In my Arduino ESP32-A2DP library I am providing some very simple examples that show how to transform the ESP32 into a A2DP source and transmit sound to a Bluetooth Sink (e.g. some Bluetooth Speakers).

I had quite some questions on how to do this with files, microphones and I2S as input. So I started a small sister project which provides some additional sound tools. I plan to provide plenty of additional examples for some more advances scenarios.

Analog Microphones

The Sketch

Here is an first example sketch that you can use with an analog microphone as sound source:

#include "Arduino.h"
#include "BluetoothA2DPSource.h"
#include "AudioTools.h"

using namespace audio_tools;  

/**
 * @brief We use a mcp6022 analog microphone as input and send the data to A2DP
 */ 

ADC adc;
BluetoothA2DPSource a2dp_source;
// The data has a center of around 26427, so we we need to shift it down to bring the center to 0
FilterScaler<int16_t> scaler(1.0, -26427, 32700 );

// callback used by A2DP to provide the sound data
int32_t get_sound_data(Channels* data, int32_t len) {
    arrayOf2int16_t *data_arrays = (arrayOf2int16_t *) data;
   // the ADC provides data in 16 bits
    size_t result_len = adc.read(data_arrays, len);   
    scaler.process(data_arrays, result_len);
    return result_len;
}

// Arduino Setup
void setup(void) {
  Serial.begin(115200);

  // start i2s input with default configuration
  Serial.println("starting I2S-ADC...");
  adc.begin(adc.defaultConfig());

  // start the bluetooth
  Serial.println("starting A2DP...");
  a2dp_source.start("MyMusic", get_sound_data);  
}

// Arduino loop - repeated processing 
void loop() {
}

I am using the built in ESP32 analog sampling functionality which is available using I2S. For this I provide the ADC class to make it simple to use. The data from the microphone was centered around 26427, so we need to reduce all values by this. This is done with the help of the FilterScaler. You could also amplify the sound (make the sound louder) by using a factor > 1.0

The Hardware

To test it I am using the tiny MCP6022 microphone module.

The MCP6022 is a analaog microphone which operates at 3.3 V

Pin Assignments

Source Code

Both the project and the example can be found on Github.