This untuned circuit uses one of the world's first commercial transistors, the CK722, having been found in a 1966 publication. Equivalent modern types can be used.
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...
Suggested by National Semiconductor, this circuit can be applied to almost any operational...
This circuit was found in Radio Electronics from the 90s. The circuit can generate signals up to...