This circuit is from a 1968 documentation using one of the first integrated circuits available at the time, the TAA370. The circuit is powered by 1.3 V using a 200 ohm handset.
This circuit was found in a September 1982 Radio Electronics magazine. It was the type commonly used...
This amplifier for distributing audio signals appears in other articles on this website and even...
Many reed switches can be wired in series to perform na efficient alarm as shoen in the figure....