【正文】 ent different and the nimble bination, enhances the instrument resources to be possible the reusability.(4) From definition instrument function. Traditional instrument when leaving the plant its function already determined by the manufacturer that the user cannot act according to own demand momentarily to make the revision, as soon as can only one machine use, but the hypothesized instrument may draw support from the general data acquisition installment, establishes the different software testing plan, the structure nearly random function instrument, “the software is the instrument” the thought manifests once more in here.(5) Causing between the hardware test equipment and puter39。s function and the performance realize mostly use either plete plex control, analysis or processing by the software generation of hardware technology abilities and so on hardware software, emphasized “the software is the instrument” the new concept, in the hypothesized instrument, besides the necessary hardware, has solved the present situation which the traditional instrument single instrument resources cannot share.(2) Completing the demonstration, the memory, the printing and the microprocessor control supervisor by the puter and so on, namely, regardless of any function39。s survey, control unifies in together, realizes the data analysis processing, the expression through the software. By this way constitution39。s cost and the volume greatly, and realizes through the software to the data demonstration, the memory as well as the analysis processing.The hypothesized instrument is by the puter, the application software and the instrument hardware is posed. Unifies through the application procedure the generalpurpose calculator and the functional module hardware, the user may operate this puter through the friendly graphical interface, pletes to functions and so on test data gathering, analysis, judgment, demonstration and data processing. In the hypothesized instrument system39。s automation measuring instrument system. The hypothesized instrument organically friendly blends the puter hardware source and the instrument hardware through the software into a unity, thus the puter formidable putation handling ability and the instrument hardware39。s hypothesized instrument39。s rapid development, its related hypothesized instrument technology in the data acquisition, the test automation and the instrument control domain obtains the widespread application, caused the test system and the survey control design method with realizes the technology to have the deep transformation. “the software was the instrument” already became the test and the measuring technique development important symbol. 2 Based on electronic information technology hypothesized instrument technological development and applied analysis Based on the electronic information technology39。s daybyday popularization, the accident frequency sends, the traffic congestion to intensify, the state of roads to worsen day by day, the transportation question already became the puzzle world the serious problem. From this causes traffic order worsened already serious influence modernization urban construction and national economy development. Studies vehicles39。實(shí)驗(yàn)仿真調(diào)試時(shí)，要把整個(gè)電路分成幾塊，每塊單獨(dú)調(diào)試，這樣才能減少故障率，提高調(diào)試的效率。在設(shè)計(jì)一個(gè)較大的電路系統(tǒng)時(shí)，每一個(gè)環(huán)節(jié)都是很重要的，先要有一個(gè)較為合理的原理圖，然后才能對(duì)原理圖中的每一部分進(jìn)行仿真修改，這往往不是一蹴而就的，需要不斷地反復(fù)。秒脈沖發(fā)生器以NE555芯片為核心，設(shè)計(jì)產(chǎn)生周期為1s的秒沖。狀態(tài)控制器以CD4029為核心。電路如圖66所示：
圖66 總電路總 結(jié)本系統(tǒng)由數(shù)字電路組成，整個(gè)系統(tǒng)主要由定時(shí)系統(tǒng)、狀態(tài)控制器，狀態(tài)顯示電路及秒脈沖發(fā)生器組成。圖64 秒脈沖信號(hào)發(fā)生器仿真電路示波器的輸出波形如圖65所示：圖65 示波器輸出波形圖由圖可知，該脈沖信號(hào)約為1s，符合設(shè)計(jì)要求。在仿真電路如圖 63所示：圖63 交通信號(hào)燈定時(shí)部分仿真電路
秒脈沖信號(hào)發(fā)生器的仿真電路如圖64所示。為了加快調(diào)試速度，用信號(hào)發(fā)生器產(chǎn)生的信號(hào)代替秒脈沖信號(hào)，然后在74LS245的使能控制端接3個(gè)開關(guān)，當(dāng)開關(guān)依次接低電平時(shí)，計(jì)數(shù)器應(yīng)以30送給計(jì)數(shù)器進(jìn)行倒計(jì)數(shù)。參照?qǐng)D33所示的交通信號(hào)燈狀態(tài)譯碼電路進(jìn)行仿真測(cè)試，仿真電路如圖62所示：
圖62 交通信號(hào)燈顯示電路仿真 參照?qǐng)D48所示的交通信號(hào)燈定時(shí)電路進(jìn)行仿真測(cè)試，仿真調(diào)試定時(shí)電路時(shí)，將秒信號(hào)引入定時(shí)系統(tǒng)電路的脈沖輸入端，指示燈X2作為一種狀態(tài)的指示，接在仿真測(cè)試線路上，它的作用是顯示當(dāng)某一種計(jì)數(shù)倒計(jì)時(shí)為0的時(shí)候，指示燈的連接端會(huì)輸出一個(gè)脈沖. 指示燈X2會(huì)閃亮一下。其中對(duì)于支干道的交通信號(hào)燈標(biāo)注，由于Multisim10軟件的問(wèn)題 (不支持同一字符的多次標(biāo)注)，只能標(biāo)注成小寫的rl (紅燈)、yl(黃燈)、gl (綠燈)。仿真圖采用的是和原理圖相同的引腳進(jìn)行連接的，但標(biāo)號(hào)是不一樣的。仿真電路中4029BD 的計(jì)數(shù)輸出端為 0。同時(shí)需要注意，仿真電路中的4029BD與CD4029芯片只是標(biāo)注有所不同，功能是完全相同的。交通信號(hào)燈狀態(tài)控制器仿真電路如圖61所示：圖61 狀態(tài)控制器仿真電路由于仿真軟件中秒脈沖信號(hào)發(fā)生器產(chǎn)生的仿真秒脈沖信號(hào)太慢，為了加快調(diào)試速度，在交通信號(hào)燈狀態(tài)控制器仿真電路中用信號(hào)發(fā)生器代替秒脈沖信號(hào)，信號(hào)發(fā)生器頻率設(shè)置為100Hz。由于Multisim的交互式組件、模擬驅(qū)動(dòng)儀器、實(shí)際的模擬和數(shù)字測(cè)量的整合，使Multisim在學(xué)術(shù)界、專科技術(shù)院校和大學(xué)獲得了廣泛應(yīng)用。Multisim是一個(gè)用于電路設(shè)計(jì)和仿真的EDA工具軟件，由于其強(qiáng)大的功能，形象生動(dòng)的仿真效果，友好的界面，豐富的元件庫(kù)和儀表庫(kù)，在我國(guó)各級(jí)各類學(xué)校得到廣泛的推廣應(yīng)用，尤其是電類專業(yè)可以將其作為電子電路的教學(xué)示教、仿真實(shí)驗(yàn)、電子電路的設(shè)計(jì)等。Multisim幫助工程師優(yōu)化電路設(shè)計(jì)，減少錯(cuò)誤和原型重復(fù)。憑借Multisim，可以立即創(chuàng)建具有完整組件庫(kù)的電路圖，并利用工業(yè)標(biāo)準(zhǔn)SPICE模擬器模仿電路行為[9]。通過(guò)Multisim和虛擬儀器技術(shù)，PCB設(shè)計(jì)工程師和電子學(xué)教育工作者可以完成從理論到原理圖捕獲與仿真再到原型設(shè)計(jì)和測(cè)試這樣一個(gè)完整的綜合設(shè)計(jì)流程。 工程師們可以使用Multisim交互式地搭建電路原理圖，并對(duì)電路行為進(jìn)行仿真。若設(shè)占空比=%50，又知交通信號(hào)燈的振蕩周期是1s，可得到本次所需要的元器件阻值：.R1≈39KΩR2≈51KΩC≈10uFC0≈10nF第六章 仿真軟件介紹及仿真分析 仿真軟件介紹Multisim是加拿大圖像交互技術(shù)公司（Interactive Image Technoligics簡(jiǎn)稱IIT公司)推出的以Windows為基礎(chǔ)的仿真工具，適用于初級(jí)的模擬/數(shù)字電路板的設(shè)計(jì)工作。如此重復(fù)上述過(guò)程，U0為連續(xù)的矩形波。當(dāng)Uc下降略低于1/3VCC時(shí)，比較器C2的輸出為“0”，將觸發(fā)器置“1”， U0又由“0”變?yōu)椤?”。圖53 秒脈沖電路圖圖54 波形圖接通電后，它經(jīng)過(guò)電阻R1和R2對(duì)電容C充電，當(dāng)UC上升略高于2/3VCC時(shí)，比較器C1的輸出為“0”，將觸發(fā)器置“0”，U0為“0”。只需在+VCC端接上+3V的電源，就能在3腳產(chǎn)生周期性的方波。它沒(méi)有穩(wěn)定狀態(tài)，同時(shí)毋須外加發(fā)脈沖，就能輸出一定頻率的矩形脈沖[8]（自激振蕩）。表51為555的功能表，它全面表示了555的基本功能。當(dāng)2端的輸入高電壓高于VCC/3時(shí)，C2輸出為1；當(dāng)輸入電壓低于VCC/3時(shí)，C2的輸出為0，使基本觸發(fā)器置1；3端OUT為輸出端；4端RT是復(fù)位端，當(dāng)=0時(shí)，基本觸發(fā)器直接置0，使Q=0，=1；5端為電壓控制端，如果C0 端另加控制電壓，則可以改變C1，C2的參考電壓。VCC = 5 V, RL = ∞ =6mA ，可直接推動(dòng)多種自動(dòng)控制的負(fù)載。其延時(shí)范圍極廣，可由幾微秒至幾小時(shí)之久。NE555是屬于555系列的計(jì)時(shí)IC的其中的一種型號(hào)，555系列IC的接腳功能及運(yùn)用都是相容的，只是型號(hào)不同的因其價(jià)格不同其穩(wěn)定度、省電、可產(chǎn)生的振蕩頻率也不大相同。脈沖寬度和位置的調(diào)至電路以及報(bào)警器，應(yīng)用極其廣泛。還可以在儀器儀表、自動(dòng)化裝置和各種電器中作定時(shí)和時(shí)間延遲等控制。在應(yīng)用中都是一樣的效果。在波形的產(chǎn)生與變換、測(cè)量與控制、家用電器、電子玩具等許多領(lǐng)域中都得到了應(yīng)用。 555 定時(shí)器介紹555 定時(shí)器是一種模擬和數(shù)字電路混合的中規(guī)模集成電路。由于74LS245選通信號(hào)要求低電平有效，故Q1經(jīng)過(guò)一個(gè)非門輸出后接相應(yīng)74LS245的選通控制端。圖46 電路結(jié)構(gòu) 圖47 圖形符號(hào)SR鎖存器的特性表如表42所示：表42 SR鎖存器特性表SR鎖存器在電路中的作用是保證數(shù)碼管顯示數(shù)字的時(shí)間間隔為1s。圖45 74LS245的引腳圖根據(jù)邏輯功能的不同分為： RS觸發(fā)器、 JK觸發(fā)器、 T觸發(fā)器、 D觸發(fā)器。其中芯片引腳為芯片使能端(有的標(biāo)為)，為低電平時(shí)，緩沖器才能工作。表41 七段