HSRW EOLab Students Wiki

This code monitors the sound intensity using an LM393 sensor connected to an Arduino UNO board. The used sensor has only a digital output. Therefore, the number of times the sensor detects a sound is summed up over a sampling time called “SAMPLE_TIME”. Then the sum called “sampleBufferValue” is printed on a Serial Monitor (laptop) and visualized with the Serial Plotter. Additionally, the code allows communication with a LED to provide a visual alarm if the “sampleBufferValue” surpasses a preset Threshold. Regarding the digital outputs, 0 means silence and 1 means noise.

Detailed explanation is given in the video tutorial

 const int OUT_PIN = 12;          // The OUTPUT of the sound sensor is connected to the digital pin D12 of the Arduino 
 const int SAMPLE_TIME = 10;      // The sampling time in milliseconds,  can be set differently if required
 const int Threshold = 90;       // Threshold on decibel value for LED switching ON, the value has been optimized with respect to the used sampling time (900 cumulative digital counts ≈ 90 dB from "Schall")

 unsigned long millisCurrent;     // current time
 unsigned long millisLast = 0;    //previous time
 unsigned long millisElapsed = 0; // difference between current time and previous time (time interval)

 int sampleBufferValue = 0;       // initiate the sum of digital outputs over the sampling time
 int led = 8;                    // LED on pin 4 of Arduino
 int dB = 0;                     //initiate sound intensity dB value

void setup() {

  Serial.begin(9600);           //Arduino starts serial communication with baud rate 9600
  pinMode(led,OUTPUT);          // the LED is connected as output for alarm purpose
 
}

void loop() { 

  millisCurrent = millis();                    //the current time is assigned to the dedicated variable
  millisElapsed = millisCurrent - millisLast; //the elapsed time is updated 
  
  if(digitalRead(OUT_PIN) == HIGH){          //HIGH means noise
   
  sampleBufferValue++;                       //increments the sum variable by 1
  }
   if (millisElapsed > SAMPLE_TIME) {       //if the elapsed time surpasses the sampling time, print the sampleBufferValue and test threshold for alarm
   
   dB = 0.0666 *(sampleBufferValue) + 30.223; //linear regression to calculate the decibel value based of the rough calibration of the sensor response 
  Serial.println(dB);                        // print decibel values on the Serial Monitor 
  Serial.print("dB");                        // print sound unit decibel
  
  
   if (sampleBufferValue > Threshold) {     // test if the threshold is surpassed 
  
    digitalWrite(led, HIGH);                //blink LED 2 ms ON and 1 ms OFF
    delay(2);
    digitalWrite(led, LOW);
    delay(1);
  }
  
  digitalWrite(led, LOW);                  // the LED is turned off to be ready for the next sample
  sampleBufferValue = 0;                   // re-initialization of the  sampleBufferValue variable for the new sampling time
  millisLast = millisCurrent;              // update the previous time to be the start for the next sample
  }
}