#define ECHOPIN 12            //set pin 12 on the Arduino board as the ECHO pin
#define TRIGPIN 13            //set pin 13 on the Arduino board as the TRIG pin


int delaytime = 100;          //initialize variables for better performance of the code
int duration = 0;             //
int var = 10000;              //needed to convert the output in centimeters
float distance = 0;           //
float spread = 340;           //ultrasonic velocity spread in air in m/s

void setup()
{
  Serial.begin(9600);             //set the Baudrate to 9600, Baudrate - data rate in bits per second for serial data transmission
  pinMode(ECHOPIN, INPUT);        //set the mode on the ECHO pin to INPUT
  pinMode(TRIGPIN, OUTPUT);       //set the mode on the TRIG pin to OUTPUT
}

void loop()
{

  // Start Ranging - Generating a trigger of 10us burst

  digitalWrite(TRIGPIN, LOW);    //wipe the HIGH, just in case
  delayMicroseconds(2);          //..........................
  digitalWrite(TRIGPIN, HIGH);   //send HIGH pulse to the TRIG pin to activate it
  delayMicroseconds(10);         //10 uS length of the HIGH pulse,   at this point the ECHO pin goes to HIGH until it receives the reflected signal
  digitalWrite(TRIGPIN, LOW);    //kill the pulse


  //Distance Calculation

  duration = pulseIn(ECHOPIN, HIGH);        //detects when the ECHO pin goes to HIGH and records the time until it goes back to LOW in uS
  distance = duration*spread/(2*var);       //calculate the distance between the object and the sensor
  Serial.println(distance);                 //print the calculated distance
  delay(delaytime);                         //repeat every *delaytime* milliseconds
}