Introduction to Digital Communication | Electronics Textbook

In the design of large and complex digital systems, it is often necessary to have one device communicate digital information to and from other devices. NetworkSites: Latest News TechnicalArticles Latest Projects Education Latest News TechnicalArticles MarketInsights Education LogIn Join Login JoinAAC Orsigninwith Facebook Google LinkedIn GitHub     0:00 / 0:00 Podcast Latest Subscribe Google Spotify Apple iHeartRadio Stitcher Pandora TuneIn Menu Articles Latest News Projects TechnicalArticles IndustryArticles IndustryWhitePapers Forums Latest HardwareDesign Embedded&Programming Education Math&Science Community Education Textbooks VideoLectures&Tutorials Worksheets IndustryWebinars VirtualWorkshops Tools Calculators PartSearch TestEquipmentDatabase BomTool ICDesignCenter Videos Latest NewProducts VideoTutorials On-DemandWebinars TechChats VirtualWorkshops Datasheets Giveaways Industry Tech Days Podcast Connectwithus NetworkSites: Textbook IntroductiontoDigitalCommunication JoinourEngineeringCommunity!Sign-inwith: Home Textbook Vol.IV-Digital DigitalCommunication IntroductiontoDigitalCommunication PagesinChapter14 IntroductiontoDigitalCommunication NetworksandBusses DataFlow ElectricalSignalTypes OpticalDataCommunication NetworkTopology NetworkProtocols Practicalconsiderations-DigitalCommunication IntroductiontoDigitalCommunication Chapter14-DigitalCommunication PDFVersion Inthedesignoflargeandcomplexdigitalsystems,itisoftennecessarytohaveonedevicecommunicatedigitalinformationtoandfromotherdevices.Oneadvantageofdigitalinformationisthatittendstobefarmoreresistanttotransmittedandinterpretederrorsthaninformationsymbolizedinananalogmedium. Thisaccountsfortheclarityofdigitally-encodedtelephoneconnections,compactaudiodisks,andformuchoftheenthusiasmintheengineeringcommunityfordigitalcommunicationstechnology.However,digitalcommunicationhasitsownuniquepitfalls,andtherearemultitudesofdifferentandincompatiblewaysinwhichitcanbesent. Hopefully,thischapterwillenlightenyouastothebasicsofdigitalcommunication,itsadvantages,disadvantages,andpracticalconsiderations. Supposewearegiventhetaskofremotelymonitoringthelevelofawaterstoragetank.Ourjobistodesignasystemtomeasurethelevelofwaterinthetankandsendthisinformationtoadistantlocationsothatotherpeoplemaymonitorit. Measuringthetank’slevelisquiteeasy,andcanbeaccomplishedwithanumberofdifferenttypesofinstruments,suchasfloatswitches,pressuretransmitters,ultrasonicleveldetectors,capacitanceprobes,straingauges,orradarleveldetectors. ExampleofAnalogCommunication Forthesakeofthisillustration,wewilluseananaloglevel-measuringdevicewithanoutputsignalof4-20mA.4mArepresentsatanklevelof0%,20mArepresentsatanklevelof100%,andanythinginbetween4and20mArepresentsatanklevelproportionatelybetween0%and100%. Ifwewantedto,wecouldsimplysendthis4-20milliampanalogcurrentsignaltotheremotemonitoringlocationbymeansofapairofcopperwires,whereitwoulddriveapanelmeterofsomesort,thescaleofwhichwascalibratedtoreflectthedepthofwaterinthetank,inwhateverunitsofmeasurementpreferred.     Thisanalogcommunicationsystemwouldbesimpleandrobust.Formanyapplications,itwouldsufficeforourneedsperfectly.But,itisnottheonlywaytogetthejobdone. Forthepurposesofexploringdigitaltechniques,we’llexploreothermethodsofmonitoringthishypotheticaltank,eventhoughtheanalogmethodjustdescribedmightbethemostpractical. Theanalogsystem,assimpleasitmaybe,doeshaveitslimitations.Oneofthemistheproblemofanalogsignalinterference.Sincethetank’swaterlevelissymbolizedbythemagnitudeofDCcurrentinthecircuit,any“noise”inthissignalwillbeinterpretedasachangeinthewaterlevel. Withnonoise,aplotofthecurrentsignalovertimeforasteadytanklevelof50%wouldlooklikethis:     Ifthewiresofthiscircuitarearrangedtooclosetowirescarrying60HzACpower,forexample,inductiveandcapacitivecouplingmaycreateafalse“noise”signaltobeintroducedintothisotherwiseDCcircuit. Althoughthelowimpedanceofa4-20mAloop(250Ω,typically)meansthatsmallnoisevoltagesaresignificantlyloaded(andtherebyattenuatedbytheinefficiencyofthecapacitive/inductivecouplingformedbythepowerwires),suchnoisecanbesignificantenoughtocausemeasurementproblems:     Theaboveexampleisabitexaggerated,buttheconceptshouldbeclear:anyelectricalnoiseintroducedintoananalogmeasurementsystemwillbeinterpretedaschangesinthemeasuredquantity. Onewaytocombatthisproblemistosymbolizethetank’swaterlevelbymeansofadigitalsignalinsteadofananalogsignal.Wecandothisreallycrudelybyreplacingtheanalogtransmitterdevicewithasetofwaterlevelswitchesmountedatdifferentheightsonthetank:     Eachoftheseswitchesiswiredtocloseacircuit,sendingcurrenttoindividuallampsmountedonapanelatthemonitoringlocation.Aseachswitchclosed,itsrespectivelampwouldlight,andwhoeverlookedatthepanelwouldseea5-lamprepresentationofthetank’slevel. Beingthateachlampcircuitisdigitalinnature—either100%onor100%off—electricalinterferencefromotherwiresalongtherunhavemuchlesseffectontheaccuracyofmeasurementatthemonitoringendthaninthecaseoftheanalogsignal. Ahugeamountofinterferencewouldberequiredtocausean“off”signaltobeinterpretedasan“on”signalorviceversa.Relativeresistancetoelectricalinterferenceisanadvantageenjoyedbyallformsofdigitalcommunicationoveranalog. Nowthatweknowdigitalsignalsarefarmoreresistanttoerrorinducedby“noise,”let’simproveonthistanklevelmeasurementsystem.Forinstance,wecouldincreasetheresolutionofthistankgaugingsystembyaddingmoreswitches,formoreprecisedeterminationofwaterlevel. Supposeweinstall16switchesalongthetank’sheightinsteadoffive.Thiswouldsignificantlyimproveourmeasurementresolutionbutattheexpenseofgreatlyincreasingthequantityofwiresneedingtobestrungbetweenthetankandthemonitoringlocation. Onewaytoreducethiswiringexpensewouldbetouseapriorityencodertotakethe16switchesandgenerateabinarynumberwhichrepresentedthesameinformation:     Now,only4wires(plusanygroundandpowerwiresnecessary)areneededtocommunicatetheinformation,asopposedto16wires(plusanygroundandpowerwires).Atthemonitoringlocation,wewouldneedsomekindofdisplaydevicethatcouldacceptthe4-bitbinarydataandgenerateaneasy-to-readdisplayforapersontoview. Adecoder,wiredtoacceptthe4-bitdataasitsinputandlight1-of-16outputlamps,couldbeusedforthistask,orwecouldusea4-bitdecoder/drivercircuittodrivesomekindofnumericaldigitdisplay. Still,aresolutionof1/16tankheightmaynotbegoodenoughforourapplication.Tobetterresolvethewaterlevel,weneedmorebitsinourbinaryoutput.Wecouldaddstillmoreswitches,butthisgetsimpracticalratherquickly. Abetteroptionwouldbetore-attachouroriginalanalogtransmittertothetankandelectronicallyconvertits4-20milliampanalogoutputintoabinarynumberwithfarmorebitsthanwouldbepracticalusingasetofdiscretelevelswitches. Sincetheelectricalnoisewe’retryingtoavoidisencounteredalongthelongrunofwirefromthetanktothemonitoringlocation,thisA/Dconversioncantakeplaceatthetank(wherewehavea“clean”4-20mAsignal).Thereareavarietyofmethodstoconvertananalogsignaltodigital,butwe’llskipanin-depthdiscussionofthosetechniquesandconcentrateonthedigitalsignalcommunicationitself. Thetypeofdigitalinformationbeingsentfromourtankinstrumentationtothemonitoringinstrumentationisreferredtoasparalleldigitaldata.Thatis,eachbinarybitisbeingsentalongitsowndedicatedwire,sothatallbitsarriveattheirdestinationsimultaneously. Thisobviouslynecessitatestheuseofatleastonewireperbittocommunicatewiththemonitoringlocation.Wecouldfurtherreduceourwiringneedsbysendingthebinarydataalongasinglechannel(onewire+ground),sothateachbitiscommunicatedoneatatime.Thistypeofinformationisreferredtoasserialdigitaldata. WecoulduseamultiplexerorashiftregistertotaketheparalleldatafromtheA/Dconverter(atthetanktransmitter),andconvertittoserialdata.Atthereceivingend(themonitoringlocation)wecoulduseademultiplexeroranothershiftregistertoconverttheserialdatatoparallelagainforuseinthedisplaycircuitry. Theexactdetailsofhowthemux/demuxorshiftregisterpairsaremaintainedinsynchronizationis,likeA/Dconversion,atopicforanotherlesson.Fortunately,therearedigitalICchipscalledUARTs(UniversalAsynchronousReceiver-Transmitters)thathandleallthesedetailsontheirownandmakethedesigner’slifemuchsimpler. Fornow,wemustcontinuetofocusourattentiononthematterathand:howtocommunicatethedigitalinformationfromthetanktothemonitoringlocation.   RELATEDWORKSHEETS: DigitalCommunicationWorksheet BacktoIndex TextbookIndex NetworksandBusses RelatedContent AnIntroductiontoCanonicalSignedDigitRepresentation HowtoBuildaDigitalInputandDigitalControlUsingMicrochip’sRN487xBluetoothModule IntroductiontoSoftware-DefinedRadio IntroductiontoHistogramEqualization AnIntroductiontoHarvestingSolarEnergyfromSpace PublishedunderthetermsandconditionsoftheDesignScienceLicense Comments 0Comments Logintocomment Loadmorecomments YouMayAlsoLike FollowingDialogAcquisition,RenesasGoesAfterCelenoforWi-Fi6/6EBoost byDr.SteveArar FromGPUstoDDR5Modules:CES2022KicksOffInnovationAwardsWithHonorees byJakeHertz NewSensorHarnessesEnergyFromMovementforHuman-machineInterfaces byAntonioAnzalduaJr. MicrochipSetsLooseOver608-bitMCUsforEmbeddedDesigners byJakeHertz WhattheExpansionofOpenRANMeansforTelecomHardware byvishvachi WelcomeBack Don'thaveanAACaccount?Createonenow. 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