set-pointandmeasuredchambertemperaturesusingtwo-digitseven-segmentLEDdisplayscontrolledbyadisplaydriver.Alltheseinputsandoutputsareaccommodatedbyparallelportsonthe.Chambertemperatureissensedusingapre-calibratedthermistorandinputviaoneofthe’sanalog-to-digitalinputs.Finally,apulse-widthmodulation(PWM)outputontheisusedtodrivearelaywhichswitcheslinepowertotheresistiveheateroffandon.Figureshowsamoredetailedschematicoftheelectronicsandtheirinterfacingtothe.Thekeypad,aStormK,hasfourkeyswhichareinterfacedtopinsPA{PAofPortA,configuredasinputs.Onekeyfunctionsasamodeswitch.Twomodesaresupported:setmodeandrunmode.Insetmodetwooftheotherkeysareusedtospecifytheset-pointtemperature:oneincrementsitandonedecrements.Thefourthkeyisunusedatpresent.TheLEDdisplaysaredrivenbyaHarrisSemiconductorICMdisplaydriverinterfacedtopinsPB{PBofPortB,configuredasoutputs.Thetemperature-sensingthermistordrives,throughavoltagedivider,pinAN(oneofe。