This is the circuit for the HM-10ª, an instrument sold by Heathkit. The circuit is from a Radio Electronics from May 1963. The indication is by an analog instrument.
The battery charger suggested in the figure has its current limited by resistor R1. This component may...
This interesting 80's EDN circuit divides the input pulse frequency by a number given by n...
This circuit was found in a 1969 CQ magazine. It is intended for coupling telephones to radio...