How to save data file into the RAM

To save a data file such as an MP3 audio file into the RAM memory of an Arduino or ESP32 microcontroller, you can follow these steps:

1. Convert the file: First, you need to convert the MP3 file into a byte array in C++. There are many online tools or scripts to do this. You can also use the converter below!
2. Declare the array: In the Arduino/ESP32 code, declare a byte array with the file data:

const byte audioData[] PROGMEM = {
  // MP3 file byte data here
};

3. Use PROGMEM memory: The PROGMEM keyword helps store data in flash memory instead of RAM.
4. Read and use the data: When needed, you can read data from this array.

Notes:

• The RAM and flash memory capacity of microcontrollers is limited. Arduino Uno only has 2KB RAM and 32KB flash, while ESP32 has more (520KB RAM and 4MB flash).
• Audio files are usually quite large, so consider using an SD card for storage if the file is too big.
• For ESP32, you can use SPIFFS (SPI Flash File System) to store larger files.

Simple Example - ESP32 - Arduino

#include <driver/dac.h>

// Sample WAV file data (replace with your own converted audio data)
const unsigned char wav_data[] PROGMEM = {
  // Your WAV file data here
  // This should be 8-bit unsigned PCM data
  128, 135, 142, 149, 156, 163, 170, 177, 184, 191, 198, 205, 212, 219, 226, 233
  // ... more data ...
};

const int wav_size = sizeof(wav_data);
const int sample_rate = 8000;  // Adjust based on your WAV file
const int dac_pin = 25;  // ESP32 DAC1 (GPIO25) or DAC2 (GPIO26)

void setup() {
  Serial.begin(115200);
  dac_output_enable(DAC_CHANNEL_1);  // Enable DAC on GPIO25
}

void loop() {
  playAudio();
  delay(2000);  // Wait 2 seconds before playing again
}

void playAudio() {
  unsigned long start_time = millis();
  for (int i = 0; i < wav_size; i++) {
    unsigned char sample = pgm_read_byte(&wav_data[i]);
    dac_output_voltage(DAC_CHANNEL_1, sample);
    
    // Simple timing control
    while (millis() - start_time < (i * 1000 / sample_rate)) {
      // Wait
    }
  }
}

Explain Code

The above example does the following:

1. Stores a small WAV file as a byte array in PROGMEM.
2. Sets up the DAC on GPIO25 (you can use GPIO26 for DAC2 if preferred).
3. In the playAudio function, it reads each sample from PROGMEM and outputs it to the DAC.
4. Uses a simple timing mechanism to control the playback speed.

Some important notes:

• This example assumes 8-bit unsigned PCM audio data. If your WAV file is in a different format, you'll need to adjust the code accordingly.
• The timing mechanism is simplistic and may not be perfectly accurate. For more precise timing, consider using a timer interrupt.
• The ESP32's DAC is 8-bit, so it's suitable for low-quality audio. For better quality, you might want to consider using an external DAC or a different method like I2S.
• Remember that the ESP32 has limited PROGMEM, so this method is only suitable for very short audio clips.

To use this:

1. Connect a speaker or amplifier to GPIO25 (and ground).
2. Upload the code to your ESP32.
3. The audio clip should play repeatedly with a 2-second pause between plays.

Tags

• Arduino
• Esp32
• IoT