Microphone INMP441 I2S Omnidirectional Module

Features:

• Low noise
• Low power consumption
• Suitable for various electronic products
• Stereo input capability (Left/Right channels)
• Omnidirectional microphone response
• 24-bit I2S digital output

Principle of Work:

Sampling high-quality audio requires sample rates of 16-40 KHz. While you can use a timer to sample the ADC directly, this is inefficient for ESP32 CPU usage. Instead, the built-in I2S interface reads samples from the ADC directly into memory via DMA buffers in the background, enabling efficient continuous audio capture.

Pinout:

• SCK: Serial clock for I2S interface
• WS: Word select for I2S (frame sync)
• L/R: Left/Right channel select (Low = left channel, High = right channel)
• SD: Serial data output
• VCC: Power supply, 1.8V to 3.3V
• GND: Ground

Channel Selection (L/R pin):

• LEFT – Connect L/R to GND
• RIGHT – Connect L/R to VDD

Applications:

• Noise detectors
• Voice control modules
• Sound recorders
• Activity monitors

Circuit Example with ESP32:

Below is a simple wiring diagram connecting the INMP441 module to an ESP32. Use GPIO numbers for connections, as ESP32 pinouts may vary.

Library:

The ESP32 Arduino core includes an I2S driver library by default, which supports communication with the INMP441 module.

Example Code (Arduino IDE):

// Include I2S driver
#include "driver/i2s.h"

// INMP441 I2S microphone pins
#define I2S_WS 25
#define I2S_SD 33
#define I2S_SCK 32

#define I2S_PORT I2S_NUM_0
#define bufferLen 64
int16_t sBuffer[bufferLen];

void i2s_install() {
  const i2s_config_t i2s_config = {
    .mode = i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX),
    .sample_rate = 44100,
    .bits_per_sample = i2s_bits_per_sample_t(16),
    .channel_format = I2S_CHANNEL_FMT_ONLY_LEFT,
    .communication_format = i2s_comm_format_t(I2S_COMM_FORMAT_STAND_I2S),
    .intr_alloc_flags = 0,
    .dma_buf_count = 8,
    .dma_buf_len = bufferLen,
    .use_apll = false
  };
  i2s_driver_install(I2S_PORT, &i2s_config, 0, NULL);
}

void i2s_setpin() {
  const i2s_pin_config_t pin_config = {
    .bck_io_num = I2S_SCK,
    .ws_io_num = I2S_WS,
    .data_out_num = -1,
    .data_in_num = I2S_SD
  };
  i2s_set_pin(I2S_PORT, &pin_config);
}

void setup() {
  Serial.begin(115200);
  delay(1000);
  i2s_install();
  i2s_setpin();
  i2s_start(I2S_PORT);
  delay(500);
}

void loop() {
  int rangelimit = 3000;
  Serial.print(rangelimit * -1);
  Serial.print(" ");
  Serial.print(rangelimit);
  Serial.print(" ");

  size_t bytesIn = 0;
  esp_err_t result = i2s_read(I2S_PORT, &sBuffer, bufferLen * sizeof(int16_t), &bytesIn, portMAX_DELAY);

  if (result == ESP_OK) {
    int16_t samples_read = bytesIn / sizeof(int16_t);
    if (samples_read > 0) {
      float mean = 0;
      for (int i = 0; i < samples_read; i++) {
        mean += sBuffer[i];
      }
      mean /= samples_read;
      Serial.println(mean);
    }
  }
}

Technical Details:

• Signal-to-noise ratio (SNR): 61 dBA
• Frequency response: 60 Hz – 15 kHz
• Board size: 14 mm diameter, low profile
• Sensitivity: -26 dBFS at 1 kHz, 94 dB input
• Noise floor: -87 dBFS
• Supported sample rates: 44.1 kHz to 48 kHz

Resources:

• Tutorial
• Datasheet

Comparisons:

Omnidirectional microphones like the INMP441 have a wide pickup radius (up to several meters), making them sensitive to multiple voices and background noise. While excellent for informal meetings, short-distance conversations, and remote activities, their sound quality can be lower than single-point microphones unless effective noise reduction is implemented.