We found this circuit in the May 1996 Electronics Now magazine. The relay must have a voltage according to the circuit power supply and a trigger current of no more than 50 mA.
This simulation shows how to use an operational amplifier as a voltage comparator. The sample uses the...
This circuit automatically activates the relay when the phone is answered, closing the record...
This car alarm was found in an American '80s documentation. The circuit automatically activates...