8/12/2019 Two Channel Pc Based Oscilloscope Usb

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http://www.circuitvalley.com/2011/07/two-channel-pcbased-oscilloscope-usb.html

Two-Channel PC ased !scilloscope "#

$nroduction

More and more experiments are now ‘PC-assisted.’ Also conventional acquisition systems are veryexpensive. Since portable PCs are today common and a US lin! is a better solution"ere we present anoscilloscope usin# US port o$ t"e PC t"at operates at up to %& !'( wit" )%*+ input volta#e. ,t "as muc"more improved $eatures t"an t"e PC-based oscilloscope . "e oscilloscope uses ,C P,C%/011& $romMicroc"ip as t"e main controller2 w"ic" ma!es t"e oscilloscope compact as t"ere is no need o$ additionalpower supply $or t"e entire circuit board.

Circuit description

  At t"e "eart o$ t"is oscilloscope is US0.&-compliant microcontroller P,C%/011& $rom Microc"ip. 3oucan also use ,C%/0441 in place o$ P,C%/011&. Speci$ications o$ t"is microcontroller are5-%eatures o& 1'%2((0

Programming %. Up to 60 ! o$ $las" memory2 0! 7AM and 01*-byte 88P79M0. 8xtended instruction set :optimised $or ‘C’ compiler;6. x sin#le-cycle multiplier 4. Sin#le-supply serial pro#rammin# and easy debu##in#USB transceiver %. US%.% and 0.& $rom %.1 M<s to %0 M<s0. ,soc"ronous2 bul! and interrupt trans$er modes6. % ! o$ access 7AM usable wit" 60 endpoints :*4 bytes eac";Multiple oscillator and power modes%. /rom internal 6% !'( to external 4 M'( wit" P==0. Possible so$tware switc"in# between ‘run2’ ‘idle’ and sleepmodes. ,n sleep mode2 current is down to &.% >A.

6. ?ide operatin# volta#e ran#e :0.&+ to 1.1+;. Use$ul $or batteryoperations.Complete set of classical peripherals%. Several input<output :,<9; ports2 $our timers wit" capture<compares0. Sync"ronous and async"ronous en"anced modules6. Streamin# parallel port4. %&-bit A@C module wit" up to %6-c"annel multiplexer.

"is microcontroller "as a US0.&-compliant transceiver and a CPU runnin# up to %0 M,PS.

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avobe $i#rue s"ows t"e circuit o$ t"e two-c"annel PC-based oscilloscope. MCP*S% $rom Microc"ipec"nolo#y is an analo#ue pro#rammable #ain ampli$ier t"at is well suited to drivin# analo#ue-to-di#italconverters :A@Cs; and an analo#ue input to a P,C microcontroller. wo MCP*S% pro#rammable #ainampli$iers :,C4 and ,C1; ma!e it possible to c"oose t"e input ran#es $or eac" o$ t"e two c"annels2 byselectin# a #ain $rom %5% to 605%. "e ampli$iers are small2 c"eap and easy to use. A simple t"ree-wire serialperip"eral inter$ace :SP,; allows t"e P,C to control t"em t"rou#" pins 12 * and B.

"e MCP*S% ampli$ier is desi#ned wit" CM9S input devices. ,t is desi#ned to not ex"ibit p"ase inversion

w"en t"e input pins exceed t"e supply volta#es. "e maximum volta#e t"at can be applied to t"e input pin is &.6+ :+SS; to D&.6+ :+@@;. ,nput volta#es t"at exceed t"is absolute maximum ratin# can cause excessivecurrent into or out o$ t"e input pins. Current beyond )0 mA can cause reliability problems. Applications t"atexceed t"is ratin# must be externally limited wit" a resistor to t"e input pin.:pin 6;2 w"ic" is an analo#ueinput2 s"ould be at a volta#e between +SS and +@@. "e volta#e at t"is pin s"i$ts t"e output volta#e. "eSP, inter$ace inputs are c"ip-select :CS;2 serial input :S,; and serial cloc! :SCE;. "ese are Sc"mitt-tri##ered2 CM9S lo#ic inputs.

  "e only disadvanta#e is t"at t"ese ampli$iers accept only positive si#nals. "at’s w"y volta#e-s"i$tin#ampli$iers =/616 :,C0A and ,C6A; are used2one eac" $or eac" c"annel input :see /i#. %;. "e =/616 is aF/8 input operational ampli$ier wit" an internally compensated input o$$set volta#e. "e F/8 input deviceprovides wide bandwidt"2 low input bias currents and o$$set currents. "is volta#e-s"i$tin# ampli$ier results ina "i#" input impedance and an attenuation $actor o$ %54.1. A )%*+ input si#nal is t"en s"i$ted to t"e&-1+

ran#e w"en t"e pro#rammed #ain is %5%.

  wo "alves o$ t"e =/616 :,C0 and ,C6; are used as volta#e $ollowers to provide a low-impedances"i$tin# volta#e :+re$; to t"e pro#rammable ampli$iers. "is volta#e must be precisely adGusted wit" two 4.B-

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!iloo"m presets to measure precisely 0.1+ level on t"e inputs o$ ,C0 and ,C6 w"en t"e input si#nals are#rounded.

  ecause =/616 opamps need a symmetrical supply volta#e2 a small @C-@C volta#e converter ,C=B**&:,C%; is used to $eed 1+ to =/616. ?it" its small -pin @,P pac!a#e2 it needs only two polarised capacitors.,C=B**& can be replaced wit" a MAH%&44. "e MAH%&44 and ,C=B**& are monolit"ic2 CM9S switc"ed-capacitor volta#e converters t"at invert2 double2 divide or multiply a positive input volta#e."ese are pin

compatible wit" t"e industry-standard =C%&44

!verview o& the universal serial bus

 All t"e data is transmitted on t"e @D<@- symmetrical pins usin# a variable bit rate. "e position o$ a resistor:7%6; on @D or @- allows you to c"oose between t"e $ull-speed :%0 Mbps; and lowspeed modes :%.1 Mbps;.Iote t"at t"e ,C%/011&<0411 devices "ave built-in pull-up resistors desi#ned to meet t"e requirements o$low-speed and $ullspeed speed US. "e UPU8I bit :UC/JK4; enables t"e internal pull-ups. ,n t"is proGect27%6 is not used. 8xternal pullup may also be used. "e +US pin may be used to pull up @D or @-. "e pull-up resistor must be %.1 !ilo-o"ms :)1L; as required by t"e US speci$ication

The P$C so&tware

"e pro#ram $or t"e microcontroller is written in ‘C’ lan#ua#e. MP=A .B& alon# wit" MP=AC% is usedas t"e so$tware tool $or development. "e so$tware tools can be downloaded $or $ree $rom website‘www.microc"ip.com.’ ased on Microc"ip’s application notes2 t"e pro#ram $or t"e c"ip is centered on a mainloop continually pollin# t"e US transceiver state. "is loop never stops and eac" US operation is done inone pass. All operations are initiated by t"e "ost :t"e PC;2 w"ic" ends a %*-byte command"e $irst command byte determines t"e c"ip actions. "e $our possible actions are5%. Command &"5 Clears t"e 88P79M calibration memory0. Command %"5 7eceives parameters2 and stores t"e #ain-error compensation $or t"e two c"annels.6. Command 6"5 ,nitiates a (ero calibration sequence o$ t"e two c"an "e $irst command byte determinest"e c"ip actions. "e $our possible actions are54. Command &"5 Clears t"e 88P79M calibration memory1. Command %"5 7eceives parameters2 and stores t"e #ain-error compensation $or t"e two c"annels.

*. Command 6"5 ,nitiates a (ero calibration sequence o$ t"e two c"annel.

$nstallation o& the "# driver. %. ,$ everyt"in# is $ine2 plu# t"e oscilloscope wit" a US cable to your PC :runnin# ?indows S8 or "i#"erversion;. A Nnew "ardware detectedUS0-Mini9scilloscopeO dialo#ue box must immediately appear on t"escreen.I985- "e driver $or t"is oscilloscope is not $or windows B or vista.

0. Iow you can start t"e driver installation process. o download drive clic! "ere . "e #oal is to select a#ood driver :mc"pusb.in$; by c"oosin# t"e ‘speci$ic location’ option. @on’t let ?indows ta!e a #eneric driverby de$ault.

6.?"en you are done wit" installation2 #o to ‘device mana#er’ and c"ec! w"et"er ‘US0-Mini9scilloscope’ isunder ‘ot"er device’ in ‘view devices by type option. 9t"erwise2 repeat Steps % and 0.

"ser inter&ace pro)ram and operations. A user-inter$ace so$tware written in +isual asic *2 called ‘9scilloP,C2’. 3ou can download t"is so$ware clic!"ere to download 7un t"e set up pro#ram 2 "is will automatically install t"e ‘9scilloP,C’ user-inter$acepro#ram.

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application pro#ram loo!s li!e a small di#ital oscilloscope as s"own in t"e screens"ot below. +arious settin#s$or operations are #iven in t"e $ollowin# menu bars5

%. ,nputs5 Selects t"e active c"annels0. Samplin#5 Sets time-base and number o$ samples6. ri##er5 Sets t"e tri##erin# condition4. Cursors5 Selects "ori(ontal or vertical cursor positions1. Ium5 S"ows numerical sampled values2 wit" an export command :text $ile $ormat;*. Con$i#5 Con$i#ures #ain and o$$set errors

Calibration is to be done as described below be$ore readin# t"e output si#nals on t"e monitor screen byclic!in# ‘c"annels calibration’ under ‘con$i#’ menu bar. /eed t"e input wave$orms :say2 sine2 rectan#ular2sawtoot"2 etc; $rom t"e source. Clic! ‘#o’ button. "e output wave$orm will be displayed on t"e monitorscreen. C"annel-% and c"annel-0 output wave$orms can be di$$erentiated by screen and red lines2respectively. y de$ault2 t"e time base is 0&& >s per division and amplitude is 4+ per division. 3ou can sett"ese parameters as per your requirements.

Test and calibration

  "e $irst step is to adGust t"e (ero o$$set error. Connect t"e two analo#ue inputs to t"e #round level andtune t"e two 4.B- !ilo-o"m presets until pin 0 o$ bot" MCP*S0% is at 0.1+. A more precise tunin# can beac"ieved t"rou#" ‘9scilloP,C’so$tware. C"oose t"e smallest calibration value at )&.1+ $or bot" t"e inputs.

  "e ‘(ero calibration’ command tells t"e P,C to start its own internal compensation $or all calibrations.

@on’t $or#et to connect t"e inputs to t"e #round w"ile calibratin#.

  "e second parameter to c"ec! is t"e #ain error. y clic!in# t"e ‘#ain calibration’ command2 it’s possible

8/12/2019 Two Channel Pc Based Oscilloscope Usb

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to speci$y a small correction $actor. "is can be done a$ter several measurements. 3ou "ave to !now t"eactual levels sine and trian#ular wave$orms and t"e measured levels :wit" t"e cursors; $or t"e two c"annels."e #ain error is less t"an &.% per cent. "e number o$ samples can be set between ‘%&’ and ‘1&&.’ "eminimum samplin# %& >s $or two c"annels.

Construction

assembly on a bread board.

  An actual-si(e2 sin#le-side PC layout $or t"e two-c"annel PC-based US oscilloscope circuit iss"own in /i#ure and its component layout . Since t"e circuit is compact2 t"e construction is easy.

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  ,t is advised to use ,C bases $or mountin# ,C% t"rou#" ,CB on t"e PC $or easy troubles"ootin#. "e

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US connector :C9I%; must be $irmly soldered and $ixed on t"e board. ,t is located on t"e extreme ri#"t o$t"e board :re$er /i#ure.;.

wo IC connectors can be used $or t"e input si#nals $or c"annels ‘%’and ‘02’ respectively. "e connectorscan be $ixed on t"e $ront panel o$ t"e enclosure. "e per$ormance o$ t"e oscilloscope can be improved byc"an#in# t"e P,C and its A@C wit" a $aster model. A@06 :0& MS<s; is a #ood c"oice. "is $ast2 parallel A@C converter could be used wit" a power$ul @SP P,C.

*!+,!* %irmware and PC #o&tware:-

Clic! "ere to @ownload P,C /irmwareClic! "ere to @ownload PC So$tware and @riverClic! "ere to @ownload PC /ile

I985- PC $ile optimi(ed $or "ome made process "ats w"y t"read are so t"ic!2 i$ you want toPC manu$acture by pro$essional t"e you can reduce t"e si(e $urt"er

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