const int TRIG_PIN=2;
const int ECHO_PIN=4;
const int RELAY_PIN=15;
long duration,distance;
void setup() {
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(RELAY_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}
void loop() {
  distance=getDistanceInCentimeters();
  if(distance <=100)
  digitalWrite(RELAY_PIN, HIGH);
  else
  digitalWrite(RELAY_PIN, LOW);
  Serial.println("Distance= "+String(distance));
  delay(1000);
}
long getDistanceInCentimeters() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  duration=pulseIn(ECHO_PIN,HIGH);
  return(duration * 0.034/2)+1;
}