This optical coupler for short distances is powered by 12 V which is the voltage of the lamp and the relay. The circuit can also use emitting LEDs and the phototransistor can be of any type.
This circuit was found in Radio Electronics from the 90s. The components used are common, and the...
This circuit was found in an American publication called Ham Radio. The circuit uses still current...
This circuit was obtained from a 1997 publication. It is an alarm that has a lock and a bistable...