Using a 74123 TTL this circuit was found in the Radio Elecronics magazine of June 1975. The power supply must be 5 V. The capacitor determines the activation time.
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...