We found this touch control on a Popular Electronics from 1970. The circuit makes use of an integrated of the time. It can be adapted to use modern equivalent components.
Mouser Electronics is now shipping DA14585, a kit for the development of voice remote control...
Found in a 1980s documentation, this circuit uses a photo-Darlington. There must be an optical...
This circuit can operate in a 100 dB range with signals of up to 100 MHz frequencies. Similar...