This circuit can be used in measurement bridges. We found it in the September 1995 Electronics Now magazine. The meter can be from 50 uA to 1 mA and the power supply is simple.
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...