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Inthislecture,youwilllearnaboutwhatisinsidetheESP32chipandhowtosetupyourlaptopandtheESP32modulesothatyoucanprogramtheESP32inMicroPython.

ThemicroprocessorchipontheESP32moduleisanEspressifESP32microcontrollerchipdesignedforInternetofThings(IoT)applications.Thischipiscalledamicrocontrollerbecauseithastheprocessoritself(CPUcore),on-chipmemory,andmanyotherbuilt-incomponentsthatallowsusertoalmostbuildanentirecomputersystemononechip(calledSystem-on-ChiporSoC).

Theentirechipcanbedividedintoanumberofsub-modules.Theyare:•  CoreandMemory(brainofthechip)•  CryptographicHardwareEngines(forencryption&decryption)•  Wirelesscommunications(wifiandbluetooth)•  Powermanagementsubsystem(forlowpowerIoTapplications)•  Peripheralinterfaces(forconnectionwithotherdevices)

•  Extraflashmemory(SPIRAM)ThedatasheetoftheESP32canbefoundhere:https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf

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TheCPUcoreandmemorycontainsa32-bitXtensaLX6microprocessor,whichisasiliconIP(intellectualproperty)coredesignedandownedbyTensilica,acompanyinCalifornia.ThisblockinsidetheESP32alsocontains:•  448kBoflashmemory(ROM)thatisnon-volatile(i.e.itscontentisstoredevenif

powerisremoved)•  520kBofSRAM(staticRAM)whichisusedtostoreallvariables,heapandstackThemicroprocessorisquitepower,capableofexecuting240millioninstructions(single-core)andrunningat240MHzclock.

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OnerequirementofanIoTdeviceisultralow-power.TheESP32containsanentirelow-powermanagementsubsystemthathandlesapplicationswherespeedisNOTthemostimportantfeature.Insteaditallowsthedevicetogotosleepandwakeuponlywhennecessarytodosomebasictaskssuchastakeareadingortwo,andsendthemwirelesslyviaWiFiorBluetoothtoabase-station.Furthermore,thismodulealsocontainsaReal-timeClock(RTC)thatallowsschedulingofevents,andwakeuptheUltraLow-powerco-processor(ULP)todoitsthing!Whenevertheprocessorgoestosleep,itstoresawaywhatitsdoing(calledits“state”or“context”)inablockofrecoverymemory,sothatwhenitwakesup,theULPcanberestoredtoitsoriginalstate.

WewillnotbeusingthissubsysteminElectronics1.

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SincetheESP32isdesignedforIoTapplications,onerequirementforsuchapplicationsisprivacyandsecurity.Thereforeinformationsentorreceivedareoftenencrypted.Doingencryptionanddecryptionusingthemicroprocessorisnotonlywasteful(becauseitwon’tbeabletootherusefulthingswhileperformingencryption/decryption),itisalsoslowwhenperformingsuchtasksusingsoftware.Worse,itispowerhungry.ThereforetheESP32integratesthreedifferentencryption/decryptionengineson-chip,whichimplementthemostcommonencryption/decryptionalgorithms.Theseare:Rivest-Shamir-Adleman(RSA),SecureHashAlgorithm(SHA)andAdvancedEncryptionStandard(AES).Don’tworryexactwhattheseare–youwillhowevercomeacrosstheminmanyapplicationslaterduringyourdegreeprogram.Finally,thissubsystemalsocontainsahardwarerandomnumbergeneratorengineforanyapplicationsthatrequireshighqualityrandomnumbers.

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BeinganIoTspecificdevice,theESP32isoneofthechiponthemarkettohaveintegratedwiththemicroprocessorbothWiFiandBluetoothcommunications.Boththesecommunicationstandardsrequirebothdigitalandanaloguehardware(theradio).Again,wedonotwantyoutoworryabouttheseatthisstage.Neverthelessyouwillfindthatthissub-systemismostusefulformanystand-aloneproductsthatyoumaydesigninthefuture.WewillnotbeusingthissubsysteminElectronics1.

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Thefinalsubsystemtoconsiderislarge.ItcontainsmanyseparateIPblocksthatallowstheESP32tointerfacetotheoutsideworlddirectly.Includedhereare:•  I2Cinterface–thisiswhatweusetodrivetheOLEDdisplayontheHeltec

module•  SPIinterface–thisisafastinterfaceanditisusedtolinkwiththe4MBSPIRAM

(extractstorageforourprograms)

•  I2Sinterface–Thisisadedicatedinterfaceforaudiosignals•  UART–YoulearnedaboutthisbackinLab1andinDigitalBasicslecture•  SDIO,CAN–bothareotherdigitalinterfacesforvariousapplications•  IR–infra-redinterfaceasusedbyremotecontrol(e.g.onyourTV)•  PWM–thisgeneratesPWMsignalsfordrivingmotorsandLEDlights•  Sensorinterfaces–Temperatureandtouchsensorinterfaces

•  EH–Ethernetinterface•  DAC–8-bitdigitalconverter(usedforSIG_GENforanalogueoutputs)•  ADC–AnaloguetoDigitalconverter

ThoseshowninBLUEabovearefeaturesthatyouhaveuseorwillbeusinginElectronics1.

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TheESP32moduleyouuseisdesignedandmanufacturedbyHeltec.InadditiontotheESP32chip,themodulealsoincludea128x640.96”OLED.ItisconnectedtotheESP32usingtheI2Cinterface.(Wewilldiscussthisinterfaceduringthelectureon“Link”later.)HereisapinoutdiagramfortheHeltecmodule.YoucanfindahighqualityPDFfileofthispinoutdiagramon:https://resource.heltec.cn/download/WiFi_Kit_32/WIFI_Kit_32_pinoutDiagram_V2.pdfNotethat:

•  Almostallpinsaremultipurpose.Usercanprogramthepinsfordifferentuse.Forexamplepin26canbeusedfor:digitalinput,digitaloutput,analogueinputandanalogueoutput.

•  Thecolourcodeshowsatypeofusageforapin.Forexample,GREENisfordigitalinput(i.e.toA-Dconverter),PINKisforGeneralPurposeIO(GPIO),whichisdigitalinputoroutput,BROWNisforanalogueoutput(i.e.viaaD-Aconverter).

•  ThreeofthepinsarealreadyconnectedtoOLEDdisplayonthemoduleusingtheI2Cinterface.

•  Therearealsodedicatedpowerpins.

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TheESP32willbeprogrammedusingMicroPython.Theslideprovidesanoverviewoftheprogrammingenvironmentthatyouwillbeusing.1.  YoumustfirstloadtheMicroPythoncodeontotheESPinternalflashROM

(showninblackontheright).2.  Lateryouwillloadintotheinternalflashmemoryyourownprogramcode

(showninblue).

3.  TocontroltheESP32withuPy,youcantypedirectlyintotheREPL>>>apythoncode(suchas:println(“Helloworld!”),onelineatatime.

4.  AlternativelyyoucancreateauPyscriptandloadthisintoESP32flashRAM.5.  TocreatetheuPyscript,youwillusethePyCharmIDEonthelaptop.This

environmentalsoprovideaneditor,abilitynavigatetheprojectdirectory,communicatewithuPyREPLdirectlyviaaterminalwindow,andevenflashyourprogramcodeontotheESP32.AllthesecanbedonewithinthePyCharmIDE.

WhenyoufirstpoweruptheESP32,uPywillexecutetheboot.pyfile.Theboot.pyfilewillrunthemain.pyfile.Themain.pywillhaveonesingleuPyline:

execfile(‘user_program.py’)

Yourprogramwillbestoredintheuserprogramfile:‘user_program.py’).(Changethenameofthefiletosuit.)Alsostoredintheon-chipflashRAM(ROM)areothermodulesthatyourprogrammayuse.Forexample,youwillbeusingoled.py,whichisthedriverfortheOLEDdisplay.

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BeforeyoucanusetheESP32forLab4,youneedtofirstsetupyourenvironmentforMicroPython.Thisinvolvesquiteanumberofsteps.Asaresult,IhavedividedLab4intoPartAandPartB.PartAdoesnotteachingyoumuchexceptthatyouwillgainsomeexperienceinsettingupasoftwareenvironmentthatisfairlycomplex,andlearnabouthowtoflashprogramsontotheESP32.TheIDEyouwillbeusingiscalledPyCharm.ThisissimilartoVSC,butitisdesignedpurposefullyforPythonprogramming.ThereasonIchosePyCharmisthatithasintegratedintothisthroughaMicroPythonplug-inthenecessarytoolstorunprogramsontheESP32andtoflashnewprogramscriptstoitsmemoryfromwithintheIDE.

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MicroPythonisquitealargesystemandtherearetoomuchtolearn.Itisalsogoodifyoulearntoreadinstructionsfromwebsites,ratherthanjustbeenspoonfedbyme.So,goto:https://docs.micropython.org/en/latest/

Youwillseethispage.Therearelotsofusefuldocumentshere.Explore!

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MicroPythonprovidesmanylibraryfunctionsinordertomakeprogrammingthisboardmucheasier.Therearebasicallytwomaincategoriesoflibraryfunctions:1.  AsubsetofthestandardPythonlibraryyoucanfindeverywhere(but

implementedforMicroPython).Ofthese,thetwothatyouwouldneedare:mathandsys.

2.  ThereisabunchoflibraryfunctionsthatarewrittenfortheESP32specifically.Thethreethatyouneedare:machine,espandesp32.Themachinelibraryprovidestoplevelcontroloftheboard,andesp&esp32providedetailcontrol.machineisthemostimportantlibraryforyoutoknow.Almostallfunctionsweusesofarareimportedfromthemachinelibrary.

3.  Thereisanotherimportantmodule:time.Thisprovidesdelayinmillisecondormicroseconds(e.g.time.sleep_ms()).

4.  Thenthereisalargecollectionofperipheralspecificlibraries(theyarewrittenasobject-orientedclasslibraries).Youwillbeusingmanyfunctionsfromthese.

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Themachineclasslibrariesincludesthoseshownhere.InLab4,youusedthefollowinglibraryclasses:PWM,ADC,Pin(everything),Timer(thesearefunctionstocontrolinternaltimercircuits),I2CandUART.IhaveprovidedexamplesinLab4Bforyou.Youdon’tneedtoknowalltheselibraries.Youshouldlearnusingthisapproach:1.  Learnfromtheexamplecodeprovided.

2.  Ifthesedonotdowhatyouneed,beclearwhatfunctionyouneedtoperform.

3.  Lookforafunctioninthelibrarythatislikelytogiveyouwhatyouneeded.

4.  Failingthat,askmeoryourfriendsandclassmates,oryourteamprojectsupervisor.