【正文】 P2口第一功能是當(dāng)不帶片外存儲(chǔ)器時(shí)，作為通用 I/O 口； P2口第二功能是當(dāng)帶片外存儲(chǔ)器時(shí)，與 P0 口配合 ，傳送片外存儲(chǔ)器的高 8 位地址，共同選中片外存儲(chǔ)器單元。當(dāng) EA 端保持高電平時(shí)，單片機(jī)復(fù)位后訪問片內(nèi)存儲(chǔ)器 ROM。這種傳感器不怕灰塵、油污，在工業(yè)現(xiàn)場應(yīng)用廣泛。內(nèi)含兩個(gè) H 橋的高電壓大青海大學(xué)本科生畢業(yè)設(shè)計(jì)： 基于單片機(jī)控制直流電機(jī)調(diào)速控制系統(tǒng)設(shè)計(jì) 14 化工 學(xué)院 電流全橋式驅(qū)動(dòng)器，可以用來驅(qū)動(dòng)直流電動(dòng)機(jī)和步進(jìn)電動(dòng)機(jī)、繼電器、線圈等感性負(fù)載；采用標(biāo)準(zhǔn)TTL 邏輯電平信號(hào)控制；具有兩個(gè)使能控制端口，分別控制兩個(gè)電機(jī)的啟動(dòng)和制動(dòng)；有一個(gè)邏輯電源輸入端，使內(nèi)部邏輯電路部分在低 電壓下工作；它可以外接電阻，把變化量反饋給控制電路。同理。為了避免 CPU 多次處理按鍵的一次閉合，應(yīng)采用措施消除抖動(dòng)。獨(dú)立鍵盤如圖 25 所示。 綜合考慮選方案二，采用定頻調(diào)寬法。對(duì)于直流電機(jī) 來說人為機(jī)械特性方程式為： nnTCC RCUn TE aE a ????? 02?? （ 21） 式中： 0n 是電動(dòng)機(jī)的理想空載轉(zhuǎn)速，其值為?EaCUn ?0； n? 是轉(zhuǎn)速差； aU 是電樞供電電壓（ V）；aR 是電樞回路總電阻（ Ω）； ? 是勵(lì)磁磁通（ Wb）； EC 是電勢(shì)系數(shù)； TC 轉(zhuǎn)矩系數(shù)[7]。所以，此處的電路在速度的顯示上失去了其真實(shí)性。 控制模塊：主要由 AT89S51 單片機(jī)的外部擴(kuò)展電路組成。 小結(jié) 首先 主要分析了 直流電機(jī)調(diào)速系統(tǒng)研究的背景和研究的目的及意義；并且介紹了直流電機(jī)控制的國內(nèi)外研究現(xiàn)狀及發(fā)展情況； PWM 變頻調(diào)速的發(fā)展前景；研究方法；以及課題主要研究內(nèi)容及預(yù)期目標(biāo)做了簡要說明。 現(xiàn)代的變頻器采用了通信技術(shù)領(lǐng)域中的脈寬調(diào)制技術(shù)，具體一點(diǎn)就是應(yīng)用了采樣控制理論中的一個(gè)重要理論，沖量相等而形狀不同的窄脈沖加在具有慣性環(huán)節(jié)上時(shí)，其效果基本相同，沖量即窄脈沖的面積。 （ 2）變轉(zhuǎn)差調(diào)速 異步電動(dòng)機(jī)的轉(zhuǎn)速公式為 )1(60)1(1 sPN fsnn ???? （ 11） 由式（ 11）可以看出，調(diào)節(jié)轉(zhuǎn)差率 s，可改變電動(dòng)機(jī)轉(zhuǎn)速 n。 我國從 20 世紀(jì) 60 年代初試制成功第一只硅晶閘管以來，晶閘管直流調(diào)速系統(tǒng)也得到迅速的發(fā)展和廣泛的應(yīng)用。第三，自出現(xiàn)汞弧變流器后，利用汞弧變流器代替上述發(fā)電機(jī) —電動(dòng)機(jī)系統(tǒng)，是調(diào)速性能指標(biāo)又進(jìn)一步提高。 PWM 即脈寬調(diào)制技術(shù)，它是 利用半導(dǎo)體器件的導(dǎo)通和關(guān)斷，把直流電壓變成電壓脈沖列，控制電壓脈沖的周期和寬度以達(dá)到變壓目的，或控制電壓脈沖的周期和寬度以達(dá)到變壓變頻目的的一種控制技術(shù)。 關(guān)鍵詞 單片機(jī) AT89S51,直流電機(jī) ,脈寬調(diào)制 The Design of DC Motor Speed Control System Based On Single Chip Abstract Dc motor is one of the earliest human invention and application of the motor. Although pared with AC motor, DC motor structure plex, difficult maintenance, more expensive, but because it has a good start, braking and speed adjustment characteristics and big start torque, can be in a wide range of smooth speed regulation, economic, easy speed control, speed control with high efficiency, so the dc motor in the industrial field is still occupies an important position. Technology is the most monly used DC speed control pulse width modulation (PWM) technology, it has fast response speed, high precision of speed and speed range and low loss characteristics. In recent years due to the rapid development of digital electronic technology, there is a important means of dc speed control, puter numerical control dc speed control, it is a microprocessor as the core of the digital control system, hardware circuit standardization degree is high, the production cost is low, is not affected by temperature drift of the device, the control software ability of logic judgment and plex operation, can realize optimization is different from general linear adjustment, adaptive, nonlinear, such as intelligent control law. Design mainly introduces the single chip AT89S51 as the core control device of DC motor speed control system, DC motor speed control system, the significance of PWM based on single chip microputer control DC motor speed control method and the basic working principle and realization method of PWM. Main circuit adopts four small keyboard (to control DC motor start, stop, direction and speed) control AT89S51, then through the motor driver chip L298 to control small DC motors. In the design of the added speed detection display circuit, by CS3020 hall switch, single chip microputer AT89S51, seven segment digital tube decoding chip 74LS47 and four LED. The whole system design, the use of a large number of integrated circuit module, greatly simplify the hardware circuit and improves the system reliability and stability. Finally in the aspect of software, this paper introduces the main program, keyboard scanning subroutine, PWM signal, speed subroutine and display subroutine program. Keywords SCM AT89S51,DC motor,PWM 目錄 1 緒論 ....................................................................................................................................... 1 課題研究的背景 ............................................................................................................ 1 選題的目的和意義 ........................................................................................................ 1 研究方法 ...................................................................................................................... 2 國內(nèi)外電機(jī)控制的研究現(xiàn)狀及發(fā)展 ................................................................................ 2 PWM 變頻調(diào)速發(fā)展前景 ................................................................................................ 3 異步電動(dòng)機(jī)的調(diào)速方法 ........................................................................................3 同步電動(dòng)機(jī)的調(diào)速方法 ........................................................................................4 PWM 變頻調(diào)速 .....................................................................................................4 課題研究內(nèi)容及目標(biāo) ......................................................................................................5 小結(jié) ..............................................................................................................................6 2 直流電機(jī)調(diào)速系統(tǒng)設(shè)計(jì) ............................................................................................................7 系統(tǒng)總體方案設(shè)計(jì) .........................................................................................................7 設(shè)計(jì)思路 .............................................................................................................7 總體方案比較與選擇 ............................................................................................7 電機(jī)調(diào)速控制模塊方案比較與選擇 .......................................................................8 基本原理分析 ................................................................................................................ 9 直流電機(jī)的調(diào)速原理 ............................................................................................9 直流電機(jī) PWM 實(shí)現(xiàn)方案論證及調(diào)速原理 .............................................................9 霍爾效應(yīng)和原理簡介 .............................................