We found this circuit in a 1966 documentation. The circuit is intended for a door opening system by the headlight of a car. The sensor is a photo-FET, an uncommon component today.
Two operational amplifiers are used in this source obtained in an American documentation...
This circuit is suggested by the Linear Applications Handbook of National Semiconductor, being used...
This simple circuit for headphones or small speakers was found in documentation from the 90s. The...