For use with the Ultrasonic Ranging Module HC-SR04 and 3 LEDs.

Ultrasonic_Rannging.ino

/*
  For use with a 4 pin Ultrasonic Distance Sensor 
  
  VCC // 5v
  GND // GND
  TRIG // Pin 13
  ECHO // Pin 12
  
  (c) Jacob Clark 2013 - http://fusionstrike.com
*/

const int trigPin = 13;
const int echoPin = 12;
const int ledPin = 11;
const int ledPin1 = 10;
const int ledPin2 = 9;

void setup() {
  
  pinMode(ledPin, OUTPUT);
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
  
  Serial.begin(9600);
}
 
void loop()
{

  long duration, inches, cm;

  pinMode(trigPin, OUTPUT);
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
 
  pinMode(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);
 
  inches = microsecondsToInches(duration);
  cm = microsecondsToCentimeters(duration);
  
  if(cm < 10 && cm < 100 && cm < 1000){
    digitalWrite(ledPin, HIGH);
    digitalWrite(ledPin1, LOW);
    digitalWrite(ledPin2, LOW);
  }
  
  if(cm > 10 && cm > 100 && cm < 1000){
   digitalWrite(ledPin, LOW);
    digitalWrite(ledPin1, HIGH);
    digitalWrite(ledPin2, LOW);
  }
  
  if(cm > 10 && cm > 100 && cm > 1000){
    digitalWrite(ledPin, LOW);
    digitalWrite(ledPin1, LOW);
    digitalWrite(ledPin2, HIGH);
  }
  
  Serial.print(inches);
  Serial.print("in, ");
  Serial.print(cm);
  Serial.print("cm");  
  Serial.println();
  
  delay(1);
}
 
long microsecondsToInches(long microseconds){
  return microseconds / 74 / 2;
}
 
long microsecondsToCentimeters(long microseconds){
  return microseconds / 29 / 2;
}