Accurate distance measurement by an autonomous ultrasonic system combining time-of-flight and phase-shift methods

Ultrasonic sensor distance measurements are based on the evaluation of the time-of-flight or on the determination of the phase difference between a transmitted and a received signal. Digital signal processing methods are developed in order to extract the useful information from the samples acquired from the received wave. This paper presents an efficient algorithm for distance measurement combining both the propagation time method and the phase difference method and relying on a low rate sampling technique allowed by the limited bandwidth of the ultrasonic transducers. The measuring system was implemented and tested on a compact Motorola MC68HC16 based platform, with a minimum of attached hardware. Experimental results show an accuracy better than 1 mm.