INMP441 microphone

// INMP441 microphone example for Arduino Uno
//
// Note: The Arduino Uno (AVR) does not have a built-in I2S peripheral or
// a standard preinstalled I2S library, so this sketch demonstrates a simple
// software-based read of the microphone clock/data lines using direct pin reads.
// This is not a full audio recorder, but it is a beginner-friendly example that
// compiles on Uno and shows how to detect microphone activity.

#include <Arduino.h>

const byte PIN_BCLK = 2;   // SCK on the INMP441
const byte PIN_LRCLK = 3;  // WS on the INMP441
const byte PIN_DATA = 4;   // SD on the INMP441

volatile bool lastBclk = LOW;

uint32_t readOneI2SSample() {
  // Wait for a rising edge on BCLK, then sample DATA.
  bool current = digitalRead(PIN_BCLK);
  while (current == lastBclk) {
    current = digitalRead(PIN_BCLK);
  }
  lastBclk = current;

  uint32_t sample = 0;
  for (int i = 0; i < 24; i++) {
    // Wait for next clock edge
    bool clk = digitalRead(PIN_BCLK);
    while (clk == lastBclk) {
      clk = digitalRead(PIN_BCLK);
    }
    lastBclk = clk;

    sample <<= 1;
    if (digitalRead(PIN_DATA)) {
      sample |= 1;
    }
  }
  return sample;
}

void setup() {
  Serial.begin(115200);

  pinMode(PIN_BCLK, INPUT);
  pinMode(PIN_LRCLK, INPUT);
  pinMode(PIN_DATA, INPUT);

  Serial.println("INMP441 microphone demo started");
  Serial.println("L/R connected to GND selects the left channel.");
  Serial.println("Speak near the microphone and watch the values change.");
}

void loop() {
  // The INMP441 sends 24-bit audio data synchronized to BCLK/WS.
  // On an Uno this software example is only suitable for basic learning.
  uint32_t raw = readOneI2SSample();

  // Convert to signed-ish 24-bit range for display.
  int32_t sample = (int32_t)(raw & 0x00FFFFFF);
  if (sample & 0x00800000) {
    sample |= 0xFF000000;
  }

  long magnitude = labs(sample);

  Serial.print("Raw: ");
  Serial.print(sample);
  Serial.print("  Magnitude: ");
  Serial.println(magnitude);

  delay(20);
}