Sound level sensors

Electret Microphone Sensor #

The BOB-09964 breakout board couples a small electret microphone (100Hz-10kHz) with a 60x mic preamplifier to amplify the sounds of voice, claps, door knocks or any loud enough to be picked up by a microcontroller’s analog-to-digital converter.

The Electret Mic Breakout translates amplitude (not volume) by capturing sound waves between two conducting plates (one a vibrating diaphragm and the other fixed) in the microphone and converting them into electrical waves. These electrical signals are then amplified and picked up by your microcontroller’s ADC.


Documentation for this sound sensor is available here.

Code example #

We will simply use analog pin A0 to get sound level. Calibration is necessary to have adequate value for SENSITIVITY depending on your application.

 *  Program:  MIC Sensor tester
 *  Description: print audio volume level to serial. Print "Sound" on loud sound.

#define AUDIO_READ_PIN A0 // Analog pin 0 to read the output of the sensor
#define SENSITIVITY 850  

void setup(){
  Serial.begin(115200); // initialize the serial port

void loop(){
  int sound_wave =   analogRead(AUDIO_READ_PIN);
  if (sound_wave > SENSITIVITY) {  // On loud sound
  delay(100); // ms

Here is a more elaborated code which uses an interrupt to sample at 4kHz. The byte stream can be considered as an SPL stream that can be injected (or saved) into a player. It requires the TimerOne library.

#include <avr/io.h>
#include <stdio.h>
#include <avr/sleep.h>
#include "TimerOne.h"

uint16_t val ;
uint8_t val8bit ;
void uart_putbyte (uint8_t c)
  loop_until_bit_is_set(UCSR0A, UDRE0); // check that UART is available
  UDR0 = c ; // copy character in UART

void setup()
  //Serial.begin(125000); // UART speed to transmit at 64 000 bit/s
  Serial.begin(38400); // for 4000Hz sampling so requires only 32000bps
  Timer1.initialize(250); // timer initialisation
  Timer1.attachInterrupt(callback); // callback function to be called

void callback ()
    val = analogRead(8) ; // A-D conversion
    val8bit = ((val >> 2) ) ; // into 8-bit sample
    uart_putbyte (val8bit) ; // send to UART

void loop()
  // do almost nothing
  delay (1000);
The raw source of the simple sketch example is visible here.


2018 - Muhammad Ehsan, Mamour Diop & Congduc Pham