This circuit was found in the March 1992 issue of Radio Electronics magazine. The circuit has several adjustments and uses an operational amplifier. Note the supply voltage.
This circuit is from an Italian magazine Radio Elettronica from January 1977. The circuit shows how...
This circuit was suggested by General Electric in documentation from the 80s. SCRs are common...
Found in a Popular Electronics from the 90s, this circuit checks the presence of voltage on a...