int LedRed=15;
int Ledyellow=2;
int Ledgreen=4;
#define trigPin 18
#define echoPin 19
void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(LedRed, OUTPUT);
  pinMode(Ledyellow, OUTPUT);
  pinMode(Ledgreen, OUTPUT);

  digitalWrite(LedRed, LOW);
  digitalWrite(Ledyellow, LOW);
  digitalWrite(Ledgreen, LOW);  
}

void loop() {
  long duration;float distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);  
  distance = duration / 58.2;
  Serial.print("Distance : ");
  Serial.print(distance);
  Serial.println(".cm ");
  if(distance < 40)
  {
    digitalWrite(LedRed, HIGH);
    delay(500);
    digitalWrite(Ledyellow, LOW);
    digitalWrite(Ledgreen, LOW);
    delay(200);
  }
  else if(distance > 40 && distance <60){ 
    digitalWrite(Ledyellow, HIGH);
    delay(500);
    digitalWrite(Ledgreen, LOW);
    digitalWrite(LedRed, LOW);
    delay(200);

  }
  else if (distance > 60)
    digitalWrite(Ledgreen, HIGH);
    delay(500);
    digitalWrite(Ledyellow, LOW);
    digitalWrite(LedRed, LOW);
    delay(200);

}