【正文】 tant, leads to a of this study is based on single chip ultrasonic ranging system is a kind of can advance to the driver issued audiovisual speech signal detection is installed in cars that can detect trying to approach the body of a car pedestrians and vehicles or around obstacles, Can send to the driver and crew imminent danger ahead of the signal, prompting a crash drivers take emergency measures to cope with special danger, avoid the question design significanceAlong with the development of modern society industrialization process, car this traffic tools are used for more and more people, but any problem has obvious that along with the increase in vehicles, traffic accident, which led to the frequent occurrence of casualties and property losses number highway traffic accident analysis showed that more than 80% of the accident due to the driver reaction inferior things, caused more than 65% of vehicle collision, the rest belongs to tracing cauda collided belongs to the side Automobile Company for all kinds of traffic accident research shows that: if the driver can early 1S are aware中原工學院畢業(yè)設計（論文）譯文that a accident risk and take the appropriate corrective measures, the overwhelming majority of traffic accidents can be , vigorously research and development as the automotive anticollision device etc active car auxiliary safe device, reduce the burden and misjudgments drivers to improve the traffic safety will play an important , this kind of product research and development has great realize meaning and broad application Ultrasonic ranging in automotive applications introducedUltrasonic backdraft rangefinder(known as electron optics)automotive anticollision reversing device, can safe adjunct to sound or more intuitive digital form the dynamic display of around earlier products is to use buzzer alarm, hum more anxious, and says vehicles from obstructions product can display the car from the body after the obstacles of its products detection range in ~ m, some product can achieve ~ m, and have distance display, sound alarm, areawarning and azimuth instructions, some products also has the boot selfchecking appeared on the market at present with voice alarm function of products are the main problem is big, alarm measuring blind area lags behind, without considering the automobile braking inertial factors and make drivers brake lag, the antiinterference ability is not strong, misstatement or automotive anticollision radar is able to realize impactproof alarm functions, basically have ultrasonic this intangible ruler, it recently obstacles distance measurement, and told to the ultrasonic rangefinding principle simple: it emit ultrasonic echo, and receive reflected by microcontroller counter obtain both lag using formula S = t, Ct / 2 calculating distances, including S for cars and obstacles, C for the distance between the sound wave propagation in the medium paper introduces the ultrasonic ranging system only have 2 ultrasonic transducer(known as probe)respectively, decorate in cars left and right after after 2 of detecting forward and reverse direction obstacle distance, the rearview mirror builtin display element display distance and direction, issued must be sound, plays the role of hints and USES a STC89C52 SCM two way ultrasonic signal cyclicly refers to the 20HHZ wave frequency is order to use the ultrasonic detection means, must generate as ultrasonic wave and receiving the functions of the device is called the中原工學院畢業(yè)設計（論文）譯文ultrasonic sensor, habit, ultrasonic transducer or ultrasonic sensors have both transmitters and receivers, but a ultrasonic sensors can also has the sending and receiving the sound waves of the dual sensors is using the principle of piezoelectric effect and ultrasonic energy conversion, be in namely emit ultrasonic, energy conversion, launch ultrasonic, And in the stockades, received echo ultrasonic vibration into electrical ranging principle generally USES the time method for the measured ultrasonic from the launch to meet obstacles returns experience of time, again multiply ultrasonic speed of get twice the distance between the sound source and distance a variety of ways, short can use ruler, longrange laser displacement etc, are suitable for high accuracy of ultrasonic ranging in long distance of ultrasound in standard air of propagation speed meters per second, by singlechip microputer is responsible for timing, SCM use M crystals, so the system of measurement precision theory can achieve mm of ultrasonic directivity strong, energy consumption is slow, in a medium transmission distance, thus ultrasonic can be used for distance ultrasonic detection distance, the design is more convenient, puting procese also relatively simple, and the measurement precision can also meet the generator can be divided into two kinds: one kind is to use electrical means producing ultrasonic, one kind is with mechanical approach to producing design belongs to nearly distance measurement, can use monly used the piezoelectric ultrasonic transducer to achieve trigger ultrasonic ranging work, can according to measuring launch reflection wave wave and the time interval between the measured distance, so as to achieve the mainly have three ranging methods:(1)phase assay, phase assays high precision, but detection though limited range，(2)sound amplitude assay, acoustic amplitude assay vulnerable reflection wave influence。思考：至于為什么不用接收管做放大電路，因為放大倍數(shù)搞不好，集成放大電路，還帶自動電平增益控制，放大倍數(shù)為76db，中心頻率是38k到40k，剛好是超聲波傳感器的諧振頻率。定時中斷服務子程序完成三方向超聲波的輪流發(fā)射，外部中斷服務子程序主要完成時間值的讀取、距離計算、結果的輸出等工作。如果逆向發(fā)生在回波中，決定要不通過在低氣壓插入振幅。通過脈沖的周期設置下一個脈沖。POP ACCPOP PSWRETI 對于一個平坦的目標，測量距離包括兩個階段：粗糙的測量和精細的測量。關外部中斷0 讀取時間值MOV R7,TH0。轉至右側距電路中斷服務程序jnb ,left。IC2是帶有鎖定環(huán)的音頻譯碼集成塊LM567，內部壓控振蕩器的中心頻率f0=1/，電容C4決定其帶寬。圖1 電路原理圖中原工學院畢業(yè)設計（論文）譯文 40kHz脈沖的產生與超聲波發(fā)射測距系統(tǒng)中的超聲波傳感器采用UCM40的壓電陶瓷，它的工作電壓是40kHz的脈沖信號，這由單片機執(zhí)行下面的程序來產生。強度較強的脈沖會比強度較弱的脈沖超過界限的時間早點，因此我們會認為強度較強的脈沖屬于較近的物體。這個信號恰恰選于噪音水平之上，然而脈沖到達時間被定義為