The circuit shown here doesn't use any moving parts to detect vibration. Rather, a piezo speaker element is used as a sensitive vibration sensor. Curious how it works? The piezo speaker is connected to the input of an op amp operated as a comparator. This operation is achieved by eliminating the usual feedback resistor between the output (pin 6) and the inverting input (pin 2). In operation, tiny vibrations cause the piezo element to generate a small voltage. The LED glows when the voltage exceeds that applied to pin 3 of the op amp by sensitivity control R2. Visit the Jameco Workshop page for complete build instructions.
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