This shield circuit is from an American documentation from 1969. The components can be modified according to the relay and power, and the coupler can be of a modern type.
This low drift or offset circuit is from an 80's documentation. The configuration can be made with...
This circuit has a logarithmic response as a function of the light falling on the sensor. The...
Found in 80's Electronic Engineering, this circuit can tune the frequency to be rejected. The power...