This is the circuit diagram of a very sensitive electromagnetic field sensor which can sense electromagnetic field from 40Hz to 140Hz. The low noise opamp LF351 and associated components forms the pick-up section. 1uH coil L1 is used for sensing the field and the IC1 performs the necessary amplification. If the picked electromagnetic field is in the audio frequency range, it can be heard through the head phone Z1.There is also a meter arrangement for accurate measuring of the signal strength. Transistor Q1 performs additional amplification on the picked signal in order to drive the meter.
- The circuit can be assembled on a Vero board.
- Use a 9V PP3 battery for powering the circuit.
- IC1 must be mounted on a holder.
- Z1 can be a common walkman head phone.
- Switch S1 is the ON/OFF switch.
- All electrolytic capacitors must be rated at least 10V.