This circuit indicates when the voltage of a 12 V battery is low. With changes, for example, the zener, the circuit can be used to monitor other voltages.
This circuit is from a Harris Semiconductor datasheet from the 80s. However the circuit can be...
Described in an article that taught how to assemble the complete intercom in Radio Electronics magazine...
This circuit indicates when the voltage of a 12 V battery is low. With changes, for example, the...