【正文】 With the development of society and economy of transportation industry is booming, the number of cars in the sharp rise. Traffic congestion has bee more and more serious, the crash occurred repeatedly, resulting from the inevitable casualty and economic loss, in view of this situation, design a kind of fast response, high reliability and more economy car collision avoidance warning system to be imperative, ultrasonic ranging method is the most mon type of distance measuring method, this paper describes the use of ultrasonic locating design a backdraft anticollision alarm system. The content of the thesis is based on the AT89C51 singlechip integration, design based on AT89C51 backdraft anticollision alarm system. The system uses a bination of hardware and software, the method of module, and multiuse characteristics. This paper summarizes the development and basic principle of ultrasonic detection, introduces the principle and characteristics of ultrasonic sensor. Some of the main parameters for the system were discussed, and introducing ultrasonic ranging system functions basis, the overall position of the system, through a variety of transmitting and receiving circuit design parison, the best design scheme, and various system design unit this paper introduces the principle of. On the position of the system circuit chip are introduced, and elaborated the principles of their work. This paper introduces the software structure of system, programmed to realize the function of the system. Finally, through the analysis of system error, an improved scheme is presented. Key words: single chip ultrasonic AT89C51 重慶科技學院高等教育自學考試本科畢業(yè)論文 畢業(yè)設計（論文） 目 錄 1 超聲檢測發(fā)展綜述 ........................................................................................................................ 1 2 超聲波介紹 ................................................................................................................................. 2 超聲波傳感器及其測距原理 ........................................................................................... 2 什么是超聲波 ................................................................................................................... 2 壓電式超聲波傳感器簡介 ............................................................................................... 2 頻率特性 ........................................................................................................................... 4 指向特性 ........................................................................................................................... 5 3 單片機倒車防撞報警系統(tǒng)各組成單元方案設計 ..................................................................... 6 發(fā)射接收電路方案 設計 ................................................................................................... 6 系統(tǒng)顯示電路設計 ........................................................................................................... 7 系統(tǒng)報警電路設計 ........................................................................................................... 7 單片機復位電路 ............................................................................................................... 8 時鐘電路 ........................................................................................................................... 9 穩(wěn)壓電源 ........................................................................................................................... 9 4 系統(tǒng)硬件及軟件實現(xiàn) ................................................................................................................. 10 單片機的選擇 ................................................................................................................. 10 AT89C51的主要性能參數(shù) .............................................................................................. 10 AT89C51的結構 .............................................................................................................. 10 CX20226芯片介紹 .......................................................................................................... 11 系統(tǒng)軟件結構 ................................................................................................................. 12 硬件連接方法 ................................................................................................................. 12 .............................................................................................................. 12 超聲波接收及顯示程序 ................................................................................................. 13 1602顯示初始化寫指令寫數(shù)據程序 ............................................................................ 14 蜂鳴報警程序 ............................................................................................................... 18 結束語 ............................................................................................................................................ 19 謝詞 ................................................................................................................................................ 20 參考文獻