int trigPin=4, echoPin=3, buzzerPin=2;
int red=7, yellow=6, green=5;
long duration, distance;

void setup() {
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(red, OUTPUT);
pinMode(yellow, OUTPUT);
pinMode(green, OUTPUT);
pinMode(buzzerPin, 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/2*0.0343;
Serial.print("Distance is ");
Serial.print(distance);
Serial.println(" cm!");

if (distance<=5) {
  digitalWrite(red, HIGH);
  digitalWrite(yellow, LOW);
  digitalWrite(green, LOW);
  digitalWrite(buzzerPin, HIGH);
}

else if (distance<=10) {
  digitalWrite(red, HIGH);
  digitalWrite(yellow, LOW);
  digitalWrite(green, LOW);
  digitalWrite(buzzerPin, HIGH);
  delay(50);
  digitalWrite(red, LOW);
  digitalWrite(yellow, LOW);
  digitalWrite(green, LOW);
  digitalWrite(buzzerPin, LOW);
  delay(50);
}

else if (distance<=20) {
  digitalWrite(red, LOW);
  digitalWrite(yellow, HIGH);
  digitalWrite(green, LOW);
  digitalWrite(buzzerPin, LOW);
}

else if (distance>20) {
  digitalWrite(red, LOW);
  digitalWrite(yellow, LOW);
  digitalWrite(green, HIGH);
  digitalWrite(buzzerPin, LOW);
}

delay(100);
}