A CMOS oscillator drives a Piezo disk directly but cannot drive a loudspeaker — the disk is the correct low-power output

CMOS oscillator circuits produce a 9V peak-to-peak square wave but supply very little current — insufficient to move a loudspeaker cone, which requires significant current. A Piezo disk is a capacitive load that requires high voltage but minimal current, making it a natural match for CMOS logic output. The result is a quiet, cricket-like sound at audio frequencies; resonance can be amplified by clamping the disk to a resonant surface (cookie sheet, wooden box, balsa wing). This is the technique used in Felix Hess’s insect-like low-power installations. The backwards-output-transformer trick (from Chapter 8) should not be used with CMOS oscillators directly — the Piezo disk connects directly to the output pin.

Examples

Connect a 74C14 oscillator output directly to the hot wire of a Piezo disk; clamp the disk to a matchbox — the buzzing becomes a low-tech cricket. Felix Hess used this in networked swarm installations.

Assessment

A student connects a CMOS oscillator output to a small 4-ohm speaker. Nothing happens. Explain why and describe the correct low-power output device to use instead.