This circuit was found in the June 1991 issue of Radio Electronics magazine. The circuit uses two Hall effect sensors of the time. It can be assembled using modern equivalents.
To operate with high input voltages using a 3-terminal voltage regulator such as the LM340-15, we...
We found this circuit in the October 1988 Radio Electronics magazine. The circuit is still current...
This audio signal relay was found in an American 1980s documentation. The relay is in accordance...