#define ECHO_PIN 2
#define TRIG_PIN 3
#define pinRelay 4

float X=400/397.63;

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

void loop() {
  //Generate ultrasonic signal
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  //Read ultrasonic signal
  int duration = pulseIn(ECHO_PIN, HIGH);
  float distance = duration * 0.034 * X / 2;

  Serial.print("Jarak: ");
  Serial.print(distance);
  Serial.println(" CM");

  if(distance < 20)
  {
    Serial.println("Merah (Mati)");
    digitalWrite(pinRelay, LOW);
  }
    else if (distance >= 100 )
  {
    Serial.println("Hijau (Nyala)");
     digitalWrite(pinRelay, HIGH);
  }
    
  else{
    Serial.println("Kuning");
  }
  
  delay(500);
}