设计实现了一种倒车用超声波测距仪;系统以MC68HC908GP32型微控制器为核心进行模块化设计,采用4路探头进行超声波的发射和接收,通过通道选择电路对四路回波进行循环检测;回波信号经多重反馈带通滤波放大电路和过零比较电路后,触发定时器的输入捕捉中断,微控制器存储回波往返时间,经过温度校正和运算后送所测最短距离进行显示并报警;经调试该仪器能满足1.5m范围内的距离测距要求,测量“盲区”小于20cm,具有高的精确度和可靠性;适当改进后可用于其它短距离测距要求的相关系统中。An ultrasonic distance measurement system for backing a car is designed.It is mainly designed with the adoption of the MCU MC68HC908GP32 together with other circuit module.The system detects circularly the four channels which is composed of four probes of transmitting and receiving the ultrasonic wave through select circuit.The reflected signal is disposed by the magnified circuit of multiple feedback band-pass filter and zero-crossing comparative circuit.When the MCU detects the reflecting wave,interrupting of timer would be triggered,and the trip-back time is saved in memory cell.The shortest distance operated through temperature correction is displayed and the system will alarm when the distance is less than the fixed parameters.After debugged,system can meet actual demand within 1.5 meter.The blind distance is less than 20cm and the system is of high precision and reliability.It can also be applied to other relative systems after properly improved
