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.
Found in documentation from the 1980s, this circuit makes use of discrete components of the time....
Found in an EEE this circuit uses FETs of the time and a bipolar one. Current equivalent...
This circuit was obtained from an 80's EDN. The components used are still common. The circuit can be...