Note: The schematic diagram shows TN0604N3 MOSFETs as they were available in the parts library and have the same pinout as the 2N7000 specified in the bill of materials. The schematic diagram also shows piezoelectric transducers that were available in the parts library, but any of a wide range of piezoelectric transducers can be used. The capacitor and resistor values are not critical, and a wide range of values can be substituted.