I have a CODEC circuit with a AUX audio output. Is it possible to connect that output back to the ESP32 and transmit to a Bluetooth speaker using the ESP32-A2DP library?

If so, would this be the bones of the program:

  Streaming of sound data with Bluetooth to other Bluetooth device.
  We generate 2 tones which will be sent to the 2 channels.
  Copyright (C) 2020 Phil Schatzmann
  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  GNU General Public License for more details.
  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
#include "BluetoothA2DPSource.h"
#include <math.h> 

#define c3_frequency  130.81

BluetoothA2DPSource a2dp_source;

// The supported audio codec in ESP32 A2DP is SBC. SBC audio stream is encoded
// from PCM data normally formatted as 44.1kHz sampling rate, two-channel 16-bit sample data
int32_t get_data_frames(Frame *frame, int32_t frame_count) {
    static float m_time = 0.0;
    float m_amplitude = 10000.0;  // -32,768 to 32,767
    float m_deltaTime = 1.0 / 44100.0;
    float m_phase = 0.0;
    float pi_2 = PI * 2.0;
    // fill the channel data
    for (int sample = 0; sample < frame_count; ++sample) {
        float angle = pi_2 * c3_frequency * m_time + m_phase;
        frame[sample].channel1 = m_amplitude * sin(angle);
        frame[sample].channel2 = frame[sample].channel1;
        m_time += m_deltaTime;

    return frame_count;

void setup() {
  a2dp_source.start("LEXON MINO L", get_data_frames);  

void loop() {
  // to prevent watchdog in release > 1.0.6


Right now, as a proof of concept, I just bought an off the shelf Bluetooth transmitter:

enter image description here

So, I want to get rid of the off the shelf Bluetooth transmitter to hopefully feed the audio into the ESP32 to transmit instead.

  • \$\begingroup\$ I think you’d want to use an audio codec board, not the midi synth board you’ve shown. \$\endgroup\$
    – Kartman
    Aug 1, 2023 at 22:29
  • \$\begingroup\$ The synth board shown has built-in musical instrument sounds which are used. The application is not music, but instead just emitting different rudimentary tones. \$\endgroup\$
    – adamaero
    Aug 2, 2023 at 13:11

2 Answers 2


According to the A2DP Source (Music Sender), yes it is possible.

You need to set the Bluetooth device name (sink) that you want to connect to and a callback that can supply PCM audio data to be sent.

This feature looks to have been added in the September 2023 release.


The ESP32 ADC is not suitable for any serious audio signals, but it can sample audio at a very low quality. You will need a separate codec board to digitise your audio if you want to listen to music.

See the answers in ESP32 ADC not good enough for audio/music?

  • \$\begingroup\$ The audio is rudimentary sounds, not music. I'm mainly wondering if the ESP32 has the capability to be fed these sounds and transmit them via Bluetooth. \$\endgroup\$
    – adamaero
    Aug 2, 2023 at 13:12
  • \$\begingroup\$ That may work, if you don't do those things simultaneously - activating Bluetooth will probably use too much processing power to sample the audio effectively. Sampling first and transmitting later may work. \$\endgroup\$
    – Paul
    Aug 2, 2023 at 13:46
  • \$\begingroup\$ Aw, ok. It needs to be in real time and the device is battery powered. \$\endgroup\$
    – adamaero
    Aug 2, 2023 at 13:47

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