This is an interesting configuration of the LM317 voltage regulator found in an EDN from the 90s. The circuit uses an optical coupler and is intended to supply constant current to a sensor resistor.
This simple alarm circuit was found in a 1998 documentation. When the sensors are activated, the...
This circuit was found in an old American documentation. The integrated circuit used is uncommon...
Found in a 90s Electronic Design, this suggestion to have a higher voltage in a fixed regulator...