MAX98357A Overview

The module needs three I2S signals: BCLK, LRC and DIN. Unlike some digital audio devices, the MAX98357A does not require an MCLK connection.

Wiring

Module Pinout

Arduino Wiring

Arduino provides an I2S library for its SAMD21-based boards. The official Arduino example covers the Arduino Zero, MKR family and Nano 33 IoT.

ESP32 Wiring

The following is a practical example for a conventional ESP32 development board. ESP32 I2S pins can be assigned in software, so other GPIO choices may also be used when suitable for the specific ESP32 board.

Raspberry Pi Wiring

For Raspberry Pi boards using the standard 40-pin GPIO connector:

Code & Testing

Arduino Zero / MKR / Nano 33 IoT Test

In Arduino IDE, install the appropriate Arduino SAMD Boards package through Boards Manager. The I2S library is included with the SAMD core, so a separate MAX98357A library is not required.

Upload this sketch to generate a simple 440Hz square-wave test tone:

#include <I2S.h>

const int SAMPLE_RATE = 8000;
const int TONE_HZ = 440;
const int AMPLITUDE = 500;

const int HALF_PERIOD_SAMPLES =
  SAMPLE_RATE / (TONE_HZ * 2);

int sample = AMPLITUDE;
int sampleCount = 0;

void setup() {
  Serial.begin(9600);
  Serial.println("MAX98357A I2S test");

  if (!I2S.begin(I2S_PHILIPS_MODE, SAMPLE_RATE, 16)) {
    Serial.println("Failed to initialise I2S!");

    while (true) {
      // Stop here if I2S could not start.
    }
  }

  Serial.println("Playing 440 Hz test tone.");
}

void loop() {
  if (sampleCount >= HALF_PERIOD_SAMPLES) {
    sample = -sample;
    sampleCount = 0;
  }

  // Send identical samples to the left and right I2S channels.
  I2S.write(sample);
  I2S.write(sample);

  sampleCount++;
}

Expected Arduino Result

You should hear a continuous tone from the speaker. Sending the same sample to both I2S channels also makes this a useful first test regardless of whether the module is configured for the left channel, right channel or mono mix.

ESP32 Arduino Test

Install the current ESP32 by Espressif Systems board package in Arduino IDE. Current Arduino-ESP32 releases provide the ESP_I2S.h interface used below.

#include <ESP_I2S.h>
#include <math.h>

const int I2S_BCLK = 26;
const int I2S_LRC  = 25;
const int I2S_DOUT = 22;

const uint32_t SAMPLE_RATE = 44100;
const float TONE_HZ = 440.0f;
const int16_t AMPLITUDE = 4000;
const float TWO_PI_F = 6.28318530718f;

I2SClass I2S;

void setup() {
  Serial.begin(115200);
  delay(500);

  I2S.setPins(I2S_BCLK, I2S_LRC, I2S_DOUT);

  if (!I2S.begin(
        I2S_MODE_STD,
        SAMPLE_RATE,
        I2S_DATA_BIT_WIDTH_16BIT,
        I2S_SLOT_MODE_STEREO)) {

    Serial.println("Failed to initialise I2S!");

    while (true) {
      delay(1000);
    }
  }

  Serial.println("Playing 440 Hz test tone.");
}

void loop() {
  static float phase = 0.0f;
  int16_t buffer[128 * 2];

  for (int frame = 0; frame < 128; frame++) {
    int16_t sample =
      (int16_t)(sinf(phase) * AMPLITUDE);

    // Same sample in left and right channels.
    buffer[frame * 2] = sample;
    buffer[frame * 2 + 1] = sample;

    phase += TWO_PI_F * TONE_HZ / SAMPLE_RATE;

    if (phase >= TWO_PI_F) {
      phase -= TWO_PI_F;
    }
  }

  I2S.write(
    (uint8_t *)buffer,
    sizeof(buffer)
  );
}

Expected ESP32 Result

You should hear a steady 440Hz tone. The Serial Monitor at 115200 baud should show that the test has started.

Raspberry Pi Test

Raspberry Pi OS includes a MAX98357A device-tree overlay. On current Raspberry Pi OS installations, edit:

sudo nano /boot/firmware/config.txt

Add:

dtoverlay=max98357a

Save the file and reboot:

sudo reboot

After rebooting, check that the audio device has appeared:

aplay -l

Then run a test tone:

speaker-test -c2 -t sine -f 440

Expected Raspberry Pi Result

You should hear a test tone from the speaker. Press Ctrl+C to stop the test. Older Raspberry Pi OS releases may use /boot/config.txt instead of /boot/firmware/config.txt.

GAIN and SD Pins

For normal first-time testing, leave GAIN and SD at the module's existing configuration.

SD is also the MAX98357A's channel-select input. Its voltage determines left-channel, right-channel or mono-mix operation, while pulling it low shuts the amplifier down. Breakout boards can include their own resistor network on this pin, so leave it at the module default unless you specifically need to change the channel or control shutdown.

Troubleshooting