int trigPin = 11; // Trigger
int echoPin = 12; // Echo
long duration, cm, inches;
int red = 4;
int yellow = 5;
int blue = 6;
int buzzer = 7;
void setup() {
  //Serial Port begin
  Serial.begin (9600);
  //Define inputs and outputs
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(red, OUTPUT);
  pinMode(yellow, OUTPUT);
  pinMode(blue, OUTPUT);
  pinMode(buzzer, OUTPUT);
}
void loop() {

  digitalWrite(trigPin, LOW);
  delayMicroseconds(5);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  pinMode(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);
 
  cm = (duration / 2) * 0.0343;

  if (cm < 20) {
    digitalWrite(red, HIGH);
    digitalWrite(yellow, LOW);
    tone(buzzer, 1000);
    delay(1000);
    noTone(buzzer);
  }
  else {
    digitalWrite(red, LOW);
    digitalWrite(yellow, HIGH);
  }
  Serial.print(cm);
  Serial.print("cm");
  Serial.println();
  delay(250);
}