The integrated circuit used in this application is uncommon today. The circuit is from American documentation from the 1980s. It can be changed to use more modern equivalent components.
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...