35mm Piezo Electric Sensor

A piezoelectric sensor or element is a device that uses the piezoelectric effect to convert voltage to vibration and vibration to voltage. This is a piezoelectric disc that picks up sound from musical instruments and other devices. Because it produces analogue output, you can connect it to a comparator circuit to produce digital output, or you can connect it directly to the microcontroller you're using. It is small and reliable enough to handle rough use, making it suitable for many instruments, such as acoustic guitars and drums.