This program help you know the distance between the HC-SR04 module and a object. Using the serial monitor of Arduino IDE. Take care because each HC-SR04 has his own calibration
It is little simplification of Ultrasonic.cpp - Library for HC-SR04 Ultrasonic Ranging Module. Library Created by ITead studio. Apr 20, 2010. iteadstudio.com Modificated by Xarpe Serpe