Using a capacitor as a sensor, this circuit was found in the 1989 Radio Electronics Experimenter magazine. The circuit must be assembled in a shielded box.
The Motorola MOC501O optocoupler has a complete amplifier inside the sensor, enabling the...
This circuit is suggested by the Texas Instruments manual of linear applications of the 90's. The...
This circuit was found in the Radio Electronics magazine of May 1990. The supply voltage depends on...