SainSmart Ultrasonic Module HC-SR04 Distance Sensor for Arduino UNO MEGA R3 Mega2560 Duemilanove Nano Robot XBee ZigBee

There are 4 pins out of the module: VCC , Trig, Echo, GND . So it's a very easy interface for controller to use it ranging. The all process is : pull the Trig pin to high level for more than 10us impulse , the module start ranging ; finish ranging , If you find an object in front , Echo pin will be high level , and based on the different distance