This 1980s documentation circuit uses a 741 in a different high-speed comparator configuration. The feed must be symmetrical. The diode is general-purpose.
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...