Specifications

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AnRS232isusedtoconnecttheDigiwiththePIC16F877.AnI²Ctemperaturesensorchipwassoldered

ontothePIC.TheteamusedBoostCasthecompilerandSourceboostastheintegrateddevelopment

environmenttoprogramthePIC.ThePICprovidesaninterfacetoanHVACcircuit.Thereisa design

fromlastyearfortheHVACinterface,howeverwewillreviseittomakeitcompatiblewithProfessor

Dozier’sHVACunit.

Theteamintegratedtwotypesofinputstothesystem.Thefirstinputcomesfromafourbuttonkeypad

whichcontrolsthermostatsetpointtemperaturechange,automationmodeandthermostatsettings.

Thesecondinputcomesfromathreewayswitchwhichcontrolsthemodesofthethermostat.The

automaticmodeallowstheusertosetthedesiredtemperatureusingtheserver.TheDigireceives

commandsfromthehomeserveroveran802.11bhomewirelessnetwork.Thenitautomatically

changestoholdmode.Inholdmode,thethermostatissetatthedesiredtemperatureuntilthenext

inputcomesfromthehomeserver.Whenanewtemperaturesetpointisscheduled,themodeis

switchedbacktoautomatic.Inmanualmode,allcommandsfromtheserveraredisabled.Thesetpoint

temperaturecanonlybechangedthroughthekeypad.

CommercialThermostatIntegration

Thereasonsforusingacommercialthermostatareprofessionalpackagingandexistingcontroland

networkfunctionality.Atthispoint,therearethreecommunicatingthermostatsthatareparticularly

promisingforourproject.Allthreearecompatiblewith1heat—1cooland2heat—2coolgas/electric

and2heat—1cooland3heat—2coolheatpumpHVACsystems.TheyalsohaveeitherRS‐485orRS‐

232communicationcapabilities.

OmnistatZfromHomeAutomationInc.(HAI)

TheOmnistat‐Zthermostatoffers5‐1‐1programmabilityfor

weekdays,Saturday,andSunday.Thekeypadinterfaceis

straightforwardwithbuttonsfortemperatureup/down,mode,

program,hold,andfan.TheOmnistatoffersseveraldifferentmodes

ofcommunication,includingRS‐232communicationwithaPCor

wirelesscommunicationviaZ‐WavetechnologywiththeLevitonVizia

RFtoRS‐232interfacemodule.Itusespowerfromthe24VACHVAC

commonline.OmnistatmodelswithoutZ‐Wavecapabilitiescost

$180‐220(dependingonHVACsystem),andtheZ‐Wavecapablemodelscost$280‐350andtheLeviton

Viziaserialbridgecosts$100.Documentationisfairlyeasytofind,andtheproductsareeasytofind

fromhomeautomationvendors.

Source:http://www.homeauto.com/Products/Omnistat/rcseries.asp

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