const int trigPin = 9;
const int echoPin = 10;
const int redLED = 2;
const int greenLED = 3;
const int yellowLED = 4;


long duration;
int distance;

void setup() {
 
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);

  Serial.begin(9600);
}

void loop() {
 
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);

  distance = duration * 0.034 / 2;

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  if (distance > 250) {
    digitalWrite(redLED, HIGH);
    digitalWrite(greenLED, LOW);
    digitalWrite(yellowLED, LOW);
  } 
  else if (distance >= 100 && distance <= 250) {
    digitalWrite(redLED, LOW);
    digitalWrite(greenLED, HIGH);
    digitalWrite(yellowLED, LOW);
  } 
  else if (distance < 100) {
    digitalWrite(redLED, LOW);
    digitalWrite(greenLED, LOW);
    digitalWrite(yellowLED, HIGH);
  } 
  else {
    
    digitalWrite(redLED, LOW);
    digitalWrite(greenLED, LOW);
    digitalWrite(yellowLED, LOW);
  }

  delay(100); 
}