Any sensor or piezo capsule can be used as a sensor in this circuit. The integrated circuit is also common in our days and a table of sensor voltage levels.
This circuit is from a 1967 documentation. It consists of a sensor for memories used at the time....
We found this circuit in the November 1992 issue of Radio Electronics magazine. The circuit has...
Found in EEE documentation, this circuit can have the duration and frequency adjusted separately....