This shield circuit with an optical coupler was found in an 90s EDN. The circuit can be used with voltages from 0 to 600 V with the indicated component values.
This circuit can be used to activate the lamp when it gets dark. We found the circuit in old...
This simple circuit applies to any sensitive SCR. We found it in 1982 Maplin documentation. ...
This circuit is from an old documentation but still current for assembly. Just use BC548 instead...