#define TRIG 5
#define ECHO 18
#define LED_RED 14
#define LED_YELLOW 12
#define LED_GREEN 13
float duration;
int distance;

void setup() {
  pinMode(LED_RED, OUTPUT);
  pinMode(LED_YELLOW, OUTPUT);
  pinMode(LED_GREEN, OUTPUT);
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
  Serial.begin(9600);
}
void loop() {
  digitalWrite(TRIG, LOW);
  delayMicroseconds(5);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  duration = pulseIn(ECHO, HIGH);
  distance = duration * 0.0344 / 2;
  Serial.print(distance);
  Serial.println("cm");
  delay(100);
  if (distance<100) {
    digitalWrite (LED_YELLOW,LOW);
    digitalWrite (LED_GREEN,LOW);
    digitalWrite (LED_RED,HIGH);
  }
  else if (distance<200) {
    digitalWrite (LED_YELLOW,HIGH);
    digitalWrite (LED_GREEN,LOW);
    digitalWrite (LED_RED,LOW);
  }
  else {
    digitalWrite (LED_YELLOW,LOW);
    digitalWrite (LED_GREEN,HIGH);
    digitalWrite (LED_RED,LOW);
  }
  delay(100);
}