This board uses a 555 timer configured as a one-shot to provide a clean digital pulse to a microcontroller. You can connect a piezo disc to the two TRG pins, vcc, and ground and the output pin will give you a 20msec pulse when the piezo is struck. There's an npn transistor on the input so it can be triggered on a positive pulse. This circuit would allow you to connect a piezo to your arduino or other 5V microcontroller project.
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