int redled = 13;
int triggerPin = 12;
int echoPin = 11;
float distance;
int duration;

void setup() {
  pinMode(redled, OUTPUT);
  pinMode(triggerPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600);
 
}

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

 duration = pulseIn(echoPin, HIGH);
 distance = duration * (0.034 / 2);

 Serial.print("Distance = ");
 Serial.print(distance);
 Serial.print(" CM");
}