This circuit was found in an old Hewlett Packard publication. Its purpose is to activate neon indicator lamps with signals from a switching circuit.
This basic Schmitt trigger was found in an American publication from 1968. The circuit uses...
This circuit is from an American 1964 documentation. Transistors of the time are used, but modern...
This simple circuit uses small speakers for both listening and speaking (microphone). The feeding is...