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L84, Electromagnetic Field Detector

This circuit is sensitive to low frequency electromagnetic radiation and will detect for example hidden wiring or the field that encompasses a transformer. Pickup is by a radial type inductor, used as a probe which responds well to low frequency changing magnetic and electric fields. Ordinary headphones are used to for detection. The field that surrounds a transformer is heard as a 50 or 60Hz buzz.


  • IC = UA741

  • Resistors = 22K (2), 10K, 10R

  • Variable resistor = 2.2M

  • Capacitors = 100uf, 220uf, 100nf

  • Inductor coil = 1mH (milihenry)a

  • S1 = on/off Switch

  • Battery 9volt

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