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 circuit operates at a voltage of 1.3 V from a single mercury cell. We found in an old...
Found with variations on this site, this circuit was taken from an American documentation from the...
This brightness control for incandescent lamps or engine speed has been found in a 1970 English...