MAX9814 Microphone Amplifier Module

				
					#include <SPI.h>
#include <SD.h>

// Pin definitions
const int micPin = A0;          // MAX9814 OUT connected to this pin
const int pwmPin = 9;           // Amplifier IN connected to this pin
const int recordButtonPin = 2;  // Record button
const int playButtonPin = 3;    // Play button
const int chipSelect = 10;      // SD card CS pin

// Variables
volatile bool recordFlag = false;
volatile bool playFlag = false;
File audioFile;

void setup() {
  Serial.begin(9600);

  // Initialize SD card
  if (!SD.begin(chipSelect)) {
    Serial.println("SD card initialization failed!");
    return;
  }
  Serial.println("SD card initialized successfully.");

  // Set pin modes
  pinMode(recordButtonPin, INPUT_PULLUP);
  pinMode(playButtonPin, INPUT_PULLUP);
  pinMode(pwmPin, OUTPUT);

  // Set PWM frequency to 62.5kHz to reduce noise
  // Timer1 configuration, works with pins 9 and 10 on Uno
  TCCR1A = _BV(COM1A1) | _BV(COM1B1) | _BV(WGM10); // 8-bit fast PWM
  TCCR1B = _BV(CS10);                              // No prescaling

  // Set up interrupts, trigger when button is pressed (grounded)
  attachInterrupt(digitalPinToInterrupt(recordButtonPin), setRecordFlag, FALLING);
  attachInterrupt(digitalPinToInterrupt(playButtonPin), setPlayFlag, FALLING);

  Serial.println("System ready. Press buttons to start recording or playing.");
}

void loop() {
  if (recordFlag) {
    recordFlag = false;
    recordAudio();
  }

  if (playFlag) {
    playFlag = false;
    playAudio();
  }
}

// Interrupt service routines
void setRecordFlag() {
  // Simple debounce, can add delay or software debounce if button is unstable
  if (digitalRead(recordButtonPin) == LOW) {
    recordFlag = true;
  }
}

void setPlayFlag() {
  if (digitalRead(playButtonPin) == LOW) {
    playFlag = true;
  }
}

// Recording function
void recordAudio() {
  Serial.println("Starting recording...");
  // Delete old file if it exists
  SD.remove("audio.raw");
  audioFile = SD.open("audio.raw", FILE_WRITE);

  if (!audioFile) {
    Serial.println("Failed to create file!");
    return;
  }

  unsigned long startTime = millis();
  // Record for 5 seconds, can modify as needed
  while (millis() - startTime < 5000) {
    // Read analog value (0-1023) -> 10 bits
    int sample = analogRead(micPin);
    // Store 10-bit data as 2 bytes (high byte and low byte)
    byte highByte = (sample >> 8) & 0xFF; // Get high 2 bits
    byte lowByte = sample & 0xFF;         // Get low 8 bits
    audioFile.write(highByte);
    audioFile.write(lowByte);
    // Short delay to control sample rate, approximately 9.6kHz
    delayMicroseconds(100);
  }

  audioFile.close();
  Serial.println("Recording finished.");
}

// Playback function
void playAudio() {
  Serial.println("Starting playback...");
  audioFile = SD.open("audio.raw");

  if (!audioFile) {
    Serial.println("Failed to open file!");
    return;
  }

  // Read file and output to PWM
  while (audioFile.available()) {
    // Read 2 bytes and reconstruct 10-bit sample
    byte highByte = audioFile.read();
    byte lowByte = audioFile.read();
    int sample = (highByte << 8) | lowByte;
    // Map 10-bit sample to 8-bit PWM (0-255)
    // Shifting right by 2 bits is equivalent to dividing by 4, 1023/4=255.75 -> 255
    analogWrite(pwmPin, sample >> 2);
    // Delay to match recording sample rate
    delayMicroseconds(100);
  }

  audioFile.close();
  // Stop PWM output after playback to mute
  analogWrite(pwmPin, 0);
  Serial.println("Playback finished.");
}