This is a simple circuit in which the glowing LED can be switched OFF just by a puff. A condenser mic (M1) is used to sense your puff. When the push button S1 is pressed, the transistors Q2 and Q3 wired as latching pair gets activated and drives the LED to glow. The LED remains in this condition. When you puff on the condenser mic, the sound pressure is converted into a voltage signal at its output. This voltage signal will be amplified by the transistor Q1.Since the collector of the Q1 is coupled to the emitter of the latching pair, the pair will stop conducting when ever there is a signal from the condenser mic due to puffing and the LED will go OFF.  The push button switch S1 has to be pressed again to switch the LED ON.

Circuit diagram with Parts list.



  • The circuit can be powered from a 3V battery.
  • The M1 can be a general purpose condenser microphone.
  • The switch S1 can be push button switch.
  • The circuit can be assembled on a good quality PCB or common board.
  • Instead of the LED, you can also try a low power 3V bulb.


  1. this project is really very good.. mine its working good.. i have connected a relay across the led to use for 220 v light bulb..thankyou.

  2. is there any way to replace the LED with say a fan and the circuit operate the same?

  3. Please tell me the values of the condencers/capacitors as 10uf….v.

    • kindly send me details of this CIRCUIT ON MY EMAIL
      thanking you sooo much
      please dear nouman malik

  4. Hi, in the circuit shown in the URL, i need to have 3 or 5 LED glowing instead of 1. kindly help me with the modifications.


  5. Jimmy Svensson

    Why does the latch turn off when q1starts conduct?

  6. if the LED is not switching of try using C1 as 1uF instead of 100pF … worked for me…

  7. seetharaman

    Hi Taimur we will try to publish a suitable circuit.

  8. Can somehow by any means instead of using the LED , I may use this circuit for a 40W bulb? what modifications will I have to do for it ?

  9. Seetharaman

    Hi Aniket Disconnect D1 and C2 and switch on power, LED should not light up. Now push S1 it should come on. Releasing S1 should turn off if this operation is OK, check for the polarity of C2 and D1.

  10. hi!
    Why does the led turns off when the latching pair stops conducting. Even though the switch is still connected.

  11. Shivakumar

    Hey. . . I hav the similar problem . . plz help on this. it’s our 1st mini project, and i don’t wanna fail in that. . . . . .


    for admin. i was try it. but, it doesn’t work. LED only “on” if i staying to press the switch, and led’ll “off” after i relase it. ECM is unfunctionable to off led. can you help? tks


    rangkaian yang unik. bagus, perlu dikembangkan itu.

    the unique circuit. good, that need to improved.

  14. if there is a small changes in the value of the
    components.does it will effect?

  15. what is the application of this circuit in day to day life?

  16. jia jalapan

    can we ask something about the history of Puff to OFF LED circuit?

  17. ThayoSoft

    Very great circuit and very useful for my project.Continue with more interesting posts.Cheers

      • Nouman Nazir Malik

        just check Base Collector and Emmiter

        • Condoriano

          why does not led not turning off? what is the problem?i already checked the transistor many times but the led doesn’t turning off.