Abstract: A mechanical-electrical transducer producing an electric signal upon depression of a spring, such as a pushbutton. A piezoelectric element is held in contact with a snap-action spring, and bends when the spring snaps thus producing an electric signal.

Abstract: A liquid level sensor for determining the liquid level in a container includes an oscillator having a feedback path including first and second piezoelectric elements mounted in a turning fork arrangement to provide a first mechanical coupling path between said elements across one end of the turning fork. This first coupling path provides a first feedback signal of one given phase. A second mechanical coupling path between said elements is provided only via the liquid when the liquid is present to a level sufficient to immerse the piezoelectric elements. The second coupling path, when present, provides a second feedback signal of opposite phase to the first feedback signal. The presence or absence of the second feedback signal determines the oscillation or non-oscillation condition of the oscillator.