stude
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Fi
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clusio
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gacustomdesig
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dictatesthattemperaturesetti
gsareusuallykeptco
sta
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o
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dovershoot
2
fAlthough
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si
Table1itwasclearthatthecustomerdesireddigitaldisplaysofsetpoi
ta
dactualtemperaturesa
dthatsetpoi
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g3SystemDesig
Therequireme
tsfordigitaltemperaturedisplaysa
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te
tryalo
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oughtodictatethatamicroco
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islikelythemostappropriateFigure2showsablockdiagramofthestude
ts’desig

3
fThemicroco
trolleraMotorolaMC68HC705B166805forshortistheheartofthesystemItacceptsi
putsfromasimplefourkeykeypadwhichallowspecificatio
ofthesetpoi
ttemperaturea
ditdisplaysbothsetpoi
ta
dmeasuredchambertemperaturesusi
gtwodigitseve
segme
tLEDdisplaysco
trolledbyadisplaydriverAllthesei
putsa
doutputsareaccommodatedbyparallelportso
the6805Chambertemperatureisse
sedusi
gaprecalibratedthermistora
di
putviao
eofthe6805’sa
alogtodigitali
putsFi
allyapulsewidthmodulatio
PWMoutputo
the6805isusedtodrivearelaywhichswitchesli
epowertotheresistiveheateroffa
do
Figure3showsamoredetailedschematicoftheelectro
icsa
dtheiri
terfaci
gtothe6805ThekeypadaStorm3K041103hasfourkeyswhicharei
terfacedtopi
sPA0PA3ofPortAco
figuredasi
putsO
ekeyfu
ctio
sasamodeswitchTwomodesaresupportedsetmodea
dru
modeI
setmodetwooftheotherkeysareusedtospecifythesetpoi
ttemperatureo
ei
creme
tsita
do
edecreme
tsThefourthkeyisu
usedatprese
tTheLEDdisplaysaredrive
byaHarrisSemico
ductorICM7212displaydriveri
terfacedtopi
sPB0PB6ofPortBco
figuredasoutputsThetemperaturese
si
gthermistordrivesthroughavoltagedividerpi
AN0o
eofeighta
alogi
putsFi
allypi
PLMAo
eoftwoPWMoutputsdrivestheheaterrelay
4
fSoftwareo
the6805impleme
tsthetemperatureco
trolalgorithmmai
tai
sthetemperaturedisplaysa
daltersthesetpoi
ti
respo
setokeypadi
putsBecauseitis
otcompleteatthiswriti
gsoftwarewill
otbediscussedi
detaili
thispaperTheco
trolalgorithmi
particularhas
otbee
determi
edbur