Streaming from an Analog input

[mohaddeseh-rezaee]

Hi, I am using streaming from analog to stream heart sound signal. my analog voltage is around 1.65v and the max value is 3.3v.
so is it ok if I just change the offset value and maximum? Is there any formula to calculate the offset_value?

ConverterScaler<int16_t> scaler(1.0, -16384, 32767 )

I have just this in the terminal and it seems the code does not work properly.

[ 60665][D][BluetoothA2DPSource.cpp:250] bt_app_work_dispatch(): [BT_API] bt_app_work_dispatch event 0xff00, param len 0
[ 70218][D][BluetoothA2DPSource.cpp:458] bt_app_gap_callback(): [BT_AV] bt_app_gap_callback evt 1
[ 70218][I][BluetoothA2DPSource.cpp:473] bt_app_gap_callback(): [BT_AV] Device discovery failed, continue to discover...
[ 70230][D][BluetoothA2DPSource.cpp:458] bt_app_gap_callback(): [BT_AV] bt_app_gap_callback evt 1
[ 70235][I][BluetoothA2DPSource.cpp:477] bt_app_gap_callback(): [BT_AV] Discovery started.
[ 70665][D][BluetoothA2DPSource.cpp:250] bt_app_work_dispatch(): [BT_API] bt_app_work_dispatch event 0xff00, param len 0
[ 70675][E][BluetoothA2DPSource.cpp:282] bt_app_send_msg(): [BT_API] bt_app_send_msg xQueue send failed
[ 80665][D][BluetoothA2DPSource.cpp:250] bt_app_work_dispatch(): [BT_API] bt_app_work_dispatch event 0xff00, param len 0
[ 80675][E][BluetoothA2DPSource.cpp:282] bt_app_send_msg(): [BT_API] bt_app_send_msg xQueue send failed
[ 83033][D][BluetoothA2DPSource.cpp:458] bt_app_gap_callback(): [BT_AV] bt_app_gap_callback evt 1
[ 83034][I][BluetoothA2DPSource.cpp:473] bt_app_gap_callback(): [BT_AV] Device discovery failed, continue to discover...
[ 83046][D][BluetoothA2DPSource.cpp:458] bt_app_gap_callback(): [BT_AV] bt_app_gap_callback evt 1
[ 83051][I][BluetoothA2DPSource.cpp:477] bt_app_gap_callback(): [BT_AV] Discovery started.
[ 90665][D][BluetoothA2DPSource.cpp:250] bt_app_work_dispatch(): [BT_API] bt_app_work_dispatch event 0xff00, param len 0
[ 90675][E][BluetoothA2DPSource.cpp:282] bt_app_send_msg(): [BT_API] bt_app_send_msg xQueue send failed

thanks in advance

[pschatzmann]

The easiest is just to send the output to a CSVStream and then you can do your calculations:

• calculate the avg value which will go into the offset, this should move the signal center to 0
• after that repeat the output with the centered signal and divide 32767 by the max value which will give the max factor that you can apply w/o having any clipping

[mohaddeseh-rezaee]

thank you, It helped a lot. now I came up with a new issue. I used a sin input and tested streaming. but after about 50s there is no streaming anymore. Do you mind what would be the problem?

starting I2S-ADC...
starting A2DP...
[   595][W][BluetoothA2DPSource.cpp:561] bt_av_hdl_stack_evt(): [BT_AV] Reconnecting to 42:47:ae:76:bf:00
[   596][W][BluetoothA2DPCommon.cpp:41] connect_to(): [BT_AV] connect_to to 42:47:ae:76:bf:00
[   703][E][BluetoothA2DPSource.cpp:726] bt_app_av_state_connecting(): [BT_AV] bt_app_av_state_connecting unhandled evt 4
[ 10702][W][BluetoothA2DPCommon.cpp:41] connect_to(): [BT_AV] connect_to to 42:47:ae:76:bf:00
[ 20703][W][BluetoothA2DPCommon.cpp:41] connect_to(): [BT_AV] connect_to to 42:47:ae:76:bf:00
[ 23617][E][BluetoothA2DPSource.cpp:865] bt_app_rc_ct_cb(): [RCCT] Invalid AVRC event: 6

[mohaddeseh-rezaee]

Code:

/**
 * @file adc-a2dp.ino
 * @author Phil Schatzmann
 * @brief see https://github.com/pschatzmann/arduino-audio-tools/blob/main/examples/adc-a2dp/README.md
 * 
 * @author Phil Schatzmann
 * @copyright GPLv3
* 
 */

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

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

AnalogAudioStream adc;
BluetoothA2DPSource a2dp_source;
/// @brief I added this part
const uint16_t sample_rate = 8000;
int channels = 2;
// The data has a center of around 26427, so we we need to shift it down to bring the center to 0
ConverterScaler<int16_t> scaler(2.4, 0, 2166);

// callback used by A2DP to provide the sound data
int32_t get_sound_data(Frame* frames, int32_t frameCount) {
    uint8_t *data = (uint8_t*)frames;
    int frameSize = 4;
    size_t resultBytes = adc.readBytes(data, frameCount*frameSize);   
    scaler.convert(data, resultBytes);
    return resultBytes/frameSize;
}

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

  // start i2s input with default configuration
  Serial.println("starting I2S-ADC...");
  auto cfgRx = adc.defaultConfig(RX_MODE);
  cfgRx.sample_rate = sample_rate;
  cfgRx.channels = channels;
  adc.begin(cfgRx);
  //adc.begin(adc.defaultConfig(RX_MODE)); default string

  // start the bluetooth
  Serial.println("starting A2DP...");
  a2dp_source.set_auto_reconnect(true); 
  //static std::vector<char*> bt_names = {"B19","RadioPlayer"};
  //a2dp_source.start(bt_names,get_sound_data);
  a2dp_source.start("B19",get_sound_data);
 }

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