This circuit was found in an English magazine from 1977. Signal inputs and outputs must be shielded, and the circuit can be powered by battery, since its consumption is low.
This circuit is from an English publication from 1976 but can be easily assembled with BC548...
This configuration, found in many publications, is from an American book from 1981. The power...
The purpose of this circuit is to ensure that an auxiliary 12 V battery continues to supply power...