基于电话线的PC远程控制家用电器外文翻译文档格式.docx
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基于电话线的PC远程控制家用电器外文翻译文档格式.docx
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INTRODUCTION
HomeAutomationthatwasintroducedinthisstudywasimplementedbydesigningthe“SmartControlSystemthatControlsAllAppliancesRemotelybyPhone”.ThedesignwasbasedontheTelephonyStandardswhichmeantthatthesystemwasqualifiedtobeinstalledonthepublicswitchingsystems.ThesystemdesignwasutilizingtheDualToneMultifrequencyDTMFsignalsthatcouldbeproducedbythetelephoneset.Thesesignalsweresentfromtheuserendthroughtheloopwiretothedestinationend,wherethecontrolsystemwasstationed.Thesystemconsistedofthreemajorparts.ThefirstpartwastheringdetectorandDTMFreceiver.ThesecondpartwastheInput/Outputinterfaceunit.ThethirdpartwasthepersonalcomputerwhichwasprogrammedwithTurboBasicSoftwaretoperformtheonlineoperations.Blockdiagramofthesystemwasshowninfigure1.
Figure1:
SmartcontrolsystemtocontrolAppliancesremotelybyphone
BRIEFOPERATIONOFATELEPHONESET:
Asummaryofthetelephonesetoperationwasgivenhereforthereadertovisualizethesystemoperation.Blockdiagramofatelephonesetisshowninfigure2.
(a)Localloop:
Eachsubscribertelephonewasconnectedtoanexchangeofficethatcontainedtheswitchingequipment,siequipmentandbatteriesthatsuppliedthedirectcurrenttooperatethetelephone.Eachphonewasconnectedtothecentralofficethroughalocalloopoftwowirescalledawirepair.OneofthewireswascalledTfortipandtheotheronewascalledRforringwhichreferredtotheTIPandRINGpartsoftheswitchusedinmanualswitch-boards.Switchesintheexchangeofficerespondedtothedialpulsesortonesfromthetelephonetoconnectthecallingpartytothecalledparty.Whentheconnectionwasestablishedthetwotelephonescommunicatedovertransformercoupledloopsusingthecurrentsuppliedbytheexchangeofficebatteries.
(b)bInitiatingacall:
Thesituationwherethe“receiver”handsetwasliftedfromitscradlewascalledtheoff-hookcondition.Theoff-hooksignalinformedtheexchangethatsomeonewantedtomakeacall.Theexchangesentadialtonetothecallerphonetoletthecallerknowthattheexchangewasreadytoacceptatelephonenumber.Thetelephonenumberwassometimesreferredasanaddress.
(c)SendingaNumber:
Sometelephonesetssentthetelephonenumbersbydialpulseswhileotherssentitbyaudiotones.Inthisstudyaudiotonetelephonesetswereused.Thesesetshadapush-buttonkeypadwith12keys.Pressingoneofthekeyscausedanelectroniccircuitinthekeypadtogeneratetwooutputtonesthatrepresentedthenumber.ThesetonesarecalledDualToneMultifrequencyDTMFsignals.
(d)ConnectingthePhones:
Theexchangeofficehadvariousswitchesandrelaysthatautomaticallyconnectedthecallerandthecalledphones.Ifthecalledphonehandsetwasoff-hookwhentheconnectionwasattemptedabusytonewasgeneratedbytheexchangeofficeandwasreturnedtothecallerphone.Otherwisearingingsignalwassenttothecalledphonetoalertthecalledparty.Atthesametimeabacktonewasreturnedtothecallertoindicatethatthefailedphonewasringing.
(e)AnsweringtheCall:
Whenthecalledpartyremovedthehandsetinresponsetoaringthelooptothatphonewasclosedandaloopcurrentflowedthroughthecalledtelephone.Theexchangeofficethenremovedtheringingsignalandtheringtonefromthecircuit.
(f)EndingtheCall:
Intodaysmostswitchingsystemsthecallwasendedtheconnectionwasreleasedonlywhenthecallingartywenton-hook.
Figure2:
Blockdiagram
SYSTEMDESIGN:
ThesystemwasdesignedtoreceiveandrespondtotheDTMFsignals.HencethecallerpartyshoulduseatelephonesetequippedwithaDTMFkeypadforsendinganumber.TelephonesetsusingtheDTMFmethodforsendingatelephonenumberwereequippedwithapush-buttonkeypadwith12keyswhichrepresentedthenumbers0through9andthesymboland.Seefigure3.PressingoneofthekeyscausedtheDTMFgeneratortogeneratetwotonesinthevoiceband300-3000Hz.Therewasalowfrequencytoneforeachrowandahighfrequencytoneforeachcolumn.Pressingkey5forexamplegenerateda770Hztoneanda1336Hztone.Byusingthedualtonemethod12uniquecombinationswereproducedfromonlyseventoneswhenthe12positionkeypadwasused.
Figure3:
DTMFKeypadandFrequencies
Thefrequenciesandthekeypadlayouthavebeeninternationallystandardizedbutthetolerancesonindividualfrequenciesvariedindifferentcountries.TheNorthAmericanstandardswere1.5forthegeneratorandf2.0forthereceiver.ThetoneshavebeenselectedcarefullysothattheDTMFreceiverintheexchangeofficewouldnotconfusethemwiththeothertonesthatmightoccuronth6line.TheseDTMFtonesfromtheexchangeofficeweretransmittedthesameasspeechoverthetelephoneline.ThispermittedustoreceivetheDTMFtonesbyoursystemsDTMFReceiverifanynumberwaspressedonthekeypad.
(a)DTMFReceiverCircuit:
ThetaskoftheDTMFReceiverwastodetectthepresenceofavalidtonepaironatelephonelineorothertransmissionmedium.Thepresenceofavalidtonepairindicatedasingledigit.Inordertogenerateavaliddigitsequenceeachtonepairshouldbeseparatedbyavalidpause.ThefollowingtableshowedtheestablishedBellsystemstandardsforavalidtonepairandavalidpause:
Low-GroupTone:
697or770or852or941Hz
High-GroupTone:
1209or1336or1477or1633Hz
FrequencyTolerance:
for(1.5%+2Hz)
AmplitudeRange:
-24.CA<
6@600Ohm
ToneDuration:
40msorlonger
PauseDuration:
Figure4showedthecompletecircuitfortheDTMFreceiver.ThecircuitemployedtheRadio-Shack276-1303DTMFReceiverIC.ItwasacompleteDualToneMultifrequencyDTMFReceivercircuitdetectingaselectablegroupof12or16standarddigits.
Figure4:
DTMFReceiverampTelephoneSourcecontroller
TheblockdiagramoftheDTMFreceiverinternalstructure.Theanaloginputsignalwaspreprocessedbya60-Hzrejectfilterapreamplifierandalowpassfiltertoemphasizethesignalpart.TheoutputofthepreprocessorstagewasthensplitintotwofrequencybandseachofwhichcontainedonlyoneDTMFtonegroup.
Theoutputofeachband-splitfilterwasamplifiedandthefollowingzero-crossingdetectorconvertedthesinusoidalsignalstosquarewaves.Thesesquarewavespassedthroughtonefrequencybandpassfilterstogeneratetheindividualfrequenciesineachtonegroup.Eachbandpassfilteroutputwasdetectedbyanamplitudedetectorandfedtoatimingcircuittodeterminethedetectionvaliditywithin40ms.Thedetectoroutputwasalsofedtoanoutputdecodertodecodethetonestotheirequivalentbinarynumbers.Thetimingcircuitryproducedthecontrolpulsesforanoutputregister.ForexamplethedatastrobefromthetimingcircuitenabledthedecoderoutputstobelatchedattheregisteroutputsD1,D2,D4,D8.Theregisteroutputsbecamevalidafteratonepairhasdetectedandtheywereclearedwhenavalidpausehasarrived.TheoutputformatwasprogrammedbytheHEX/B28pin.WhenHEX/B281theoutputwashexadecimalandwhenHEX/B280theoutputwasabinarycode.Thefollowingtablesshowedthetwooutputformats.
ABCandDwereusedforextendedkeypads.TheDataValid(DV=1)pinindicatedavalidtonepairwassensedanddecodedattheoutputpinsofD1D2D4andD8.DVremainedhighuntilavalidpauseoccurred.Asshowninfigure4theinputpins9and10ofDTMFreceiverICwereconnectedtoanIsolationtransformerwhichwasusedtoisolatethetelephonelinegroundfromthedigitalground.Pin10wastiedtothedigitalgroundwhichwastheinputground.TheRingterminalofthetelephonelinewasconnectedtooneterminaloftheIsolationtransformerandtheothertransformerterminalwasconnectedtooneendofarelay.TheotherendoftherelaywasconnectedtooneterminalofacapacitorwhichalloyedACsignalstopassthrough.ThesecondterminalofthecapacitorwasconnectedtotheTipterminalofthetelephoneline.TherelayprovidedthecontrolofconnectingtheDTMFreceivertothetelephonelineviathePC.ItalsoprotectedtheDTMFreceiverfromtheringsignalsthatcoulddamageit.Theringsignalswereintherangeof40to130Vand16to60Hz.ThetypicallU.S.valueswere90Vand20Hz.Pin4wastiedtothegroundtoenablethedetectionoftonepairs.Pin2wastheHEX/B28pinanditwastiedtohightoshowthattheoutputwasinhexadecimal.Pin3wastiedtohighwhichconfiguredtheoutputstobepushpull.Pins11617and18theoutputpinsandpin14thedatavalidDVpinwereconnectedtothe1/0interfacecardviaHEXinverters.Pin7wastheICground.Itwastiedtothedigitalgroundwhichwasprovidedfromthe1/0interfacecard.Pin15CLRDVwasalsotiedtothedigitalgroundtoshowthattheDataValidDVwasclearedbyavalidpauseonly.Pin5wastheICpowersupply5whichwasprovidedfromtheI/Ointerfacecard.TheICcrystalwasconnectedbetweenthepins11and12
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