基于DSP和ARM的激光粒度儀關(guān)鍵電路設(shè)計(jì)
西安工業(yè)大學(xué) 趙丁 劉纏牢 張艷春 王雪艷
摘要： 采集電路采集到的數(shù)據(jù)經(jīng)過RS232串口傳輸給DSP，經(jīng)過DSP的運(yùn)算后，再把DSP處理后得到的結(jié)果數(shù)據(jù)RS232經(jīng)過串口傳輸給ARM處理器，在ARM處理器的觸摸屏界面上顯示結(jié)果。
Abstract：
Key words :
激光粒度儀是一種最先進(jìn)的、最具有廣泛發(fā)展前景的粒度測量儀器，它的測量原理基于米氏(Mie)散射理論。MIE散射理論是一個(gè)經(jīng)典的光散射理論，它最大的特點(diǎn)是可用于任何尺寸段顆粒的測量，但它的計(jì)算相當(dāng)復(fù)雜限制了數(shù)據(jù)處理速度及精度。
DSP技術(shù)實(shí)現(xiàn)MIE散射算法有很多優(yōu)點(diǎn)：它是專為算法計(jì)算而設(shè)計(jì)的專用CPU，所以它運(yùn)算速度很快；與通用CPU相比它成本低，所以有很好的性價(jià)比；而且它的體積小，能實(shí)現(xiàn)儀器一體化等等優(yōu)點(diǎn)。ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" 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title="ARM">ARM" title="ARM">ARM" title="ARM">ARM具有豐富的片上資源，適合嵌入式系統(tǒng)的開發(fā)，主要負(fù)責(zé)操作系統(tǒng)的運(yùn)行、任務(wù)管理和協(xié)調(diào)以及DSP的控制任務(wù)，外部可擴(kuò)展多種外設(shè)，如通用串口、LCD顯示屏、以太網(wǎng)接口。
1 系統(tǒng)總體設(shè)計(jì)及工作原理
1．1 激光粒度儀工作原理
激光粒度儀的組成框圖如圖1所示。
激光粒度儀中的光電探測器采集顆粒在一定角度范圍內(nèi)的散射光來得到顆粒的粒徑分布信息。由于光電探測器處在傅里葉透鏡的焦平面上，因此探測器上的任一點(diǎn)都對應(yīng)某一確定的散射角。光電探測器陣列由一系列同心環(huán)帶組成，每一環(huán)帶是一個(gè)獨(dú)立的探測器，能將投射到上面的散射光能線性地轉(zhuǎn)換成電壓，然后送給采集卡。該卡將電信號(hào)放大，再進(jìn)行A／D轉(zhuǎn)換后送入計(jì)算機(jī)，按事先編制的程序根據(jù)米氏散射理論進(jìn)行數(shù)據(jù)處理，把散射譜的空間分布反演為顆粒大小的分布。
1．2 電路系統(tǒng)的總體設(shè)計(jì)
激光粒度儀電路總體框圖如圖2所示。采集電路采集到的數(shù)據(jù)經(jīng)過RS232串口傳輸給DSP，經(jīng)過DSP的運(yùn)算后，再把DSP處理后得到的結(jié)果數(shù)據(jù)RS232經(jīng)過串口傳輸給ARM處理器，在ARM處理器的觸摸屏界面上顯示結(jié)果。
2 電路系統(tǒng)具體設(shè)計(jì)方案
2．1 數(shù)據(jù)采集電路設(shè)計(jì)
粒度儀的光電探測器是用光電池做成多元環(huán)形，多元環(huán)形光電探測器接收散射光的光能量，環(huán)形光電池把光能量轉(zhuǎn)換為光電流。然后經(jīng)過電流電壓轉(zhuǎn)換器，把電流信號(hào)轉(zhuǎn)換為電壓信號(hào)。再經(jīng)過放大電路放大，然后輸入到A／D轉(zhuǎn)換器，將模擬信號(hào)轉(zhuǎn)換為數(shù)字信號(hào)。然后把數(shù)字信號(hào)輸入到C805lF320單片機(jī)，單片機(jī)然后再傳給DSP進(jìn)行處理，如圖3所示。
系統(tǒng)的硬件組成分為以下幾個(gè)部分：環(huán)形光電探測器、數(shù)據(jù)選擇部分、電流電壓轉(zhuǎn)換部分、運(yùn)算放大部分、模數(shù)轉(zhuǎn)換部分和中央單片機(jī)控制部分。
?、倌M多路選擇器選用ADG506，它精度高，為1mV，抗干擾能力強(qiáng)，功耗低，價(jià)格便宜；
?、陔娏麟妷恨D(zhuǎn)換電路有起濾波作用的電容及可調(diào)電阻，有利于調(diào)整電路參數(shù)；
③濾波放大電路的二階Butterworth低通濾波器截止頻率為10Hz，主要濾除工頻干擾；
?、苣?shù)轉(zhuǎn)換電路采用的芯片是TLC2551，此芯片是14位A／D，輸入電壓范圍為：O～5V；理論采集精度可達(dá)0．3mV，受實(shí)際測試條件所限制實(shí)際測試精度可達(dá)0．8mV；A／D轉(zhuǎn)換時(shí)間為10m，采集速度很高；此芯片抗干擾能力強(qiáng)，功耗低，性價(jià)比高；
?、菘刂齐娐凡捎肅8051F320作為采集電路的控制芯片，它片上資源豐富，主頻高可達(dá)25MHz，而且開發(fā)簡單，性價(jià)比高。單片機(jī)采集來的數(shù)據(jù)通過串口發(fā)送給DSP芯片。
2．2 DSP運(yùn)算電路的設(shè)計(jì)
DSP作為一種用的數(shù)字信號(hào)處理器，自從問世以來，DSP就以數(shù)字器件特有的穩(wěn)定性，可重復(fù)性，可大規(guī)模集成，特別是可編程性和易于實(shí)現(xiàn)自適應(yīng)處理的特點(diǎn)，給數(shù)字信號(hào)處理的發(fā)展帶來了巨大的機(jī)遇。
激光粒度儀的采集電路采集來的數(shù)據(jù)通過RS232串口傳送給DSP處理器，經(jīng)過DSP進(jìn)行算法運(yùn)算，運(yùn)算完成后再通過RS232串口傳送給嵌入式ARM處理器顯示結(jié)果。原理框圖如下圖4所示：
?、貲SP芯片選用TMS320C5416，TMS320C5416采用改進(jìn)的哈佛結(jié)構(gòu)，具有以下優(yōu)點(diǎn)：具有高度并行性和專用硬件乘法器和加法器的CPU設(shè)計(jì)，芯片性能大大提高；程序存儲(chǔ)器和數(shù)據(jù)存儲(chǔ)器是相互獨(dú)立的存儲(chǔ)器，每個(gè)存儲(chǔ)器獨(dú)立編址，獨(dú)立訪問。本系統(tǒng)中設(shè)置了16路數(shù)據(jù)總線，32路地址總線，其余的為控制總線。
②串并數(shù)據(jù)轉(zhuǎn)換采用的芯片為TLl6C752B，此芯片有兩個(gè)串口控制器，控制器A和控制器B。D00到D07為8位數(shù)據(jù)總線，RXA和TXA與RXB和TXB分別為A口與B口的數(shù)據(jù)發(fā)送端口和數(shù)據(jù)接收端口。CSA和CSB分別為A口和B口的片選端口。
?、跼S232電平轉(zhuǎn)換電路，采用的電平轉(zhuǎn)換芯片為MAX3160它把3．3V的TTL電平轉(zhuǎn)換為RS232電平。
2．3 ARM顯示電路的設(shè)計(jì)
三星公司開發(fā)的S3C2440A是一款以ARM920T為內(nèi)核的嵌入式微處理器，它的最高工作頻率達(dá)433MHz，內(nèi)含3通道的異步串行口，USB主、從單元設(shè)備接口，攝像頭接口，觸摸LCD／TFT控制器等眾多片上外設(shè)接口。LCD屏TD035STED2為3．5英寸，屏幕分辨率為320×240，能提供262K中色彩。
2．4 PCB設(shè)計(jì)
PCB設(shè)計(jì)采用的設(shè)計(jì)軟件為Protel99，PCB設(shè)計(jì)的關(guān)鍵是：模擬電路部分要具有很好的抗干擾能力和高可靠性。提高電路的抗干擾能力的方法有：①元器件布局要合理；②布線要合理；③覆銅要合理；④金屬殼接地屏蔽等。
3 實(shí)驗(yàn)結(jié)果分析
在完成電路系統(tǒng)設(shè)計(jì)的基礎(chǔ)上，進(jìn)行激光粒度儀實(shí)驗(yàn)。在相同環(huán)境、相同采集電路、相同Mie算法條件下，分別用標(biāo)準(zhǔn)P4臺(tái)式機(jī)和DSP+ARM電路進(jìn)行實(shí)驗(yàn)。實(shí)驗(yàn)樣品采用滿足R-R單峰分布的粒徑范圍為O．1～100μm的碳酸鈣。
以上兩種方式分別連續(xù)20次測試，相對于標(biāo)準(zhǔn)樣品，實(shí)測d50誤差在±3％，d10和d90誤差在±5％之內(nèi)，重復(fù)精度在±3％以內(nèi)，說明采集精度達(dá)到了儀器標(biāo)準(zhǔn)。實(shí)驗(yàn)驗(yàn)證，此系統(tǒng)設(shè)計(jì)方案比標(biāo)準(zhǔn)P4機(jī)運(yùn)算至少快10s。
4 結(jié)束語
本文將DSP的高速處理能力和ARM得管理能力結(jié)合起來，使整個(gè)系統(tǒng)在結(jié)構(gòu)上獲得最大的靈活性。高性能DSP可以滿足運(yùn)算性能方面的需要，而ARM的可控性?？梢越鉀Q觸摸顯示采集結(jié)果。同時(shí)減小了儀器體積，提高了運(yùn)算速度。
來源：現(xiàn)代電子技術(shù)
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