int TRIG = 8;
int ECHO = 9;
int relay = 12;
int distance;
long duration;

void setup() {
  Serial.begin(115200);
  pinMode(ECHO, INPUT);
  pinMode(TRIG, OUTPUT);
  pinMode(relay, OUTPUT);
}

void loop() {

  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  duration = pulseIn(ECHO, HIGH);
  distance = (duration/2)/29.1;

  Serial.print("Distance :");
  Serial.print(distance);
  Serial.print(" cm\n");

  if(distance < 15){
    digitalWrite(relay, HIGH);
  }
  else{
    digitalWrite(relay, LOW);  
  }
}