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, found in documentation from the 1980s, uses an operational amplifier from that time....
This low frequency sinusoidal oscillator was obtained in documentation from the 1970s. Operational...
This circuit was found in a 1980s documentation. It is intended for remote vibration monitoring...