#define TRIGGER 2
#define ECHO 4

void setup() {
  pinMode(TRIGGER, OUTPUT); //define arduino pin
  pinMode(ECHO, INPUT);  //define arduino pin
  Serial.begin(9600); //enable serial monitor

}
void loop() {
  //pulse output
  digitalWrite(TRIGGER, LOW);       //sets high or low voltage to a specific pin
  delayMicroseconds(4);       //pauses the program for a specific amount of time
  digitalWrite(TRIGGER, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIGGER, LOW);
  
  long t = pulseIn(ECHO, HIGH);  //input pulse and save it variable
  
  
  long cm = (t * (1/29.0) )/ 2;     //time convert distance (Speed of sound is 1/29 cm per microsecond)

  String CM = " cm";

 
  Serial.println(cm +CM);     //print serial monitor cm
  Serial.println();           //print space
  delay(100);                 //delay
}