underTheHood.ino

// cricial audio bits taken from https://github.com/espressif/esp-idf/blob/master/examples/bluetooth/bluedroid/classic_bt/a2dp_sink/main/main.c

// bluetooth, config, discover and audio
#include "esp_bt_main.h"
#include "esp_bt_device.h"
#include "esp_gap_bt_api.h"
#include "esp_a2dp_api.h"


// the audio DAC and amp configuration. 
#include "driver/i2s.h"


// the callback(processes bluetooth data).
// this is the most important function. 
void bt_data_cb(const uint8_t *data, uint32_t len){
   // number of 16 bit samples
   int n = len/2;
   
   // point to a 16bit sample 
   int16_t* data16=(int16_t*)data;
   
   // create a variable (potentially processed) that we'll pass via I2S 
   int16_t fy; 
   
   // Records number of bytes written via I2S
   size_t i2s_bytes_write = 0;

   for(int i=0;i<n;i++){
    // put the current sample in fy
    fy=*data16;
    
    //making this value larger will decrease the volume(Very simple DSP!). 
    fy/=1;
    
    // write data to I2S buffer 
    i2s_write(I2S_NUM_0, &fy, 2, &i2s_bytes_write,  10 );
    
    //move to next memory address housing 16 bit data 
    data16++;
   }
}


void setup() {

  // i2s configuration
  static const i2s_config_t i2s_config = {
    .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 = static_cast<i2s_comm_format_t>(I2S_COMM_FORMAT_I2S|I2S_COMM_FORMAT_I2S_MSB),
    .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1, // default interrupt priority
    .dma_buf_count = 8,
    .dma_buf_len = 1000,
    .use_apll = false,
    .tx_desc_auto_clear = true
  };
  
  // i2s pinout
  static const i2s_pin_config_t pin_config = {
    .bck_io_num = 26,//26
    .ws_io_num = 27,
    .data_out_num = 25, //
    .data_in_num = I2S_PIN_NO_CHANGE
  };
  
  // now configure i2s with constructed pinout and config
  i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
  i2s_set_pin(I2S_NUM_0, &pin_config);
  i2s_set_clk(I2S_NUM_0, 44100, I2S_BITS_PER_SAMPLE_16BIT, I2S_CHANNEL_STEREO);
  i2s_set_sample_rates(I2S_NUM_0, 44100);
  
 // set up bluetooth classic via bluedroid
  btStart();
  esp_bluedroid_init();
  esp_bluedroid_enable();

 
  // set up device name
  const char *dev_name = "ESP_SPEAKER";
  esp_bt_dev_set_device_name(dev_name);

  // initialize A2DP sink and set the data callback(A2DP is bluetooth audio)
  esp_a2d_sink_register_data_callback(bt_data_cb);
  esp_a2d_sink_init();
  
  // set discoverable and connectable mode, wait to be connected
  esp_bt_gap_set_scan_mode(ESP_BT_SCAN_MODE_CONNECTABLE_DISCOVERABLE); 

}
void loop() {
  // put your main code here, to run repeatedly:
  delay(1000);
}