int echoPin = 0;
int trigPin = 1;
int greenLed = 11;
int yellowLed = 12;
int redLed = 13;

void setup() {
  pinMode(echoPin, INPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(greenLed, OUTPUT);
  pinMode(yellowLed, OUTPUT);
  pinMode(redLed, OUTPUT);
}

float ultrasonik(){  
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  int durasiPantulan = pulseIn(echoPin, HIGH);
  return durasiPantulan * 0.034 / 2; 
}

void loop() {
  float jarak = ultrasonik();
  if(jarak>100){ 
    digitalWrite(greenLed, HIGH);
    digitalWrite(yellowLed, LOW);
  }
  else if(jarak<=100 && jarak>50){ 
    digitalWrite(yellowLed, HIGH);
    digitalWrite(greenLed, LOW);
    digitalWrite(redLed, LOW);
  }
  else if(jarak<=50){ 
    digitalWrite(redLed, HIGH);
    digitalWrite(yellowLed, LOW);
  }
}