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 triggers the LED when the monitored battery voltage drops below 9 V for 12 V...
We found this circuit in a Radio Electronics from January 1967. The SCR is already the C106, which...
This power source with silicon diodes at a time when valves were still used was found in Radio...