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 obtained from an old American documentation, and practically any general-purpose transistor...
This light relay is powered directly by the power grid by activating a 110 V relay. The LDR is of...
We found this amplifier in a publication of 1990, but it can be mounted today with some exchanged...