#define echoPin   5
#define trigPin   4
#define ledMerah  9
#define ledKuning 8
#define ledHijau  7

void setup() {
  Serial.begin(115200);

  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  pinMode(ledMerah, OUTPUT);
  pinMode(ledKuning, OUTPUT);
  pinMode(ledHijau, OUTPUT);

  digitalWrite(ledMerah, LOW);
  digitalWrite(ledKuning, LOW);
  digitalWrite(ledHijau, LOW);
}

float readDistanceCM() {
  // trigger 10us
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // echo (timeout 30 ms)
  unsigned long duration = pulseIn(echoPin, HIGH, 30000UL);
  if (duration == 0) return NAN;          // di luar jangkauan
  return duration * 0.0343f / 2.0f;       // cm
}

void setLED(bool r, bool y, bool g) {
  digitalWrite(ledMerah,  r ? HIGH : LOW);
  digitalWrite(ledKuning, y ? HIGH : LOW);
  digitalWrite(ledHijau,  g ? HIGH : LOW);
}

void loop() {
  float distance = readDistanceCM();

  Serial.print("Jarak: ");
  if (isnan(distance)) {
    Serial.println("Out of range");
    setLED(false, false, false);
  } else {
    Serial.print(distance, 1);
    Serial.println(" cm");

    if (distance < 50.0) {          // air tinggi
      setLED(true, false, false);   // merah
    } else if (distance < 100.0) {  // air sedang
      setLED(false, true, false);   // kuning
    } else {                        // air rendah
      setLED(false, false, true);   // hijau
    }
  }

  delay(200);
}