Electromagnetic field sensor circuit


This is a very simple circuit that can be used to sense electromagnetic radiations. The circuit can even detect hidden wrings. A 1mH inductor is used for sensing the electric field. The electric field will induce a small voltage in the sensor inductor and this induced voltage is amplified by the opamp.The headphone connect at the output of the opamp will give an audio indication of the electric field. For example, the electric field around a mains transformer can be heard as a 50 Hz hum. The POT R4 can be used to adjust the gain of the amplifier. By keeping the sensor inductor near to a telephone line, you can even hear the telephone conversations.

Circuit diagram with Parts list.



  • Assemble the circuit on a general purpose PCB.
  • The circuit can be powered from a 9V PP3 battery.
  • It is better to have a radial type inductor for L1.
  • The POT R4 can be used to adjust the gain.
  • The switch S1 can be a slide type ON/OFF switch.
  • The IC1 must be mounted on a holder.
  • All electrolytic capacitors must be rated at least 15V.
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27 Responses to “Electromagnetic field sensor circuit”

  • vaibhav says:

    can u tell us the calculation steps and details about the complete circuit?
    especially calculation regarding inductor value.also can i know how to implement and execute it on multisim or any other software and get the output?

  • Md. Asif Mostafa says:

    can i use 2 680uh inductor in series instead of 1mh.

  • Asif says:

    Can it sence radiation from mobile phones (900,1800,1900 MHz) ? And what is the range of frequencies it can capture?

  • ERIC says:

    what is the voltage rating of the polarized capacitors?Thika Kenya.

  • juti kankana mazumdar says:

    Is C2 an electrolytic or ceramic capacitor?

  • honam says:

    i request circuit electronic magnetic sensor speed&flow

  • Abhishek says:

    Hi.. I am trying to make a pick and place robot using ELECTROMAGNETISM…if you can then please provide me a tutorial to proceed. I need to vary the weight on it.
    waiting for your reply!
    Thank you..

  • shashank gupta says:

    sir, in place of inductor i can use magnetic coils.

    • Seetharaman says:

      Hi Gupta you can try 2 to 3 hundred turns of 32 swg super enamelled copper wire on a 20mm dia plastic bobin, which is normally used for picking up telephone stray magnetic field to amplify the telephonic coversation for a group of people to listen in those days.

      • Ramnarayanan says:

        Sir, Can we use LEDs instead of headphone???If yes then what changes in the circuits would occur???? If NO then what are the requirements of headphone….PLZ reply as soon as possible

    • honam says:

      Hi Looking for electrical circuit design and program a microcontroller for magnetic speed sensor or the way I am Thanks

  • Ramnarayanan says:

    Can we use LEDs instead of headphone???If yes then what changes in the circuits would occur???? PLZ reply as soon as possible

  • Nick says:

    Hi, is there a way to also include an LED which would indicate the presence of the EM field ?

  • seetharaman says:

    Hi Aatsh you can use 2 in series nothing wrong.

  • aatish says:

    sir if we use 2 pot of 1M then it will run or not.actully we use 2pot in series in pcb layout.so confusion sir it correct or not

  • seetharaman says:

    Hi Aatish you can use one 1M pot itsely that itself will give sufficient volume. For inductor you have to use only radial type whch can pick up the stray magnetic field. other types may not pick up the field sufficiently to give the indication.

  • aatish says:

    sir can we use 1M of two pot in series combination in the place of 2.2 M pot.and can we use other shape inductor in place of 1mH INDUCTOR. like resistive inductor

  • Rajsree says:

    How does this circuit actually works and i need the gauge specifications of the inductor coil used here

  • Peter says:

    how to calculate the voltage applied on pin2 and 3 mathematically? By using formula’s

  • Howard says:

    Where can I find a 2.2 m pot at R4?

  • rockie says:

    1) how i test to ckt?
    2)can i replace led for hp?
    3)can u show me which terminals of pot i can short?

  • Seetharaman says:

    Hi Naik the inductor picks up the stray magnetic field available in its near visinity and amplifies it through IC 741, which is a variable gain amplifier and feeds it to the head phone for listening. will be useful for finding the route of consealed power wiring at home by listening to 50 / 60Hz power supply frequency.

  • prafulla naik says:

    i want to know how this ckt actually works?

  • Mohammed says:

    I want ask can I test leak from microwave oven.

  • ricardo says:

    Thx a lot it worked really well,Can i use led in place of speaker?

  • Priyankar says:

    i want to ask that radial inductor is not available in my region then there is any other alternative for that…….can you please tell me…..

  • andhik says:

    can you explain the circuit. and what kind of opamp in there? is it e differentiator?
    what should i changes if i want to increase the detection frequency until 6Mhz?