基于DSP和ARM的激光粒度儀關鍵電路設計
西安工業大學 趙丁 劉纏牢 張艷春 王雪艷
摘要： 采集電路采集到的數據經過RS232串口傳輸給DSP，經過DSP的運算后，再把DSP處理后得到的結果數據RS232經過串口傳輸給ARM處理器，在ARM處理器的觸摸屏界面上顯示結果。
Abstract：
Key words :
激光粒度儀是一種最先進的、最具有廣泛發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散射理論是一個經典的光散射理論，它最大的特點是可用于任何尺寸段顆粒的測量，但它的計算相當復雜限制了數據處理速度及精度。
DSP技術實現MIE散射算法有很多優點：它是專為算法計算而設計的專用CPU，所以它運算速度很快；與通用CPU相比它成本低，所以有很好的性價比；而且它的體積小，能實現儀器一體化等等優點。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" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" 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title="ARM">ARM具有豐富的片上資源，適合嵌入式系統的開發，主要負責操作系統的運行、任務管理和協調以及DSP的控制任務，外部可擴展多種外設，如通用串口、LCD顯示屏、以太網接口。
1 系統總體設計及工作原理
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都對應某一確定的散射角。光電探測器陣列由一系列同心環帶組成，每一環帶是一個獨立的探測器，能將投射到上面的散射光能線性地轉換成電壓，然后送給采集卡。該卡將電信號放大，再進行A／D轉換后送入計算機，按事先編制的程序根據米氏散射理論進行數據處理，把散射譜的空間分布反演為顆粒大小的分布。
1．2 電路系統的總體設計
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據經過RS232串口傳輸給DSP，經過DSP的運算后，再把DSP處理后得到的結果數據RS232經過串口傳輸給ARM處理器，在ARM處理器的觸摸屏界面上顯示結果。
2 電路系統具體設計方案
2．1 數據采集電路設計
粒度儀的光電探測器是用光電池做成多元環形，多元環形光電探測器接收散射光的光能量，環形光電池把光能量轉換為光電流。然后經過電流電壓轉換器，把電流信號轉換為電壓信號。再經過放大電路放大，然后輸入到A／D轉換器，將模擬信號轉換為數字信號。然后把數字信號輸入到C805lF320單片機，單片機然后再傳給DSP進行處理，如圖3所示。
系統的硬件組成分為以下幾個部分：環形光電探測器、數據選擇部分、電流電壓轉換部分、運算放大部分、模數轉換部分和中央單片機控制部分。
①模擬多路選擇器選用ADG506，它精度高，為1mV，抗干擾能力強，功耗低，價格便宜；
②電流電壓轉換電路有起濾波作用的電容及可調電阻，有利于調整電路參數；
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；
④模數轉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0．3mV，受實際測試條件所限制實際測試精度可達0．8mV；A／D轉換時間為10m，采集速度很高；此芯片抗干擾能力強，功耗低，性價比高；
⑤控制電路采用C8051F320作為采集電路的控制芯片，它片上資源豐富，主頻高可達25MHz，而且開發簡單，性價比高。單片機采集來的數據通過串口發送給DSP芯片。
2．2 DSP運算電路的設計
DSP作為一種用的數字信號處理器，自從問世以來，DSP就以數字器件特有的穩定性，可重復性，可大規模集成，特別是可編程性和易于實現自適應處理的特點，給數字信號處理的發展帶來了巨大的機遇。
激光粒度儀的采集電路采集來的數據通過RS232串口傳送給DSP處理器，經過DSP進行算法運算，運算完成后再通過RS232串口傳送給嵌入式ARM處理器顯示結果。原理框圖如下圖4所示：
①DSP芯片選用TMS320C5416，TMS320C5416采用改進的哈佛結構，具有以下優點：具有高度并行性和專用硬件乘法器和加法器的CPU設計，芯片性能大大提高；程序存儲器和數據存儲器是相互獨立的存儲器，每個存儲器獨立編址，獨立訪問。本系統中設置了16路數據總線，32路地址總線，其余的為控制總線。
②串并數據轉換采用的芯片為TLl6C752B，此芯片有兩個串口控制器，控制器A和控制器B。D00到D07為8位數據總線，RXA和TXA與RXB和TXB分別為A口與B口的數據發送端口和數據接收端口。CSA和CSB分別為A口和B口的片選端口。
③RS232電平轉換電路，采用的電平轉換芯片為MAX3160它把3．3V的TTL電平轉換為RS232電平。
2．3 ARM顯示電路的設計
三星公司開發的S3C2440A是一款以ARM920T為內核的嵌入式微處理器，它的最高工作頻率達433MHz，內含3通道的異步串行口，USB主、從單元設備接口，攝像頭接口，觸摸LCD／TFT控制器等眾多片上外設接口。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設計
PCB設計采用的設計軟件為Protel99，PCB設計的關鍵是：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 實驗結果分析
在完成電路系統設計的基礎上，進行激光粒度儀實驗。在相同環境、相同采集電路、相同Mie算法條件下，分別用標準P4臺式機和DSP+ARM電路進行實驗。實驗樣品采用滿足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20次測試，相對于標準樣品，實測d50誤差在±3％，d10和d90誤差在±5％之內，重復精度在±3％以內，說明采集精度達到了儀器標準。實驗驗證，此系統設計方案比標準P4機運算至少快10s。
4 結束語
本文將DSP的高速處理能力和ARM得管理能力結合起來，使整個系統在結構上獲得最大的靈活性。高性能DSP可以滿足運算性能方面的需要，而ARM的可控性。可以解決觸摸顯示采集結果。同時減小了儀器體積，提高了運算速度。
來源：現代電子技術
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