用51单片机做的4路超声波倒车雷达，显示为三位数码管，显示范围为3.15米-0.25显示精度0.05米--To do with 51 single-chip 4-way ultrasonic reversing radar, shown as three digital tube, showing the range of 3.15 meters-0.25 show the accuracy of 0.05 meters