设计一个测距器，可以应用于汽车倒车、建筑施工工地以及一些工业现场的位置监控，也可用于如液位、井深、管道长度的测量等场合。-The design of a range-finder, can be applied to vehicles reversing, construction site, as well as the location of some industrial-site monitoring, can also be used such as liquid level, dep