ULTRASONIC

#define echo 12
#define trig 13
void setup() {
  // put your setup code here, to run once:
pinMode(trig, OUTPUT);
pinMode(echo, INPUT);
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
 long dur, dis;
  digitalWrite(trig, LOW);
  delayMicroseconds(2);
  digitalWrite(trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(trig, LOW);
  dur = pulseIn(echo, HIGH);
  dis = (dur/2)/29.1;
  Serial.println(dis);
  delay(100);
}