This circuit was obtained in an old documentation, but it is still current by the used components. The circuit must be powered by a 12 V regulated power source.
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...