Machine Vibration Controls Hour Meter
designed by David Johnson, P.E.

This hobby circuit allows an off-the-shelf battery powered digital hour meter to be turned on and off, according to a machine's operation, without requiring a direct electrical connection to the machine. Machine vibrations are detected by an off-the-shelf piezoelectric wafer. The wafer is normally used as a sound generator.  The wafer is glued to the bottom of the plastic box containing the hobby circuit and hour meter. The box can then be positioned where vibrations from the machine being monitored are high. The 3v power need by the circuit could be tapped from the hour meter's own lithium battery or from a separate 3v lithium battery. The circuit only draws about 1.5uA, so a 250mA-hr battery would power the circuit for about 10 years.  This electronic circuit was published by me in the January 16 issue of EDN magazine in 1997.