Found in Ferranti's 1968 documentation, this circuit uses a Darlington photo transistor to drive a 12V relay. The circuit can be implemented with modern equivalent components.
When S1 is in 1, the circuit operates with of half the total power applied to the load. When in...
We found this circuit in a technical documentation from Texas Instruments. The circuit can be...
Varicap or varactor is the basic component used in this circuit of an American 80's documentation. The...