// conect the trig pin digital pin 13
int trig=13;
// conect th ecch pin digital pin 13
int ecch=12;
void setup()
{
  //start serial moniter
  Serial.begin(9600);
  //set pin trig pin  output mode 
  pinMode(trig,OUTPUT);
  //set pin ecch pin input mode  
  pinMode(ecch,INPUT);
}
void loop()
{
  //trig pin off  
  digitalWrite(trig,LOW);
  //wait microsenond 2 
  delayMicroseconds(2);
  //trig pin on 
  digitalWrite(trig,HIGH);
  //wait microsend 10...
  delayMicroseconds(10);
  //pulsein funtion return time in microsecond
  int dt=pulseIn(ecch,HIGH);
  // sount speed in 1 microsend -->0.034
  float s=0.034;
  // use formul distance=speed*time 
  int distance=s*dt/2;
   Serial.print("distance cm=");
    Serial.println(distance);
}