ESP32 Music Player, a ESP32 project

Build a portable Bluetooth music player powered by an ESP32 that streams audio wirelessly from your phone or tablet. The MAX98357A Class-D amplifier drives a speaker with clean, efficient mono sound, while an SSD1306 OLED display shows playback status. A rechargeable 18650 battery with charging module and 5V boost converter provides hours of cordless listening.

This guide includes a complete wiring diagram, parts list with sourcing tips, and ready-to-flash Arduino firmware with Bluetooth A2DP support. Follow the step-by-step assembly instructions to wire the power supply, connect the I2S audio path, and integrate the display. Once programmed, the player pairs instantly with any Bluetooth device and begins streaming.

Wiring diagram

Gather all the parts

Qty	Component
1	MAX98357A I2S Class-D Mono Amplifier Breakout 5 V / 3 W mono I2S-input Class-D mono audio amplifier IC on a compact breakout board. Accepts I2S digital audio input (BCLK, LRC, DIN) and drives a small speaker or transducer directly. No I2C/SPI control bus is needed. The amplifier supply range is 2.5V-5.5V, and the I2S input pins are compatible with 3.3V logic. SD/MODE controls shutdown and channel selection; GAIN selects 3 dB, 6 dB, 9 dB, 12 dB, or 15 dB gain.
1	8Ω Speaker 8 Ω, 1–3 W Generic small 8Ω 0.5-3W loudspeaker (~28mm typical). Pair with an I2S amp (MAX98357A) or class-D amp (TPA3116D2) for usable volume; do not drive directly from a GPIO pin. Audio output for music/voice playback.
1	SSD1306 OLED 0.96 in, 128×64 0.96 inch 128x64 OLED display with I2C interface
1	18650 Li-ion Cell 3.7 V, 2500 mAh 18650 lithium-ion cell, nominal 3.7 V, ~2500 mAh. Common for higher-capacity portable / battery-bank style projects; needs a holder and protection / charger circuit.
1	TP4056 Li-Ion/LiPo charger module with protection USB-C protected, 1 A TP4056 single-cell Li-Ion/LiPo linear charger module, 5V USB input, 1A charge current (programmable). Common variants ship with DW01 protection. Pair with battery_lipo_storage for the cell.
1	MT3608 adjustable 5 V boost converter Set to 5.0 V, ≥1 A continuous Adjustable step-up regulator set to 5.0 V, supplying the ESP32 and audio amplifier from a single-cell lithium-ion battery.

Assemble it in 5 steps

1. Prepare the battery supply

Use one protected 3.7 V 18650 cell in a proper insulated holder. Connect battery_1 positive to charger_1 B+ and battery_1 negative to charger_1 B-.

Use a protected cell and an insulated holder; observe the + and − marks.
Never short, puncture, solder directly to, or charge an unprotected lithium-ion cell.

2. Wire the charger and 5 V converter

Connect charger_1 OUT+ to boost_1 IN+ and charger_1 OUT− to boost_1 IN−. Before connecting the ESP32, power the charger from its USB charging connector and adjust the MT3608 output between boost_1 OUT+ and OUT− to exactly 5.0 V using a multimeter.

The TP4056 IN pads are for charging input only; use its protected OUT pads for the player load.
Do not connect the battery or ESP32 until the boost output has been measured and set to 5.0 V. Higher voltage can damage the ESP32 and OLED.

3. Connect the ESP32, amplifier, and speaker

Connect boost_1 OUT+ to the ESP32 VIN/5V pin and boost_1 OUT− to ESP32 GND. Connect amp_1 VIN to ESP32 VIN/5V, amp_1 GND to ESP32 GND, BCLK to GPIO26, LRC to GPIO25, and DIN to GPIO27. Connect amp_1 SPK+ to speaker_1 POS and amp_1 SPK− to speaker_1 NEG.

Keep the amplifier-to-speaker wires short and use a speaker rated 8 Ω and 1–3 W.
SPK− is an amplified output, not ground. Connect the speaker only between SPK+ and SPK−.

4. Connect the status OLED

Connect oled_1 VCC to ESP32 3V3 and oled_1 GND to ESP32 GND. Connect oled_1 SDA to GPIO21 and oled_1 SCL to GPIO22.

This design expects the usual SSD1306 I2C address 0x3C.
The OLED uses 3.3 V logic and supply in this build.
Do not connect the OLED VCC to the 5 V rail.

5. Power and charge safely

Turn the portable player on by connecting the charged battery. Charge it by supplying 5 V USB to charger_1's input; the TP4056 handles battery charging. The ESP32 will advertise as Schematik Music Player for Bluetooth pairing.

A 2500 mAh cell is estimated at roughly 2.8 hours at a typical loud playback load; runtime varies with volume.
Use Schematik’s Deploy button to flash the firmware.
Do not leave lithium-ion charging unattended or charge inside a sealed enclosure. The MT3608 and amplifier need airflow at high volume.

Review all connections

1. Connections between "amp_1" and "ESP32"

Function	amp_1	ESP32
`power`	VIN	VIN
`ground`	GND	GND
`data`	BCLK	GPIO 26
`data`	LRC	GPIO 25
`data`	DIN	GPIO 27
`data`	SPK+ → 8Ω Speaker POS	EXT
`data`	SPK- → 8Ω Speaker NEG	EXT

2. Connections between "oled_1" and "ESP32"

Function	oled_1	ESP32
`power`	VCC	3V3
`ground`	GND	GND
`i2c`	SDA	GPIO 21
`i2c`	SCL	GPIO 22

3. Connections between "battery_1" and "ESP32"

Function	battery_1	ESP32
`power`	+V → TP4056 Li-Ion/LiPo charger module with protection B+	EXT
`ground`	GND → TP4056 Li-Ion/LiPo charger module with protection B-	EXT

4. Connections between "charger_1" and "ESP32"

Function	charger_1	ESP32
`power`	IN+ → 5 V USB charging connector positive	EXT
`ground`	IN- → USB charging connector ground	EXT
`power`	OUT+ → MT3608 adjustable 5 V boost converter IN+	EXT
`ground`	OUT- → MT3608 adjustable 5 V boost converter IN-	EXT

5. Connections between "boost_1" and "ESP32"

Function	boost_1	ESP32
`power`	OUT+	VIN
`ground`	OUT-	GND

Deploy the firmware

main.cppOpen in Schematik

#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <BluetoothA2DPSink.h>
#include <driver/i2s.h>


// Forward declarations
void showStatus(const char *line1, const char *line2);

constexpr int I2S_BCLK_PIN = 26;
constexpr int I2S_LRC_PIN = 25;
constexpr int I2S_DOUT_PIN = 27;
constexpr int OLED_SDA_PIN = 21;
constexpr int OLED_SCL_PIN = 22;
constexpr uint8_t OLED_ADDRESS = 0x3C;

Adafruit_SSD1306 display(128, 64, &Wire, -1);
BluetoothA2DPSink a2dpSink;

i2s_config_t i2sConfig = {
  .mode = static_cast<i2s_mode_t>(I2S_MODE_MASTER | I2S_MODE_TX),
  .sample_rate = 44100,
  .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
  .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
  .communication_format = I2S_COMM_FORMAT_STAND_I2S,
  .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,
  .dma_buf_count = 8,
  .dma_buf_len = 64,
  .use_apll = false,
  .tx_desc_auto_clear = true,
  .fixed_mclk = 0
};

i2s_pin_config_t i2sPins = {
  .bck_io_num = I2S_BCLK_PIN,
  .ws_io_num = I2S_LRC_PIN,
  .data_out_num = I2S_DOUT_PIN,
  .data_in_num = I2S_PIN_NO_CHANGE
};

void showStatus(const char *line1, const char *line2) {
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.println(F("SCHEMATIK PLAYER"));
  display.drawFastHLine(0, 12, 128, SSD1306_WHITE);
  display.setTextSize(2);
  display.setCursor(0, 22);
  display.println(line1);
  display.setTextSize(1);
  display.setCursor(0, 50);
  display.println(line2);
  display.display();
}

void setup() {
  Serial.begin(115200);
  Wire.begin(OLED_SDA_PIN, OLED_SCL_PIN);
  if (display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDRESS)) {
    showStatus("Bluetooth", "Pair: Schematik Music Player");
  }

  a2dpSink.set_i2s_config(i2sConfig);
  a2dpSink.set_pin_config(i2sPins);
  a2dpSink.start("Schematik Music Player");
  Serial.println("Bluetooth music player ready. Pair with: Schematik Music Player");
}

void loop() {
  delay(1000);
}