Electrostatic Charge Detector (Electroscope)
Electroscope is a device that is used to detect electrostatic charges.
To reduce AC noise this circuit uses C1, but it will lower the sensitivity a bit. As a voltage divider we use the MPF102 and R1. The divider’s output will be about 4.5V diving a half-scale reading on M1, a 200-uA meter, when the FET’s gate is earth grounded. A negatively charged object such as a plastic comb will give a negative meter deflection. A positively charged object such as cotton-rubbed glass will give a positive deflection from half scale. here is the schematic diagram:
The whole circuit should be in a metal enclosure and short piece of bare wire makes a fine charge collector.