This circuit was obtained in a 90s documentation. However, it can be developed with modern operational amplifiers. The power supply must be symmetrical.
This simple electroscope with bipolar transistors is not the most sensitive, but can detect static...
This oscillator for various frequencies was obtained from a 1980s telecom documentation. The...
This circuit is from a July 1970 Radio Electronics magazine. The sensors are metal probes. The 18 V...