#define TRIG_PIN D2
#define ECHO_PIN D3
#define RELAY_PIN D4

void setup() {
  Serial.begin(9600);
  
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(RELAY_PIN, OUTPUT);
  
  digitalWrite(RELAY_PIN, LOW);
}

long getDistance() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  long duration = pulseIn(ECHO_PIN, HIGH);
  long distance = (duration / 2) / 29.1; // Convert to cm

  return distance;
}

void loop() {
  long distance = getDistance();
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  if (distance < 100) { // Adjust threshold distance as needed
    digitalWrite(RELAY_PIN, HIGH);
  } else {
    digitalWrite(RELAY_PIN, LOW);
  }

  delay(1000);
}