【正文】 詞：超聲波定位；停車倒車；AT89S51AbstractWith the social and economic development and transportation continues to boom, the automobile quantity climbs in the first mate. Traffic congestion condition also day by day serous, the collision event occurred repeatedly, has caused the inevitable person casualties and the economic loss, in view of this kind of situation, designed one kind to respond quickly, the reliability was high also a more economical automobile guards against hits the early warning system imperative, the ultrasonic wave range finding was the most mon one distance range finder method, this article introduces is guards against using the ultrasonic wave range finding design one kind of reversing collision avoidance system.The paper is based on the ultrasonic distance reversing collision avoidance system design, mainly using ultrasound features and advantages, ultrasound ranging system and the integration with the integration AT89S51 monolithic integrated circuit, AT89S51 monolithic integrated circuit based on the design of a reverse collision avoidance warning systems. The system used software and hardware integrated approach of modular and multiuse characteristics.The paper outlines the development and the basic principles of ultrasound tests on the principles and characteristics of ultrasound sensors. Some of the main parameters for the system were discussed, and introducing ultrasonic ranging system functions basic, the overall position of the system. Through multiple launch reception circuit design parison, the best designed programme drawn, and various system design modules principles introduced. On the position of the system circuit chip introduced and elaborated the principles of their work. Papers introduced system software architecture, through programming to achieve system function.Key words: Ultrasonic Positioning。超聲波測距是利用其反射特性，當(dāng)車輛后退時(shí)，超聲波測距傳感器利用超聲波檢測車輛后方的障礙物位置，并利用LED顯示出來，當(dāng)?shù)竭_(dá)一定距離時(shí)，系統(tǒng)能發(fā)出報(bào)警聲，進(jìn)而提醒駕駛?cè)藛T，起到安全的左右。隨著科學(xué)技術(shù)的快速發(fā)展，超聲波的應(yīng)用將越來越廣泛。對設(shè)計(jì)的電路進(jìn)行分析能夠產(chǎn)生超聲波，實(shí)現(xiàn)超聲波的發(fā)送和接收，從而實(shí)現(xiàn)利用超聲波測距的方法測量物體之間的距離。目前在近距離測量方面常用的是壓電式超聲波換能器。 超聲測距原理 超聲波概述超聲波是一種頻率超過20的機(jī)械波。目前常用的超聲波傳感器有兩大類，即電聲型與流體動力型。其具有下列的特性：把這種材料置于電場之中，它就產(chǎn)生一定的應(yīng)變；相反，對這種材料施以外力，則由于產(chǎn)生了應(yīng)變就會在其內(nèi)部產(chǎn)生一定方向的電場。這種超聲傳感器需要的壓電材料較少，價(jià)格低廉，且非常適用于氣體和液體介質(zhì)中。發(fā)射超聲波時(shí)，加在其上面的交變電壓的頻率要與它的固有諧振頻率一致。假設(shè)超聲波在空氣中的傳播速度為，根據(jù)計(jì)時(shí)器記錄的時(shí)間，發(fā)射點(diǎn)距障礙物的距離， Fig. Ultrasonic ranging principle，兩探頭中心距離的一半用M表示，超聲波單程所走過的距離用表示，由圖可得： (1) (2)將式(2)帶入式(1)得： (3)在整個(gè)傳播過程中，超聲波所走過的距離為： (4)式中：為超聲波的傳播速度，為傳播時(shí)間，即為超聲波從發(fā)射到接收的時(shí)間。接收電路使用三極管組成的放大電路，該電路簡單，調(diào)試工作小較小。4k字節(jié)在系統(tǒng)編程（ISP）Flash閃速存儲器6個(gè)中斷源空閑方式停止CPU的工作，但允許RAM，定時(shí)／計(jì)數(shù)器，串行通信口及中斷系統(tǒng)繼續(xù)工作。單片機(jī)控制著超聲波的發(fā)送，超聲波發(fā)送完畢后，立即啟動內(nèi)部計(jì)時(shí)器T0計(jì)時(shí)，立即停止內(nèi)部計(jì)時(shí)器計(jì)時(shí)。，經(jīng)BG1推動超聲波脈沖變壓器，在脈沖變壓器次級形成60VPP的電壓，加載到超聲波發(fā)送頭上，驅(qū)動超聲波發(fā)射頭發(fā)射超聲波。s，所以只能產(chǎn)生半周期為12181。這里使用的是I N 4148檢波二極管，輸出的直流信號即兩二極管之間電容電壓。方式二：，提供聲響報(bào)警信號，電路由電阻R三極管BG蜂鳴器BY組成，當(dāng)測量值低于事先設(shè)定的報(bào)警值時(shí)，蜂鳴器發(fā)出“滴、滴、滴…..”報(bào)警聲響信號，測量值高于設(shè)定的報(bào)警值時(shí)，停止發(fā)出報(bào)警聲響。測距間隔中，整個(gè)程序主要進(jìn)行循環(huán)顯示測量結(jié)果。 csbfs()。 s=TH1。超聲波發(fā)射的完整波形個(gè)數(shù)：共計(jì)四個(gè) here: cpl 。其中溫度對超聲波在空氣中的傳播速度有明顯的影響，當(dāng)需要精確確定超聲波傳播速度時(shí)，必須考慮溫度的影響。③收到中斷到中斷響應(yīng)停止計(jì)時(shí)之間的滯后。同時(shí)選用質(zhì)量好的晶振。所以，為了提高壓電轉(zhuǎn)換效率，提高超聲測距精度和范圍，應(yīng)盡量提高超聲傳感器外加脈沖電壓的幅值。超聲波測距儀還可以做如下改進(jìn)：系統(tǒng)的動態(tài)性能不高，被測物體表面移動速度很小時(shí)，可以實(shí)現(xiàn)跟蹤測量；移動速度過大，波動較大時(shí)，誤差變大。為了抑制外部干擾，接收裝置可以采用過零檢測裝置，保證接收到得超聲波為物體反射回來的超聲波，從而有效地抑制超聲波發(fā)射電路的輻射干擾。附錄一 超聲波測距原理圖 23