used 7 pF instead C3 6.8pF. When I do a scan with my phone no new radio discovered. Voltage on microphone is 0.7V (Electret microphone need 1.5V).
    What’s wrong ?
    I need to build this circuit, please help !

  • i think i can replace the transistor to high power type to increase the srength

  • Anjana
    April 15, 2013

    when i connected the circuit it was working at 105.30MHz but now it is not at all working why is this so??????
    i checked all the connections it was all right.

  • Rakesh suthar
    April 13, 2013

    are you sure this fm transmetter circuit work corectay

  • April 4, 2013

    Hi this a good and simple circuit, but instead of using a fix capacitor at C2, done u think a variable capacitor can be used there to vary the frequency instead of using the coil. And a C119 transistor can replace the Q1?

    • Seetharaman
      April 5, 2013

      Hi yes you can use a 4.7PF fixed capacitor with 22PF variable capacitor.
      2N2222 is the best choice. you can try C119.

  • Tushar Gupta
    September 16, 2012

    http://www.aaroncake.net/circuits/fmtrans.asp

    will the above circuit given in the link work..

    also suppose..if i only wnat to use a single band..that is fixed at one frequency..what value of inductance and capacitance should i use..??

    Also any idea on how to simulate this in software..??

  • September 15, 2012

    hello all,
    please i wont to know more about the radio transmitter
    and the value of components example 10uf/16v.
    give us those title if we can build same.
    thank you
    all the best.

  • Himanshu
    September 10, 2012

    Can we replace electret microphone by 3.5mm port so that AUX cable can be used?

  • kiran
    July 14, 2012

    hi sir what is FM transmitter and receiver exactly?and can i use it to transmit music and receive.how to do that?

  • ameh
    March 27, 2012

    where’s the prototype? can we see it?:D

  • ameh
    March 27, 2012

    can i use 7PF for x3 instead of 6.8pF?

  • Jesse
    January 3, 2012

    Thanks for this circuit !
    Most oscillators I tried were not working.

  • Anish
    July 31, 2011

    Thanks for the circuit idea for the poster and your valuable support Mr. Seetharaman, the circuit worked like a charm… but i face two problems…

    1. It works for about 3metres without antenna. But if i insert the antenna, the frequency chages. what to do?
    2. I assembled the circuit yesterday night and left it in a working condition undisturbed. I only disconnected the power. But today morning, the frequency is changed by itself! So, will it change like this?

    PS: I assembled it on a solderless bread board

  • seetharaman
    July 31, 2011

    Hi Anish rigid one. seethe coil wound on orange pvc former
    http://www.vk2zay.net/article/173

  • Anish
    July 31, 2011

    Thanks for your reply sir,
    the plastic conduit.. the flexible one or rigid one? Can you refer an image?

  • seetharaman
    July 31, 2011

    Hi Anish 1cm dia (10mm plastic conduit used for electrical wiring).

  • Anish
    July 31, 2011

    Hi Sir,
    What does “1cm plastic former” signifies?
    If i am right, is it the coil core? and 1cm diameter or radius?
    Give me some examples of what to use to figure out

  • seetharaman
    July 29, 2011

    Hi Sarah, Vysakh increase R1 to 10K use 2n2F as coupling capacitor as decoupling is 10nF coupling should be at least 1/5 of this value. use signal from head phone socket of Laptop and use its volume control for modulation level such that transmitted audio signal is clear.

    • charles
      December 10, 2014

      does this cct really work? I want to try it.pls I need necessary. information about it.

  • vysakh
    July 28, 2011

    @sarah , you can use it through a 0.1mfd ceramic filter capacitor. I already checked .
    @seetharaman , this circuit produces some noice and audio quality not good as i expected with condenser mic. I think a pre audio amp shold provide in this circuit.

  • Sarah
    July 28, 2011

    Not for a microphone seetharaman. If i want to send a signal from my laptop. To play music or something. Wouldnt ah headphone female jack work using this same circuit?

  • seetharaman
    July 28, 2011

    Hi Sarah you have to use electret condenser microphone. Moving coil microphone will not work.

  • Sarah
    July 27, 2011

    Can I use a 1/8 inch female headphone jack instead of the microphone?

  • seetharaman
    July 20, 2011

    Hi Rick it is the feed back capacitor for oscillation, without which the circuit will not oscillate.

  • RICK
    July 19, 2011

    Is C3 used for Frequency Stability of the Transmitter??

  • RICK
    July 19, 2011

    Awesome Circuit!! Simple and Fun to Build!!! Yee-Ha!!

  • Jack
    June 30, 2011

    But, i am gettin proper reception within one metre only…. S der any problem with the inductance coil..? Am using a single stranded insulated copper wire… Or any problem wit d antenna? I am using ordinary insulated wire of length 25 to 30 cm… Whether the small increase in length matters a lot?

  • seetharaman
    June 29, 2011

    Hi Jack 50 to 100 feet.

  • Jack
    June 28, 2011

    Hello sir… Thank you… Awesome job… Really great functionality in a compact size…

    But, i request you to specify the reception range… Please post t as soon as possible…

  • Pacific
    April 2, 2011

    sir,if possible you send for me another different circuit of FM transmitter wich uses 9V

  • Pacific
    April 2, 2011

    your circuit is useful and needed by many person’s involved in technologies i need some addition information because me also i want to get knowledge from those.

    thanks

  • YY
    January 27, 2011

    What is the purpose of c3

  • seetharaman
    June 28, 2010

    Yes Anish you can use.

  • Anish
    June 27, 2010

    sir, should we use the ordinary hookup wire for the inductor with or without the insulator over the wire…

  • seetharaman
    June 26, 2010

    Hi Hengilbert yes you can use 2 to 33PF FM radio plastic trimmer capacitor can be used for C2.

  • Hengilbert
    June 26, 2010

    C2 is a trimcap….if it is,can i use 30 or 40?

  • June 9, 2010

    if this is a fm transmitter then what is the receiver

  • seetharaman
    April 20, 2010

    Hi Sam you can use insulated single strand hook up wire which will be around 20SWG, that will be ok.

  • Sam
    April 20, 2010

    Hi… I cant find this wire 24AWG and 18AWG wire in my area… So can you please tell me their alternatives which are easily available in Market.. Please reply..

  • Rashed
    April 13, 2010

    it is very good circuit.i have worked with this circuit.but i used 9V to operate this circuit .thank you.
    student of manarat university.

  • seetharaman
    March 27, 2010

    Hi Jayaprakash these transmitters can operate in VHF range can be fixed in FM Broadcast Band (88 to 108MHz) We can tune first our receiver to a frequecy where there is no broadcast station. Now switch on the above transmitter, with a fibre rod expand or compress the 5 turn coil till you get the feedback howling. Now keep the transmitter near a sound source, which you want to transmit and try to listen by fine tuning the receiver and relax.

  • jaya prakash
    March 26, 2010

    at which freq this circuit operates.
    since there is no variable components, can u tell me freq

  • fii
    September 30, 2009

    information on various components of a miniature FM transmitter

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