CJRSLRB 5 Pcs 5 Pack Ultrasonic Module HC-SR04 Distance Measuring Transducer Sensor for Arduino UNO MEGA R3 Mega2560 Duemilanove Nano Robot Power supply :5V DC, quiescent current : &lt;2mA,effectualangle: &lt;15 ranging distance : 2cm~500 cm resolution : 0.3 cm Using IO trigger for at least 10us high level signal. There are 4 pins out of the module: VCC , Trig, Echo, GND. The Module automatically sends eight 40 kHz and detect whether there is a pulse signal back. Distance = ((Duration of high level)*(Sonic :340m/s))/2