Adafruit STEMMA Piezo Driver Amp User guide

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Adafruit STEMMA Piezo Driver Amp

Created by Liz Clark

https://learn.adafruit.com/adafruit-stemma-piezo-driver-amp

Last updated on 2023-09-06 12:01:39 PM EDT

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Overview

Pinouts

• Power Pins

• I/O Pins

• STEMMA Connector

• Terminal Block

• Gain Selector Switch

• Power LED and Jumper

• Signal LED and Jumper

CircuitPython and Python

• CircuitPython Microcontroller Wiring

• Python Computer Wiring

• Python Setup

• CircuitPython Usage

• Python Usage

• Example Code

Python Docs

Arduino

• Wiring

• Example Code

Arduino Docs

Downloads

• Files

• Schematic and Fab Print

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Overview

Piezos make noise when you put an AC voltage across them - and the bigger the

voltage, the louder they are. With your standard 3V logic microcontroller you can

make 3 volts peak to peak (Vpp) with a PWM out, or 6Vpp differential with two

complementary outputs. But what if you want even louder? Or if you're using a piezo

to sense distance using ultrasonic bounces?

We found the nifty PAM8904(), which is an amplifier specifically designed for driving

piezo elements - and unlike audio amplifiers, it's good for up to 300 KHz! It's a

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switched-cap piezo driver that has bridge-tied load (BTL) output and up to 3x voltage

multiplication thanks to a built-in boosting circuit for up to ~13Vpp.

We whipped up a quick breakout in our 2mm JST-PH STEMMA form-factor to make it

easy for anyone who wants to beep their boops very loudly.

Usage is easy: power with 3 to 5VDC on the Vin and GND pins. Then provide a

square wave on the signal pin, from 20Hz to 300KHz - any duty cycle is ok but 50%

will probably work best. There's a dual DIP switch to set the gain: you can set it to off

(zero gain), x1 gain, x2 gain and x3 gain. The output is differential, so 2x gain will give

you 4xVin peak-to-peak across the piezo lines. Connect your piezo to the terminal

block and you're ready to rock.

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Please note: If you are powering the driver from 5VDC, don't set the gain to x3

because the 15V output is higher than the driver is specified for. (Yeah we also sorta

wondered why the chip manufacturer allows it). So if you are using 3.3V power, x3

gain is OK and will give you about 10V out but if you're powering with 5V use 2x gain

max to keep the max voltage at 10V.

Piezo element() and 3-pin JST PH cable() not included! But we stock 'em in the shop

if you want to pick up separately.

Pinouts

Power Pins

VIN - This is the power pin - provide between 2.3 to 5V DC

•

GND - This is common ground for power and logic.

•

I/O Pins

SIG - The signal input pin. Provide a square wave from 20Hz to 300KHz to

•

output to the attached piezo. The signal level does not have to match the power

voltage level

VO+ - The positive output for a piezo.

•

VO- - The negative output for a piezo.

•

STEMMA Connector

The STEMMA connector is located on the left side of the front of the board, to the left

of the Gain DIP switch. You can use a STEMMA JST PH 2mm 3-pin cable to connect

the driver to your microcontroller board, for example this cable() to connect using a

breadboard.

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The STEMMA connector has the following pins:

SIGNAL (white wire) - Signal input pin

•

VIN (red wire) - Power pin, 3-5VDC

•

GND (black wire) - Ground pin.

•

Terminal Block

The terminal block is located on the right side of the front of the board, above the PA

M8904 label on the board silk.

The block has the following terminals:

VO+ - This terminal is towards the top of the board, and is located next to the x1

•

label on the board silk. It is the same as the VO+ pin. Connect the positive wire

on your piezo to this terminal.

VO- - This terminal is towards the bottom of the board and is located next to the

•

PAM8904 label on the board silk. It is the same as the VO- pin. Connect the

negative wire on your piezo to this terminal.

Gain Selector Switch

Gain - The dual DIP switch at the top of the board lets you adjust the gain output

•

from the PAM8904. You can set it to off (zero gain), x1 gain by flipping the x1

switch to ON, x2 gain by flipping the x2 switch to ON and x3 gain by flipping

both the x1 and x2 switches to ON. The output is differential so 2x gain will give

you 4xVin peak-to-peak across the piezo lines.

Please note: If you are powering the driver from 5VDC, don't set the gain to x3

because the 15V output is higher than the driver is specified for. So if you are using 3.

3V power, x3 gain is OK and will give you about 10V out but if you're powering with 5

V use 2x gain max to keep the max voltage at 10V.

If you are powering the driver from 5VDC, don't set the gain to x3 because the

15V output is higher than the driver is specified for.

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Power LED and Jumper

Power LED - On the front of the board, below the JST-PH connector, is the

•

power LED, labeled ON. It is a green LED.

Power LED jumper - In the lower right corner on the back of the board is a

•

jumper for the power LED. It is labeled LED on the board silk. To disable the

power LED, cut the trace on this jumper. To enable it again, solder the pads back

together.

Signal LED and Jumper

Signal LED - On the front of the board, above the JST-PH connector, is the signal

•

LED, labeled Sig. It is a red LED. It will light-up every time a signal is received on

the signal pin.

Signal LED jumper - In the upper right corner on the back of the board is a

•

jumper for the signal LED. It is labeled SIG on the board silk. To disable the

signal LED, cut the trace on this jumper. To enable it again, solder the pads back

together.

CircuitPython and Python

It's easy to use the STEMMA Piezo Driver Amp with Python or CircuitPython, and the p

wmio() module. This module allows you to easily write Python code to control pulse

width modulation (PWM).

You can use this driver with any CircuitPython microcontroller board or with a

computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-for-

Python compatibility library().

CircuitPython Microcontroller Wiring

First wire up a driver to your board exactly as follows along with a piezo element. The

following is the driver wired to a Feather RP2040 using the STEMMA JST-PH

connector:

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Board 3.3V to driver VIN (red wire)

Board GND to driver GND (black wire)

Board pin 5 to driver SIG (white wire)

Driver VO+ to piezo positive (red wire)

Driver VO- to piezo negative (black wire)

The following is the adapter wired to a Feather RP2040 using a solderless

breadboard:

Board 3.3Vtodriver VIN (red wire)

Board GNDtodriver GND (black wire)

Board pin 5todriver SIG (white wire)

Driver VO+topiezo positive (red wire)

Driver VO-topiezo negative (black wire)

Python Computer Wiring

Since there are dozens of Linux computers/boards you can use, we will show wiring

for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux

to see whether your platform is supported(). pwmio() will also need to be

implemented for your board.

Here's the Raspberry Pi wired using the STEMMA JST-PH connector:

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Pi 3.3V to driver VIN (red wire)

Pi GND to driver GND (black wire)

Pi GPIO 5 to driver SIG (white wire)

Driver VO+ to piezo positive (red wire)

Driver VO- to piezo negative (black wire)

Here's the Raspberry Pi using a solderless breadboard:

Pi 3.3V to driver VIN (red wire)

Pi GND to driver GND (black wire)

Pi GPIO 5 to driver SIG (white wire)

Driver VO+ to piezo positive (red wire)

Driver VO- to piezo negative (black wire)

Python Setup

You'll need to install the Adafruit_Blinka library that provides the CircuitPython

support in Python. This may also require verifying you are running Python 3. Since

each platform is a little different, and Linux changes often, please visit the

CircuitPython on Linux guide to get your computer ready()!

pwmio is a built-in module and does not need to be installed separately using pip .

Make sure to check that pwmio is supported on your platform though if you aren't

using something more common like a Raspberry Pi.

CircuitPython Usage

To use with CircuitPython, you need to update code.py with the example script.

Thankfully, we can do this in one go. In the example below, click the Download

Project Bundle button below to download the code.py file in a zip file. Extract the

contents of the zip file, and copy the code.py file to your CIRCUITPY drive. The

example uses built-in modules, so no additionally libraries need to be copied to the CI

RCUITPY/lib folder.

Python Usage

Copy or download the following example to your computer, and run the following,

replacing code.py with whatever you named the file:

python3 code.py

Example Code

# SPDX-FileCopyrightText: 2018 Kattni Rembor for Adafruit Industries # # SPDX-License-Identifier: MIT

import time import board import pwmio

piezo = pwmio.PWMOut(board.D5, duty_cycle=0, frequency=440, variable_frequency=True)

while True: for f in (262, 294, 330, 349, 392, 440, 494, 523): piezo.frequency = f piezo.duty_cycle = 65535 // 2 # On 50% time.sleep(0.25) # On for 1/4 second piezo.duty_cycle = 0 # Off time.sleep(0.05) # Pause between notes time.sleep(0.5)

When you run the example code, you'll hear an ascending C major scale through the

piezo element on a loop. Use the gain DIP switch to adjust the gain for the piezo

element.

Python Note

If you run this example on a Raspberry Pi, you'll see this printed to the serial console

when the code starts running:

Variable Frequency is not supported, continuing without it...

After that you'll hear the tones being played through the piezo element.

Python Docs

Python Docs()

Arduino

Using the STEMMA Piezo Driver Amp with Arduino involves wiring up the adapter to

your Arduino-compatible microcontroller, attaching a piezo element to the driver and

running the provided example code.

Wiring

Wire as shown for a 5V board like an Uno. If you are using a 3V board, like an Adafruit

Feather, wire the board's 3V pin to the driver VIN.

Here is an Adafruit Metro wired up to the driver using the STEMMA JST-PH connector:

Board 5V to driver VIN (red wire)

Board GND to driver GND (black wire)

Board pin 5 to driver SIG (white wire)

Driver VO+ to piezo positive (red wire)

Driver VO- to piezo negative (black wire)

Here is an Adafruit Metro wired up using a solderless breadboard:

Board 5V to driver VIN (red wire)

Board GND to driver GND (black wire)

Board pin 5 to driver SIG (white wire)

Driver VO+ to piezo positive (red wire)

Driver VO- to piezo negative (black wire)

Please note: If you are powering the driver from 5VDC, don't set the gain to x3

because the 15V output is higher than the driver is specified for. If you're powering

with 5V use 2x gain max to keep the max voltage at 10V.

If you are powering the driver from 5VDC, don't set the gain to x3 because the

15V output is higher than the driver is specified for.

Example Code

// SPDX-FileCopyrightText: 2023 Liz Clark for Adafruit Industries // // SPDX-License-Identifier: MIT

#define PIEZO_PIN 5 // Pin connected to the piezo buzzer.

int toneFreq[] = {262, 294, 330, 349, 392, 440, 494, 523}; int toneCount = 8;

void setup() { Serial.begin(115200); Serial.println("Piezo Tone Example"); }

void loop() {

for (int i=0; i < toneCount; i++) { Serial.print("Playing frequency: "); Serial.println(toneFreq[i]); tone(PIEZO_PIN, toneFreq[i]); delay(250); // Pause for half a second. noTone(PIEZO_PIN); delay(50); } Serial.println(); delay(1000);

}

Upload the sketch to your board and open up the Serial Monitor (Tools -> Serial

Monitor) at 115200 baud. You'll see the tone frequencies printed to the Serial Monitor

as they are played through the piezo element. Use the gain DIP switch to adjust the

gain for the piezo element.

Arduino Docs

Arduino Docs()

Downloads

Files

PAM8904 Datasheet()

•

EagleCAD PCB Files on GitHub()

•

Fritzing object in the Adafruit Fritzing Library()

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Adafruit STEMMA Piezo Driver Amp User guide

Specifications and Main Features

Frequently Asked Questions

User Manual