This simple circuit is used to detect variations in electromagnetic fields around us. It based on an instrumentation amplifier INA122 for Texas instrument. As sensing element, the detector is equipped with Inductor (100uH-1mH). The output is routed out to oscilloscope through a BNC connector. A 9v battery is used to power the circuit.
To detect the EMF, just move this probe near electronics appliance that produce EMF like PSU, soldering station, Wireless router etc. and you will see the waveform and its frequency on Oscilloscope. Tuomas Nylund said that this circuit is not designed to be a scientific instrument or a tool for serious work. It’s just a fun toy. Download design file: emf-probe.zip