#455 Piezo Transducers and Buzzers

Exploring techniques for driving piezo transducers and buzzer units for audio output.

Build

Here’s a quick demo..

Notes

Piezoelectric sensors for generating sound are commonly found in two form factors:

indicator (aka buzzer): complete piezoelectric unit including circuit to produce sound
- just requires an applied voltage to produce sound - fixed frequency by default
- may be combined with external circuitry to mix/alter the sound and frequency
transducer: a basic piezoelectric diaphragm/disk
- sometimes called a “passive” buzzer element
- can be used as an input transducer as well as for sound generation
- does not self-oscillate - requires external circuit to produce sound

PiezoBuzzers

Driving Piezoelectric Indicators

Piezoelectric indicators (aka buzzers) are simple voltage-controlled devices. Typically used as alarms or action feedback indicators. They come in a range of forms - from the very cheap suited to breadboard experiments through to quality devices suited to security alarm installations.

Driving a piezoelectric indicator is simple - it just needs a voltage applied.

Common PCB Mount

Available for pennies and ideal for PCB or breadboard prototyping (however I have come across devices with leads that are far too thick to use on a breadboard without damaging it). It is usually OK to even drive a 3-5V component directly from a 20mA-limit GPIO pin

High Volume Alarms

Beefier devices are more suited to serious alarm purposes, for example this 95dB SPL Continuous Sound Beeper

Buzzer Type: Piezoelectric
Sound Pressure Level 95 dB
Rate Voltage: 12V DC
Operating Voltage: 3 - 24V
Max Current Rating 10mA
Frequency 3900±500Hz
Drive Method: Drive Circuit Built in Mounting Holes
Sound: “Di” Continuous

buzzer_alarm1_build

Alarms with Effects

Sometimes the piezo indicator circuit has a built-in effect, like for example this device which emits a beep every half a second or so.

Sound Pressure Level 95 dB
Rate Voltage: 12V DC
Operating Voltage: 3 - 24V

buzzer_alarm2_build

Driving Piezoelectric Transducers

Piezoelectric Transducers require an external oscillator to produce sound output.

A common circuit for turning a Piezoelectric disk into a buzzer uses a low-side switch. Plain piezo disks require a bypass resistor to dump the charge (else no sound will be produced). Additional resistance can be added to limit current and reduce volume.

In the following test circuit, I have a 555 astable oscillator with variable resistor to generate a pulse from about 152 Hz to about 10kHz

The 555 output switches a low-side 2N7000 n-channel FET.

I’ve selected a 10kΩ bypass resistor. Lower values start to attenuate the output.

A 2.2kΩ series resistor limits current without much impact on volume.

Breadboard