This circuit was found in American documentation from the 1960s. The operational amplifier is from that time, but the configuration applies to modern equivalents.
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...