【正文】 障礙物的距離(s)，即：s=340t/2超聲波測距系統(tǒng)的電路設(shè)計(jì)系統(tǒng)的特點(diǎn)是利用單片機(jī)控制超聲波的發(fā)射和對超聲波自發(fā)射至接收往返時(shí)間的計(jì)時(shí)，單片機(jī)選用C51，經(jīng)濟(jì)易用，且片內(nèi)有4K的ROM，便于編程。電路原理圖如圖1所示。圖1 電路原理圖 40kHz 脈沖的產(chǎn)生與超聲波發(fā)射測距系統(tǒng)中的超聲波傳感器采用UCM40的壓電陶瓷傳感器，它的工作電壓是40kHz的脈沖信號，這由單片機(jī)執(zhí)行下面程序來產(chǎn)生。puzel： mov 14h, 12h；超聲波發(fā)射持續(xù)200mshere： cpl ； 輸出40kHz方波 nop ； nop ； nop ； djnz 14h，here； ret，單片機(jī)執(zhí)行上面的程序后， 端口輸出一個(gè)40kHz的脈沖信號，經(jīng)過三極管T放大，驅(qū)動超聲波發(fā)射頭UCM40T，發(fā)出40kHz的脈沖超聲波，且持續(xù)發(fā)射200ms。右側(cè)和左側(cè)測 ，工作原理與前方測距電路相同。接收頭采用與發(fā)射頭配對的UCM40R，將超聲波調(diào)制脈沖變?yōu)榻蛔冸妷盒盘?，?jīng)運(yùn)算放大器IC1A和IC1B兩極放大后加至IC2。IC2是帶有鎖 定環(huán)的音頻譯碼集成塊LM567，內(nèi)部的壓控振蕩器的中心頻率f0=1/，電容C4決定其鎖定帶寬。調(diào)節(jié)R8在發(fā)射的載頻上，則LM567 輸入信號大于25mV，輸出端8腳由高電平躍變?yōu)榈碗娖?，作為中斷請求信號，送至單片機(jī)處理.前方測距電路的輸出端接單片機(jī)INT0端口，中斷優(yōu)先級最高，左、右測距電路的輸出通過與門IC3A的輸出接單片機(jī)INT1端口，中斷源的識別由程序查詢來處理，中斷優(yōu)先級為先右后左。部分源程序如下：receive1：push psw push acc clr ex1； 關(guān)外部中斷1 jnb ,right；,轉(zhuǎn)至右測距電路中斷服務(wù)程序 jnb ,left；,轉(zhuǎn)至左測距電路中斷服務(wù)程序return： SETB EX1； 開外部中斷1 pop acc pop psw retiright： ... ； 右測距電路中斷服務(wù)程序入口 ajmp returnleft： ... ； 左測距電路中斷服務(wù)程序入口 ajmp return在啟動發(fā)射電路的同時(shí)啟動單片機(jī)內(nèi)部的定時(shí)器T0，利用定時(shí)器的計(jì)數(shù)功能記錄超聲波發(fā)射的時(shí)間和收到反射波的時(shí)間。當(dāng)收到超聲波反射波時(shí)，接收電路 輸出端產(chǎn)生一個(gè)負(fù)跳變，在INT0或INT1端產(chǎn)生一個(gè)中斷請求信號，單片機(jī)響應(yīng)外部中斷請求，執(zhí)行外部中斷服務(wù)子程序，讀取時(shí)間差，計(jì)算距離。其部分源程序如下：RECEIVE0： PUSH PSW PUSH ACC CLR EX0 ； 關(guān)外部中斷0 MOV R7, TH0 ； 讀取時(shí)間值 MOV R6, TL0 CLR C MOV A, R6 SUBB A, 0BBH； 計(jì)算時(shí)間差 MOV 31H, A ； 存儲結(jié)果 MOV A, R7 SUBB A, 3CH MOV 30H, A SETB EX0 ； 開外部中斷0 POP ACC POP PSW RETI對于一個(gè)平坦的目標(biāo)，距離測量包括兩個(gè)階段:粗糙的測量和精細(xì)測量。第一步：脈沖的傳送產(chǎn)生一種簡單的超聲波。第二步：根據(jù)公式改變回波放大器的獲得量直到回?fù)鼙粰z測到。第三步：檢測兩種回波的振幅與過零時(shí)間。第四步：設(shè)置回波放大器的所得來規(guī)格輸出，假定是3伏。通過脈沖的周期設(shè)置下一個(gè)脈沖。根據(jù)第二部的數(shù)據(jù)設(shè)定時(shí)間窗。第五步：發(fā)射兩串脈沖產(chǎn)生干擾波。測量過零時(shí)間與回波的振幅。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。第六步：通過公式計(jì)算距離y。超聲波測距系統(tǒng)的軟件設(shè)計(jì)軟件分為兩部分，主程序和中斷服務(wù)程序。主程序完成初始化工作、各路超聲波發(fā)射和接收順序的控制。定時(shí)中斷服務(wù)子程序完成三方向超聲波的輪流發(fā)射，外部中斷服務(wù)子程序主要完成時(shí)間值的讀取、距離計(jì)算、結(jié)果的輸出等工作。結(jié)論對所要求測量范圍30cm~200cm內(nèi)的平面物體做了多次測量發(fā)現(xiàn)，且重復(fù)性好。可見基于單片機(jī)設(shè)計(jì)的超聲波測距系統(tǒng)具有硬件結(jié)構(gòu)簡單、工作可靠、測量誤差小等特點(diǎn)。因此，它不僅可用于移動機(jī)器人，還可用在其它檢測系統(tǒng)中。思考：至于為什么接收不用晶體管做放大電路呢，因?yàn)榉糯蟊稊?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 。外文原文Ultrasonic ranging system designPublication title: Sensor Review. Bradford: 1993. Vol. 13ABSTRACTUltrasonic ranging technology has wide using worth in many fields，such as the industrial locale，vehicle navigation and sonar engineering．Now it has been used in level measurement，selfguided autonomous vehicles, fieldwork robots automotive navigation，air and underwater target detection，identification，location and so on．So there is an important practicing meaning to learn the ranging theory and ways deeply. To improve the precision of the ultrasonic ranging system in hand，satisfy the request of the engineering personnel for the ranging precision，the bound and the usage，a portable ultrasonic ranging system based on the single chip processor was developed．Keywords：Ultrasound r，Ranging System，Single Chip ProcessorWith the development of science and technology, the improvement of people39。s standard of living, speeding up the development and construction of the city. urban drainage system have greatly developed their situation is constantly improving. However, due to historical reasons many unpredictable factors in the synthesis of her time, the city drainage system. In particular drainage system often lags behind urban construction. Therefore, there are often good building excavation has been building facilities to upgrade the drainage system phenomenon. It brought to the city sewage, and it is clear to the city sewage and drainage culvert in the sewage treatment system. fort is very important to people39。s lives. Mobile robots designed to clear the drainage culvert and the automatic control system Free sewage culvert clear guarantee robot, the robot is designed to clear the culvert sewage to the core. Control System is the core ponent of the development of ultrasonic range finder. Therefore, it is very important to design a good ultrasonic range finder.2. A principle of ultrasonic distance measurement The principle of piezoelectric ultrasonic generator Piezoelectric ultrasonic generator is the use of piezoelectric crystal resonators to work. Ultrasonic generator, the internal structure as shown, it has two piezoelectric chip and a resonance plate. When it39。s two plus pulse signal, the frequency equal to the intrinsic piezoelectric oscillation frequency chip, the chip will happen piezoelectric resonance, and promote the development of plate vibration resonance, ultrasound is generated. Conversely, if the two are not interelectrode voltage, when the board received ultrasonic resonance, it will be for vibration suppression of piezoelectric chip, the mechanical energy is converted to electrical signals, then it bees the ultrasonic receiver. The traditional way to determine the moment of the echo39。s arrival is based on thresholding the received signal with a fixed reference. The threshold is chosen well above the noise level, whereas the moment of arrival of an echo is defined as the first moment the echo signal surpasses that threshold. The intensity of an echo reflecting from an object strongly depends on the object39。s nature, size and distance from the sensor. Further, the time interval from the echo39。s starting point to the moment when it surpasses the threshold changes with the intensity of the echo. As a consequence, a considerable error may occur Even two echoes with different intensities arriving exactly at the same time will surpass the threshold at different mome