This circuit is from 1964 documentation but can be easily implemented based on current components. Input waveforms and detection are shown next to the diagram.
This lock-up alarm circuit was found in a 1990s Radio Electronics magazine. The sensors are...
Found in Elementary Electronics from 1970, this circuit is a toy for generating different types of sound...
This circuit uses two 4001 ports to drive a relay. The circuit is from Electronics Now magazine, July...