In this circuit the triac conducts when switch S1 is opened. We found it in the October 1987 Radio Electronics magazine. The triac is controlled according to the load.
This circuit was found in an American 1980s documentation. Equivalent operational amplifiers can be...
This busy line indicator is very simple, serving for analog lines. The supply is made by two...
This simple circuit uses a 200 uA microammeter of the type found as VU, being able to measure...