Ｔemｐｅratｕre Contｒol　Using a　Ｍｉcrocoｎtroller:
Ａn Ｉnterｄiscｉｐｌinａry Undｅrｇraduaｔe Eｎgineｅring Deｓiｇn Ｐｒｏject
James S.　ＭcDｏnald
Deｐartment oｆ Engｉnｅering Ｓciｅｎce
Ｔrinitｙ Uniｖeｒsity
San Ａnｔoniｏ， ＴＸ 782１2
Abｓｔｒact：Tｈis papeｒ descrｉｂes an ｉnｔeｒdiｓｃiｐlinary　dｅsign ｐｒoject　whｉch ｗas ｄoｎe under tｈｅ author’s　supeｒvisioｎ by a gｒoup of foｕr　seniｏr studenｔs　ｉｎ ｔhe Departｍent ｏｆ Engｉneerｉｎｇ Science at Trｉnｉty Universｉty． The oｂｊective ｏf tｈe　proｊecｔ was to deveｌop a teｍｐｅratuｒe　control ｓystem ｆor an ａiｒ-fillｅｄ cｈamｂeｒ. The system　wａs　to alｌow ｅnｔrｙ of　a ｄｅsirｅd　cｈａmbｅr ｔemperatuｒe　in a prescribｅd ｒａnge　aｎd to exhｉｂｉt ove
ｒsｈoot and　ｓteady-ｓtａte　ｔeｍｐeｒature eｒror of less　ｔhan　１ dｅgrｅe　Keｌvin iｎ tｈe ａctual　chamｂeｒ　temｐerature　step responｓe.　Ｔｈｅ dｅｔails ｏf tｈe deｓiｇn developed by　thｉs grｏｕｐ　of　studｅnts, baseｄ on a Mｏｔorｏla MＣ68HC05 ｆａｍilｙ micｒocｏntroller， are dｅｓｃribｅd. The ｐｅｄagogical vａｌue of　thｅ ｐroblem is also discussed tｈrougｈ a descriｐtion of some of　the key ｓteｐｓ ｉn the ｄesign　ｐrocｅｓs.　It iｓ shｏwn thａt　tｈe solutioｎ requires broad knoｗｌeｄgｅ drawn ｆrｏm ｓｅveral engiｎeｅring diｓciplｉnes incluｄinｇ ｅlectriｃaｌ, mｅchａnｉcaｌ， and ｃontｒｏl systems　engineering．
1 Introduction
Ｔｈe desiｇn ｐrｏject ｗhich iｓ tｈe suｂjｅcｔ of thｉs ｐａpｅr oｒiｇinaｔeｄ from ａ ｒeal-woｒld apｐlicatｉon. A ｐrotoｔyｐｅ oｆ ａ micrｏsｃope ｓlide ｄｒyer hａd bｅen dｅveｌoped aroｕnd　ａｎ　OmｅｇaＴＭ ｍoｄel ＣＮ-3９0 tｅmｐerａｔure controlｌer, and the oｂjeｃｔｉvｅ ｗas ｔｏ develoｐ a　cuｓtoｍ　ｔemｐerａture　coｎtrol system ｔｏ ｒepｌａce ｔhe Oｍｅga system． The ｍoｔiｖatiｏｎ　wａs ｔ
ｈat a　cuｓｔom contｒoｌleｒ taｒｇeted　spｅciｆｉcally ｆoｒ ｔｈe　aｐpｌiｃａtiｏn　should bｅ able　ｔｏ achｉeve thｅ　saｍe functionａlity　aｔ a　ｍuch　loｗeｒ　cost，　as the Omeｇａ system ｉs uｎｎｅｃessarily versatｉlｅ anｄ eｑｕｉpped ｔo hanｄlｅ a wide variｅty　of apｐｌications．
Ｔhｅ ｍechａnical laｙouｔ of thｅ sliｄe dryer ｐrｏｔotｙpe ｉs　shoｗn iｎ Figurｅ 1.　Ｔhｅ main eｌeｍｅnt oｆ the dryer is　a lａrｇe,　iｎｓulａｔed, air-fｉllｅd ｃhambeｒ ｉn which　mｉｃroscope sliｄes， eａｃｈ ｗｉth a　tｉssue sａmpｌe　ｅnｃａsed iｎ　ｐａraｆfｉｎ, caｎ bｅ ｓet oｎ caddieｓ. In　orｄer ｔhat　the paraffiｎ mａinｔain the proｐer　ｃonsisｔenｃｙ， the tｅmperature in　the slｉde　chａmｂer must ｂe maiｎtａｉnｅd ａt　ａ　desirｅd (constant) temperatｕre． A　seｃoｎd ｃhamｂｅr (tｈe ｅleｃtrｏniｃs encｌｏsure) ｈouses a reｓisｔiｖe ｈeateｒ　ａnd　the ｔemperａtｕｒｅ contrｏlleｒ, aｎd　a　fａn　ｍｏuntｅd ｏn　ｔhe ｅｎｄ ｏf the dryｅr bloｗｓ aiｒ across ｔhe heater, carryｉng ｈeat ｉnｔo thｅ slｉdｅ　chaｍbeｒ．　Thiｓ design ｐrｏjecｔ　was ｃaｒｒieｄ ｏｕt durｉng acａｄemｉc yｅａr 19９６–9７ by ｆoｕr ｓｔuｄentｓ under ｔｈe auｔhor’ｓ ｓupervision　as a　Seｎio
r Deｓiｇｎ projecｔ　in　ｔhe Depａrtment ｏf　Enｇineｅring Science at Tｒinｉty Unｉｖersitｙ. The ｐurpose ｏf this pａpｅｒ is
to describｅ　the problem anｄ ｔhe students’　solutioｎ iｎ　soｍe detail， anｄ to diｓcuss　some ｏｆ tｈe pedagoｇｉｃａl opｐortunｉtｉes offｅｒｅd　by aｎ　inｔｅr
ｄisciplｉnａｒｙ deｓign prｏjeｃt of　thｉs　tｙpｅ. Thｅ stｕdeｎｔs’　oｗｎ ｒeｐorｔ was prｅsｅnteｄ aｔ　ｔhe 199７　Ｎａtiｏnａl Ｃonferｅｎcｅ on Unｄerｇｒaduatｅ Reseaｒch [１].　Sectioｎ 2　ｇiveｓ a more detaiｌed stａtemenｔ of　ｔｈe　problem, incｌuding perfｏrｍance　sｐeciｆiｃations, aｎd Sｅctioｎ　３ descrｉbes the studentｓ’ deｓign. Ｓecｔion 4 makes up the buｌk of the pａｐer， and ｄiscuｓses ｉｎ some　ｄetａiｌ ｓｅveｒaｌ　aspeｃｔs oｆ　the dｅsigｎ pｒocｅss ｗｈｉch offer ｕｎiquｅ pｅdaｇogical　opｐorｔｕｎities. Fiｎaｌly， Section ５ ｏffｅrs soｍe conclusions.
２ Proｂlｅm　Statemeｎt
Tｈe bａsｉc　idea of the pｒoject is ｔo ｒeｐｌace　the relｅvant parｔs of the fｕncｔioｎａlｉty　of　ａn Oｍega CN-39０ temｐeratuｒe　controｌler uｓｉng ａ cuｓtｏm－designｅd sｙstem. Ｔhe　ａpｐｌｉｃaｔion dicｔａtｅs　that ｔeｍperature ｓettings are ｕｓuaｌlｙ　kept constaｎt fｏr long　ｐeｒioｄs ｏf time, buｔ　iｔ’s　nonethelesｓ　imporｔａｎｔ tｈat step chanｇｅｓ be ｔrackeｄ in a “reasonａble” ｍanner. Thｕs ｔhe maiｎ ｒequｉrｅmentｓ boil　doｗn tｏ
·ａlloｗiｎｇ a　ｃｈamｂer tｅmperatｕrｅ seｔ－point ｔo　be　ｅnｔeｒeｄ,
·displaying boｔh ｓet－point ａnd actuａl temperａｔureｓ, and
·trackｉng stｅｐ chaｎgｅs ｉn　ｓeｔ-pｏiｎｔ tempｅraｔure　ｗｉth acceｐｔaｂle risｅ　ｔiｍe， ｓtｅaｄｙ-stａte error, and ｏvershｏｏt.
Ａltｈough　ｎoｔ expliｃiｔly a ｐart　of　thｅ speciｆicaｔions in Table １， iｔ was cｌeaｒ that the customeｒ ｄｅsiｒｅｄ digiｔal　disｐlaｙｓ of set-ｐoint anｄ ａctual　tｅmpeｒａtｕreｓ, and that　sｅt-ｐｏinｔ　teｍperatuｒe enｔry should　be ｄigital　as well (as ｏpposｅd tｏ,　ｓａy, thｒoｕgｈ　a ｐotentioｍeter ｓeｔtｉnｇ).
3 Sysｔｅｍ　Ｄesｉgｎ
The ｒequirｅments foｒ digital ｔｅmperaturｅ ｄisｐｌａyｓ and setpｏint eｎｔｒｙ aloｎe aｒe enoｕgh to dictａｔe　thaｔ　ａ micｒｏcontroｌleｒbased　dｅsｉgn ｉs　likｅly thｅ mｏst　aｐpropｒiatｅ.　Ｆigｕｒe　2 shows　ａ ｂlock　diagrａm oｆ the studentｓ’ ｄesign.
Tｈe microcoｎｔrolｌeｒ， a MoｔoｒolaMC68HC７05B1６ （680５ for　short), is ｔhe　heart　oｆ tｈe systeｍ. It aｃceｐtｓ　inｐｕｔs ｆrom ａ　ｓｉｍple foｕr-key　keypａd ｗhicｈ allｏw ｓpｅcｉficatioｎ　ｏf　the ｓeｔ-ｐoiｎｔ tｅｍperature, ａnd it disｐlays ｂｏth set-pｏiｎｔ and　mｅasｕｒed chamｂeｒ teｍｐerａtures usiｎｇ two-diｇit　ｓeveｎ-ｓeｇｍeｎt LＥD　ｄisｐｌayｓ　contrｏｌlｅｄ by a dispｌaｙ driveｒ. Aｌl thｅse inpｕts and outｐuts aｒe　accomｍodaｔeｄ ｂy paｒａlｌel pｏｒts　on ｔhe 680５. Cｈaｍber　temperaｔｕre is　sensｅd usinｇ a ｐrｅ-ｃaliｂrated tｈｅrｍistｏr ａnd inｐuｔ via ｏnｅ　of the ６80５’s ａnａlog-to-diｇitａl inｐuts. Finally, a pulsｅ-ｗidth　moduｌaｔion (PWM) outpｕｔ ｏn the 680５ is ｕseｄ　to ｄrｉve ａ reｌay whｉch swｉtｃｈes　line power　to tｈｅ resｉsｔivｅ　heaｔer ofｆ aｎd on．
design翻译Fiｇｕre 3 shｏｗs a more detａiｌed sｃhemａｔic of tｈe ｅlectroｎｉｃs and ｔheｉr ｉntｅrfacing　tｏ　ｔhｅ　6８05． Tｈｅ kｅｙpad， a Sｔoｒm 3K04110３, ｈas　fｏur keys　wｈiｃh are intｅｒfａced to　piｎs PA0｛　PA3 of　Port　A， ｃonfiguｒed as inｐｕｔs.　One ｋey functｉons aｓ　a mode sｗitｃh.　Two ｍｏｄes aｒe　suｐp
ｏrted： ｓet modｅ　and run　ｍｏde. In ｓet moｄe　two ｏf　the ｏtｈer kｅｙs　ａre used to specifｙ the　ｓet－pｏinｔ　temｐｅrａtuｒｅ:　one iｎcｒemeｎtｓ it and ｏne　decreｍeｎts．　Ｔhｅ foｕrtｈ keｙ is　uｎuseｄ　aｔ ｐｒesent. The LED diｓpｌayｓ ａｒe　drivｅn by a Haｒｒis Ｓemｉｃoｎｄuctｏｒ ＩＣM7212 ｄisplａy　ｄriver　ｉnteｒｆaced tｏ ｐins PB０{PB6 ｏf Port Ｂ，　ｃonｆｉgureｄ as outpuｔｓ. Thｅ tempeｒａtｕrｅ-senｓiｎｇ ｔhｅrmiｓｔor dｒives， ｔｈｒｏugh ａ volｔage divｉdｅｒ, pin AN0 (one of ｅiｇht　analog inputs）.　Ｆｉnalｌｙ, pin PＬMA （onｅ　oｆ ｔwo　ＰWM outputs）　driｖes the heateｒ relay.
Softwａrｅ oｎ thｅ 6805 ｉmplemｅntｓ tｈe temperａｔure coｎtrol　aｌgｏｒｉtｈm, maintains tｈe tｅｍｐeｒaｔuｒe　displays， aｎｄ altｅrs ｔhe ｓet-poｉnｔ in respoｎse　ｔｏ　ｋeypad inputｓ. Because　it　is　not coｍpｌete at ｔｈis　wｒiting, ｓｏftware ｗill ｎoｔ　ｂe diｓcｕssed in detaiｌ　in ｔhｉs pａｐer. Ｔhe control algorithm iｎ paｒticular ｈａs　ｎｏt ｂeｅn　detｅｒmiｎed， but it is　ｌｉkelｙ to bｅ a ｓimpｌe　proportional ｃontｒｏller and　ｃｅｒｔainly ｎｏｔ ｍｏrｅ　ｃomplex　than a ＰID. Some ｃoｎtrol design issｕes　ｗilｌ bｅ ｄiscussed in Sectｉoｎ　4, however.

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