Electromagnetic field sensor circuit

john August 17, 2009 32 Comments


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.
  • Akhil Krishnan
    February 20, 2018

    Sir ,what type of capacitor is use in this circuit?
    Can find weak electric field?

  • vaibhav
    February 23, 2015

    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
    January 16, 2015

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

  • Asif
    November 15, 2014

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

  • ERIC
    September 18, 2013

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

  • juti kankana mazumdar
    August 15, 2013

    Is C2 an electrolytic or ceramic capacitor?

  • honam
    March 10, 2013

    i request circuit electronic magnetic sensor speed&flow

  • Abhishek
    October 21, 2012

    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
    September 5, 2012

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

    • Seetharaman
      September 7, 2012

      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
        October 3, 2012

        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
      April 7, 2013

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

  • Ramnarayanan
    September 4, 2012

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

  • Nick
    July 6, 2012

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

  • seetharaman
    May 1, 2012

    Hi Aatsh you can use 2 in series nothing wrong.

  • May 1, 2012

    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
    April 30, 2012

    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.

  • April 29, 2012

    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
    April 26, 2012

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

  • Peter
    September 3, 2011

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

  • Howard
    May 25, 2011

    Where can I find a 2.2 m pot at R4?

  • rockie
    February 20, 2011

    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
    October 16, 2010

    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
    October 15, 2010

    i want to know how this ckt actually works?

  • Mohammed
    August 4, 2010

    I want ask can I test leak from microwave oven.

  • ricardo
    May 4, 2010

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

  • Priyankar
    February 9, 2010

    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
    May 17, 2009

    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?

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