This circuit was found in a Popular Electronics from the 90s. The counter circuit is not common today. The circuit can be programmed for hourly intervals, according to the values of R4 and C2.
If the input voltage falls below 12 V the LED glows up. Other voltages can be monitored by...
ON Semconductor FFSP0665B 650V 6A SiC Schottky Diodes Available through Mouser Electronics, these...
This adjustable circuit from 0 to 200 nA was found in a 90's EDN. The components can still be...