Build the long range Laser Spy systemWord文档格式.docx
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Build the long range Laser Spy systemWord文档格式.docx
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sfirstelectronicinstrument,awandoperatedsynthesizernamed"
TheTheremin"
afterhim.
TheLaserSpySystemgoesbyseveralnamessuchastheLaserMicrophone,LaserListener,LaserBug,WindowBounceListenerandafewsimilarnames.TheLaserSpycertainlyworkswellunderidealconditions,butithasmanystrengthsandweaknessesthatwillbediscussedinthisplan.BuildingyourownLaserSpyisbyfarthebestwaytoexperimentwiththistechnologyasyoucanadjustthedesigntosuityourneeds,ratherthanforkingoverhundredsorthousandsofdollarsforanassembledkitthatwilllikelybefarinferiortoonethatyoucanbuildyourself.ManyofthekitsIhaveseenforsaleovertheInternetnotonlyusedatedtechnology,buttheyincorrectlystatethatthesystemusesamodulatedlaserbeamtoconvertwindowvibrationsintosound,whichissimplynotthecase.Let'
sputthemysteriestorestonceandforallandbuildaworkingLaserSpySystemfromthegroundupandexplorethefunctionalityofeachsubsystemthatmakesaworkingunit.
WewillbestartingwithanultrabasicproofofconcepttestsystemthatwillshowyouhowtheLaserSpyconvertsvibrationintosoundandhowcarefulalignmentofboththelaserandreceiverarerequiredforoptimalperformance.Ironically,themostbasicconfigurationmayprovetobethemostuseful,andthe$20youspendinpartscouldcreateasystemthatworksaswell(orbetter)thansomeoftheonesthatareforsaleontheinternetforthousandsofdollars.Asyouwillfindout,thekeytospyingwithalaserbeamisinthealignmentandreceptionofthebeam,notsomemagicalblackboxfulloffancyfiltersandopticalcomponents.
Figure1-Youwillneedsometypeoflasertobounceoffofthetargetwindow
TheobviousfirstcomponentintheLaserSpysystemisthelaser,whichwilltargetadistantreflectiveobjectandsendthebeambacktoyourreceiverfordecoding.Beforediggingdeepintothisproject,letmeexplainhowthissystemworks,anddispelsomeofthemythsthatarecirculatingontheinternetregardingtheoperationofthisdevice.Firstofall,theselaserspyingdevicesdoNOTworkonmodulationofthelaserbeamlikesomelasercommunicationdevices.Modulationofthelaserbeamisimpossiblebecauseitwouldtakesometypeofcircuitryinstalledinthelaserdrivertoactuallymodulatetheintensityofthebeam,andthelaserisgoingtobeinstalledatyourlocation,notthetargetlocation.Theprincipalthatisatworkhereisnotmodulation,butmovement!
Asthelaserreflectsfromthetargetwindow,theslightvibrationsfromconversationsornoisethatvibratethewindowscauseaveryslightchangeinpositionofthereturninglaserbeam.Thischangeinpositionisconvertedintovoltageasthesensorinthereceivercatchesthereturninglaserbeam.Thisiswhytheoptimaloperationofthereceiverrequiresthelaserbeamtobeslightlyoffsetfromthephototransistoraswillbeshown.Somovement,notmodulationtheprincipalonwhichthissystemoperates.
Youcanuseanylaseryoulikeforthisproject,andtherewillbenoqualitydifferencewhatsoeverbetweenastate-of-theartlablaseranda$2pointer.Theonlydisadvantagetousingacheaplaserpointeristhatyouwillhavetomodifyitforanexternalbatterypackifyouplantohaveitonformorethanafewminutesatatime,butthatisaneasytask.Also,avisibleredorgreenlaserwillnotallowforcovertoperationduetothefactthatitisveryeasytopinpointthesourceofalaserbeam,especiallyatnight.Forthisreason,avisiblelaserisusedforinitialdaytimetargetingandthenaninvisibleinfraredlaserisswitchedforoptimallongdurationandnighttimeoperation.Ofcourse,thisalldependsonyourintendeduse,andfordemonstrationpurposesavisibleredlaserisbest.
Figure2-Asmallspeakerwillbeusedtosimulateavibratingwindow
ThefirsttimeIexperimentedwithalaserspyingdevicewasinthe1980swhenIfoundaDIYarticleinanelectronicsmagazine.Laserswerehuge,expensivebeastsbackthen,butIwasnerdyenoughtohaveonetomessaroundwithandfollowedtheinstructionsinthearticle.Intheend,thesystemwasfoundtobe100%useless,andrumoratthetimesuggesteditwasalljustahoax.Whathappenedwasthatthearticlefailedtomentionthatascoolasthisdevicewas,itwasextremelydifficulttosetupintherealworld,especiallywhentryingtobouncefromadistantwindow.BelievemewhenIsaythatthisdevicedoesindeedwork,butusingittospyacrossthestreetwillrequireaseriousamountofsetup,finetuningandpatience.Tobeperfectlyhonest,yourchancesofsimplybeamingtowardyourneighbor'
swindowandhearinganythingareabout1,000to1againstyou.Somanyfactorshavetobeinyourfavor,suchasthetypeofwindow,thealignmentofthestructure,thetimeofday,thelevelofsound,andmostly,yourpatiencelevel.Ihavedoneasuccessfulwindowbouncefromacrossacitystreet,butitwasNOTaneasytask,sokeepthatinmind.Anysitesellingthisdeviceinkitorplansformclaimingthatitis"
pointandshoot"
shouldbedeletedfromyourfavoritesinahurry!
Tocreatea"
testwindow"
toallowthedeflectionofthelaserbeam,asmallspeakerisconnectedtosomeaudiosourcesuchasaradioorcomputerheadphoneport.Don'
tworryabouthowloudtheaudiosourcewillbe;
aslongasyoucanjustbarelyhearthesoundonthespeaker,itwillbegoodenough.Anysmallradioorportablemusicsystemwillhaveaheadphonejackthatyoucanconnecttoyourspeaker.Thesizeofthespeakerisalsonotimportantaslongasitislargeenoughsothatyoucanglueasmallbitofmirrortothecenterconetoallowasurfacetodeflectthelaserbeam.Somespeakersalreadyhaveachromedomeinthecenter,soifyoucanfindonelikethat,thenyouwillnotneedtousethemirror.Soldertheappropriatejacktothespeakerterminals;
thiswilllikelybea1/8inchheadphonejack.
Figure3-Addareflectivesurfacetothecenterofthespeaker
Anysmallpieceofahighlyreflectivesurfacesuchasamirrorcanbeusedtodeflectthelaserbeamduringthesetests.Amirrorworksbest,andapiececanbesnappedfromanoldmirrorusingpliersorasmalldentalmirrorcanbetakenapartfortoremovethesmallroundmirrorfromtheplastichousing.Ahotgluegunorevensomedoublesidedtapecanbeusedtogluethesmallmirrorsectiontothecenterofthespeaker.Thesizeofthemirrorisnotimportantsincethelaserbeamwillonlybeafewmillimetersacrosswhenitstrikesthesurface.Ifyouintendtosnapabitoffalargermirror,useaclothorpapertoweltowrapthecornersothatsmallsliversofglassdonotflyfromthemirrorasyoubreakit.Ahighlyreflectiveplasticormetalsurfacewillalsoworkforthisexperiment,andevenashinydimewilldothejobinapinch.
Figure4-Feedinganaudiosourceintothespeaker
Thespeakerneedstobedrivenbysomeaudiosource,butthelevelshouldbesolowthatyoucanonlyhearitwhenyourearisrightnexttothespeaker.Thegoalistorecreatethesameconditionsthatyouwillbedealingwithduringyourcovertspyingoperations,sothereflectivesurfaceshouldjustbarelybevibrating.Aportableaudioplayerisperfectforthistestbecauseithasalowpoweramplifierandwillrunforhoursatatime.Setyourplayertoloopindefinitelyandthenadjustthevolumeaslowasitwillgountilyoucanjustbarelyheartheoutputfromthespeaker.
Figure5-Creatinganeasytoalignspeakerbase
Thealignmentofthelaserfromthesourcetothetargetandbackisnotatrivialtask,andasyouincreasethedistancefromthelasertothetarget,youalsoincreasetheerrorlevel.At500feet,thebeamwillbecomesosensitivetodisplacementthatyouwillhavetobecarefulwhenmovingaroundthelaserbecausethedeflectionofthefloorinsideyourhomewillbeenoughtothrowthebeamoutaninchormore.WhenIfinallymanagedtosetupasuccessfullongrangeconfiguration,Ifoundthatthealignmentwassosensitivethatevenapassingcarwouldcreatewavesinthesystemduetothevibrationsbetweenthehouseandtheroad.ThelaserSpyDeviceiscertainlycapableofworkingformanyhundredsoffeetaway(evenacrossafewcityblocks),butvibrationwouldbecomesocriticalthatyouwouldprobablyneedtohaveeverythingmountedonanextremelyheavyconcreteormetalbasesecuredtotheground.Thesearethingsyouwillfindoutasyouexperimentwiththisproject.
Tomakeyourlifeeasywhenexperimentingwiththebasicindoorsetup,createsomekindofeasilyadjustablespeakerstandlikemineusinganoldwebcambaseoradjustablebenchvice.TheabilitytomovethespeakertoanyangleandsecureitwillbekeytotestingtheoperationofyourLaserSpydeviceasyoubuildit.Thetargetinglaserwillalsoneedsomekindofadjustablebaseaswell.
Figure6-Theadjustablewindowpanesimulatorreadytouse
Theadjustabl
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