This telephone recording circuit was found in the June 1979 issue of Radio Electronics magazine. The components are common at the time and the power is supplied by the power grid.
This adding amplifier with the operational LM324 is from the SGS integrated circuits manual of...
This circuit measures the conductivity of a saline solution, which is affected by the electrolysis effect....
This circuit activates one of the selected circuits with a touch of a switch, keeping it...