This simple power supply circuit triggers when the light on the LDR reaches the level set on the potentiometer. The circuit is from an Electronics Now from July 1995.
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....