Using IO port trig trigger location, to the high level signal of at least 10us module automatically sends 8 40khz fang bo, automatic detecting whether a signal return. A signal return, a high level is output through the io port echo, the time duration of the high level is ultrasonic from launch to return. The test distance = (high level time * speed of sound (340m/s)) /2ranging, the measured object area of not less than 0. 5 square meters and the plane as required to smooth, otherwise affect the measurement results.