This circuit has an interface for a multimeter or electronic voltmeter. We found it in a 90s Electronic Engineering. The sensor is an unusual component today.
If the input voltage falls below 12 V the LED glows up. Other voltages can be monitored by...
Found in an old Popular Electronics, this circuit warns when a remote lighting system is not...
This generator is more complete than the previous one, being able to generate pulses as indicated...