This circuit can be adjusted between 0.2 and 2 V to trigger with chosen voltages comparing them with the input voltages. We found it in a 1967 documentation.
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...