Found in an Electronic Design from the 90's, this circuit indicates three voltage levels by activating the LED in 3 modes: off, flashing and on for high voltage.
This circuit was found in an old 1970s telecommunication documentation. It is suitable for...
Suggested by General Electric in a 1967 publication, this circuit makes use of an SCR of the time....
This circuit allows selective relay actuation in the same line according to the applied voltage....