This is a design schematic to sensor the electromagnetic field. This circuit is based or built by 741 IC. This IC is an op-amp. The circuit can detect the field even hidden wrings. This is the figure of the schematic. A 1mH inductor is used for sensing the electric field. The electric field will induce a small voltage in the sensor inductor and th
is induced voltage is amplified by the op amp. The headphone connect at the output of the op amp will give an audio indication of the electric field. For example, the electric field around a main 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. All electrolytic capacitors must be rated at least 15V. The switch S1 can be a slide type ON/OFF switch. The POT R4 can be used to adjust the gain. It is better to have a radial type inductor for L1.