SainSmart Ultrasonic Module HC-SR04 Distance Sensor for Arduino UNO MEGA R3 Mega2560 Duemilanove Nano Robot XBee ZigBee Using IO trigger for at least 10us high level signal The Module automatically sends eight 40 kHz and detect whether there is a pulse signal back IF the signal back, through high level , time of high output IO duration is the time from sending ultrasonic to returning. Test distance = (high level timevelocity of sound (340M/S) /2 Power supply :5V DC, quiescent current : &lt;2mA, effectual angle: &lt;15ranging distance : 2cm~500 cmresolution : 0.3 cm