基于單片機(jī)的汽車(chē)倒車(chē)防撞系統(tǒng)的設(shè)計(jì)與制作畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告(編輯修改稿)
2024-10-06 17:41 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 BB A, 3CH MOV 30H, A SETB EX0 ； 開(kāi)外部中斷 0 POP ACC POP PSW RETI 對(duì)于一個(gè)平坦的目標(biāo)，距離測(cè)量包括兩個(gè)階段 :粗糙的測(cè)量和精細(xì)測(cè)量。 第一步：脈沖的傳送產(chǎn)生一種簡(jiǎn)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(cè)到。 第三步：檢測(cè)兩種回波的振幅與過(guò)零時(shí)間。 第四步：設(shè)置 回波放大器的所得來(lái)規(guī)格輸出，假定是 3伏。通過(guò)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(cè)量過(guò)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(guò)在低氣壓插入振幅。 第六步：通過(guò)公式計(jì)算距離 y。 四、超聲波測(cè)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，如圖 3（ a）（ b） (c) 所示。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 。 系統(tǒng)初始化后就啟動(dòng)定時(shí)器 T1 從 0開(kāi)始計(jì)數(shù)，此時(shí)主程序進(jìn)入等待，當(dāng)?shù)竭_(dá)定時(shí)時(shí)間時(shí) T1 溢出進(jìn)入 T1 中斷服務(wù)子程序；在 T1 中斷服務(wù)子程序中將啟動(dòng)一次新的超聲波發(fā)射，此時(shí)將在 引腳上開(kāi)始產(chǎn)生 40KHz 的方波，同時(shí)開(kāi)啟定時(shí)器 T0計(jì)時(shí)，為了避免直射波的繞射，需要延遲 1ms 后再開(kāi) INT0 中斷允許； INT0 中斷允許打開(kāi)后，若此時(shí)出現(xiàn)低電平則代表收到回波信號(hào)，將提出中斷請(qǐng)求進(jìn)入 INT0 中斷服務(wù)子程序，在 INT0 中斷服務(wù)子程序中將停止定時(shí)器 T0計(jì)時(shí)，讀取定時(shí)器 T0 時(shí)間值到相應(yīng)的存儲(chǔ)區(qū)，同時(shí)設(shè)置接收成功標(biāo)志；主程序一旦 檢測(cè)到接收成功標(biāo)志，將調(diào)用測(cè)溫子程序，采集超聲波測(cè)距時(shí)的環(huán)境溫度，并換算出準(zhǔn)確的聲速，存儲(chǔ)到 RAM 存儲(chǔ)單元中；單片機(jī)再調(diào)用距離計(jì)算子程序進(jìn)行計(jì)算，計(jì)算出傳感器到目標(biāo)物體之間的距離；此后主程序調(diào)用顯示子程序進(jìn)行顯示；當(dāng)一次發(fā)射、接收、顯示的過(guò)程完成后，系統(tǒng)將延遲 100ms 重新讓 T1置初值，再次啟動(dòng) T1 以溢出，進(jìn)入下一次測(cè)距。如果由于障礙物過(guò)遠(yuǎn)，超出量程，以致在 T0溢出時(shí)尚未接收到回波，則顯示 “ERROR” 重新回到主流程進(jìn)入新一輪測(cè)試。 五、結(jié)論 對(duì)所要求測(cè)量范圍 30cm~200cm 內(nèi)的平面物體做了多次測(cè)量發(fā)現(xiàn) ，其最大誤差為，且重復(fù)性好?？梢?jiàn)基于單片機(jī)設(shè)計(jì)的超聲波測(cè)距系統(tǒng)具有硬件結(jié)構(gòu)簡(jiǎn)單、工作可靠、測(cè)量誤差小等特點(diǎn)。因此，它不僅可用于移動(dòng)機(jī)器人，還可用在其它檢測(cè)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， CX20206 集成放大電路，還帶自動(dòng)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 。 附件 2：外文原文 （復(fù)印件） Ultrasonic distance meter Document Type and Number:United States Patent 5442592 Abstract:An ultrasonic distance meter cancels out the effects of temperature and humidity variations by including a measuring unit and a reference unit. In each of the units, a repetitive series of pulses is generated, each having a repetition rate directly related to the respective distance between an electroacoustic transmitter and an electroacoustic receiver. The pulse trains are provided to respective counters, and the ratio of the counter outputs is utilized to determine the distance being measured. Publication Date:08/15/1995 Primary Examiner:Lobo, Ian J. OF THE INVENTION This invention relates to apparatus for the measurement of distance and, more particularly, to such apparatus which transmits ultrasonic waves between two points. Precision machine tools must be calibrated. In the past, this has been acplished utilizing mechanical devices such as calipers, micrometers, and the like. However, the use of such devices does not readily lend itself to automation techniques. It is known that the distance between two points can be determined by measuring the propagation time of a wave travelling between those two points. One such type of wave is an ultrasonic, or acoustic, wave. When an ultrasonic wave travels between two points, the distance between the two points can be measured by multiplying the transit time of the wave by the wave velocity in the medium separating the two points. It is therefore an object of the present invention to provide apparatus utilizing ultrasonic waves to accurately measure the distance between two points. When the medium between the two points whose spacing is being measured is air, the sound velocity is dependent upon the temperature and humidity of the air. It is therefore a further object of the,present invention to provide apparatus of the type described which is independent of temperature and humidity variations. OF THE INVENTION The foregoing and additional objects are attained in accordance with the principles of this invention by providing distance measuring apparatus which includes a reference unit and a measuring unit. The reference and measuring units are the same and each includes an electroacoustic transmitter and an electroacoustic receiver. The spacing between the transmitter and the receiver of the reference unit is a fixed reference distance, whereas the spacing between the transmitter and receiver of the measuring unit is the distance to be measured. In each of the units, the transmitter and receiver are coupled by a feedback loop which causes the transmitter to generate an acoustic pulse which is received by the receiver and converted into an electrical pulse which is then fed back to the transmitter, so that a repetitive series of pulses results. The repetition rate of the pulses is inversely related to the distance between the transmitter and the receiver. In each of the units, the pulses are provided to a counter. Since the reference distance is known, the ratio of the counter outputs is utilized to determine the desired distance to be measured. Since both counts are identically influenced by temperature and humidity variations, by taking the ratio of the counts, the resultant measurement bees insensitive to such variations. DESCRIPTION of ultrasonic distance measurement 1, 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 in Figure 1, it has two piezoelectric chip and a resonance
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