汽车倒车防撞报警系统

摘要
本文介绍了AT89C2051单片机的性能和特点。介绍了超声波的原理及其主要用途，在分析了超声波测距原理的基础上，指出了设计测距仪的思路和所需考虑的问题。给出了实现超声波测距方案的软、硬件设计系统框图，以及相应的报警显示装置。并比较了超声波测距与其它测距方法的优缺点，比如红外线测距等方法。该设计系统经校正后，其测量精度可达5cm，探测角度为40度左右，效果比较理想。目前超声波测距主要应用于倒车雷达、建筑施工工地以及一些工业现场。例如：液位、井深、管道长度等场合。目前国内一般使用专用集成电路设计超声波测距仪，但是专用集成电路虽然集成度很高，便于批量生产，但它的成本很高,并且没有显示，操作使用很不方便。本文介绍的一种以AT89C2051单片机为控制核心的低成本、高精度、微型化数字显示超声波测距仪的硬件电路和软件设计方法，设计需要的材料常见便于制作，需要的主要元件有：AT89C2051单片机、7404非门、超声波探头一对（收发各一个）、液晶显示器（或者数码管）一个、放大器一个本设计使用LM324四输入运放、12M晶振一个，以及一些小电阻电容。该产品已经做出，经实验该仪器工作稳定，性能良好，可靠性高。该装置采用软、硬件校正，提高了测量精度和整机的可靠性。该装置极大的提高了泊车时的安全性，做到了倒车时对突然闯入汽车尾部的人或障碍物的探测报警，增强了驾驶员对倒车安全的操控性。
关键词:超声波；换能器；测距； AT89C2051

Development of Ultrasonic Range Finder for Parking
Abstract:
This application report describes a distance-measuring system based on ultrasonic sound utilizing the AT89C2051ultralow-power micro-controller.Thesystem transmits a burst of ultrasonic sound waves towards the subject and then receives the corresponding echo. The at89c2051 integrated analog comparator Comparator A is used to detect the arrival of the echo to the system.  The time taken for the ultrasonic burst to travel the distance from the system to the subject and back to the system is accurately measured by the at89c2051. Assuming the speed of sound in air at room temperature to be 1100 ft/s, the MSP430 computes the distance between the system and the subject and displays it using a two-digit static LCD driven by its integrated LCD driver. The distance is displayed in inches with an accuracy of 1 inch. The minimum distance that this system can measure is eight inches and is limited by the transmitter’s transducer settling-time. The maximum distance that can be measured is ninety-nine inches. The amplitude of the echo depends on the reflecting material, shape, and size. Sound-absorbing targets such as carpets and reflecting surfaces less than two square feet in area reflect poorly. The maximum measurable range is lower for such subjects. If the amplitude of the echo received by the system is so low that it is not detectable by the Comparator _A, the system goes out of range. This is indicated by displaying the error message E This paper describes the basic principle of the ultrasonic range finder for parking which is developed by adopting microprocessor technology. Mathematics model of measurement and calculation as well as realization methods is also discussed. Software calibration method is used to increase measuring accuracy and reliability. Actual application shows that the security is greatly insured when parking.
Keywords: Ultrasonic； Range-finding； MicroprocessorAT89C2051

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