This simple circuit for a common 110 V power grid was found in a 1980s American documentation. The circuit uses neon lamps as indicators.
Hughes suggests this circuit in a 1968 documentation. The circuit uses old transistors that can be...
Using a single Darlington phototransistor, this circuit drives a highly sensitive relay, for...
This source whose voltage depends only on the zener diode used, can supply currents up to about 3 A....