We found this circuit in an Electronic Engineering of the 90s. The circuit can be implemented with any logic and next to the diagram the truth table for the indications is given.
The circuit presented is based on a mechanical tuning fork. The circuit is suggested by National...
This source, from a 1982 documentation, uses a triac to control the power and voltage applied to...
This circuit was found in a 1990 Electronics World magazine. The circuit can be mounted today by...