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Fog Horn
University of New HampshireUndergraduate Ocean Research Project 20082009
4/26/2009
TeamMembers:
MathieuFeraud
DanFournier
WyattO'Day
MarcOuellette
Advisors:
KennethBaldwin,Ph.D.
AlanDrake,Ph.D.
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Table of contents
Sections
Acknowledgments Page3
I.Abstract Page4
II.Introduction Page5
III.Background Page6
IV.Methods Page7
V.Discussion Page9
a.
Drivers
Page
9
b.CaseDesign Page9
c.AmplifierCircuitDesign Page11
d.MicrocontrollerDesign Page12
e.FogHornTesting Page13
VI.Results Page15
VII.Conclusion Page19
Appendices
A.References Page21
B.MicrocontrollerCode Page22
C.Test,Measurement,andDiagnosticEquipment Page26
D.CaseSchematics Page27
E.AmplifierCircuitLayout Page33
F.
Bill
of
Materials
Page
35
G.FogSignalDesignCriteria Page36
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Acknowledgements
Thisworkistheresultofresearchsponsoredinpart,bytheNationalSeaGrantCollegeProgram,
NOAA,
Department
of
Commerce,
under
grant
#NA06OAR4170109
through
the
New
Hampshire
Sea
GrantCollegeProgram.
Thefoghorndesignteamwouldliketoacknowledgethefollowingpersonsandentities,whose
contributionsandguidancemadethesuccessfulcompletionoftheprojectpossible.
KennethBaldwin,Ph.D.
AlanDrake,Ph.D.
JenniferBedsole
Paul
Goodwin
WatermarkNavigationSystems,LLC
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I. Abstract
Audible warning signals are necessary for ensuring the safety of nautical vessels in inclement
weather conditions where a visible navigation beacon may become obscured. An engineering challenge
exists in designing a commercially viable fog horn which is simultaneously lightweight, low profile,
weather resistant, has low power consumption, and yet is powerful enough to produce an audible signal
over a great distance.
This design team has endeavored to design a fog horn prototype which meets or exceeds the
specifications set forth by the customer, while keeping the design flexible enough that the customer
may implement design changes in the future.
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II. Introduction
Warningsignalshavebeenusedforcenturiesasamethodforwarningnauticalvesselsofthe
presenceof
hazards
and
obstacles
in
open
water.
Such
signals
become
necessary
when
visibility
conditionsaresuchthatawarningbeaconcannotbeseenintimefortheshiptochangecourse. Thus,
thenauticalwarningsignal orfoghorn,asitismorecommonlyknown isaninvaluabletoolfor
navigation. Theprevalenceofoffshoreoilplatformsmakesthemodernfoghornespeciallyimportant
tomodernseafarers.
WatermarkNavigationSystems,LLCisthemanufactureranddistributorofawiderangeof
nauticalaids,includingmarkerbuoysandsignalbeacons. Watermarkfoundthatacommoncomplaint
amongsttheircustomerbasewasthelackofaninexpensive,lightweight,andlowmaintenancefoghorn.
Seeingthis
opportunity
to
meet
amarket
need
while
expanding
their
product
base,
Watermark
approachedtheUniversityofNewHampshirewiththeproposaltosponsoranundergraduateproject
teaminthedesignofsuchafoghorn.
Thoughitisrelativelysimpleinconcept,aviablefoghornpresentsuniquechallengestoateam
ofengineers. Onemustconsidertheenvironmentinwhichthehornistooperate. Thefoghornwill
constantlybeexposedtomoistureandsaltfromseawater. Itmustbeabletowithstandwindandheavy
rainsaswellasawiderangeoftemperatures. Itmustbesmallandlightenoughtomaketransportation
outtoitsinstallationsiteeconomicallyviable. Incontrast,itmustberuggedenoughtoremain
unaffectedbyaharshoutdoorenvironment. Mostimportantly,itmustproduceasignalwhichis
audibletoavesselatdistancesfarenoughtoavoidtheobstacle. Theproductionofsuchapowerful
audiblesignalcarrieswithititsownengineeringchallengesintermsofthepowerrequiredtoproduce
it.
Thus,theaimofthisprojectteamwastoapproachthisuniqueandveryrealengineering
challengeanddeviseafoghornwhichwouldmeetthespecifiedcriteriaandserveastheprototypefor
Watermarksownlineoffoghorns. Theteamconsistedofasmall,interdisciplinarygroupofengineers
whosaw
in
this
project
the
opportunity
not
only
to
innovate
but
to
also
gain
the
experience
of
having
guidedanideathroughthestagesofdesigntoemergewithamarketableproduct.
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III. Background
WhenPaulGoodwinofWatermarkproposedthefoghornprojecttotheUniversity,heincluded
in
the
project
description
several
features
that
he
expected
the
final
foghorn
to
possess.
Obviously,
the
designconstraintsmentionedearlierwerementioned. Thesespecificdesigngoalscanbeseenin
AppendixG: FogSignalDesignCriteria.
Principalamongtheseconstraintswastheproductionofanaudiblesignalofspecificduration
andloudenoughandtomeettheCoastGuardspecification. Theprimarycriteriaofthisspecification
arethatthesignalmustbeapproximately120decibelsat1meterandthatitpersistsfor2secondsover
a20secondinterval.
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IV. Methods
The exact approach that the design team would take to meet this benchmark was not
immediately clear. Many methods exist by which sound can be created. A historical investigation of
foghorns revealed that the earliest fog signals were bells. At the turn of the century, compressed air
horns such as diaphones were widely used. Most commercially available modern foghorns use
compression drivers or other electromagnetic loudspeakers to produce sound. Other methods also
exist, such as vibrating plates and piezoelectric speakers, which can produce audible signals.
The design team began by performing a feasibility study into each of these methods in order to
determine if some viable method of sound production existed beyond loudspeakers that could meet the
design criteria. The team examined four such approaches: a mechanical bell, a piezoelectric speaker, a
compressed air horn, and a method utilizing vibrating plates.
The mechanical bell idea was quickly discarded after the realization that the size of the bell
necessary to produce sound pressure levels exceeding 120 dB would be prohibitively large. The
mechanical apparatus necessary to strike the bell at the specified 20 second interval would necessitate
the use of a motor or other such electro-mechanical device which would decrease the maintenance
interval of the signal as well as significantly add to its weight and overall power consumption.
The piezoelectric speaker also proved to be an intractable approach. Though piezoelectric speakers are
small and consume very little power, the amount of sound pressure they are capable of producing is
likewise small. Suitable for applications such as hearing aids and earphones, where they can directly
stimulate the eardrum, the piezoelectric driver cannot come close to providing sound pressure levels
appropriate to our application.
Compressed air offered the team the first viable approach to meeting the audible signal criteria.
Many compressed air systems, such as the ones used on tractor trailers and locomotives, exist which
meet or exceed the 120 dB sound pressure level needed for the horn. A compressed air system
activated by a solenoid could be electronically controlled and would be well protected from moisture.
The major factor that diminishes the viability of the compressed air system is the necessity to include a
compressor on-site. Though a compressed air bottle would power the horn for a short time, the
frequency with which it would need to be recharged makes this approach prohibitive as technicians
would have to travel back and forth to the horn to replace these bottles. A compressor on site is the
only approach which makes any sense; however, a compressor is expensive, heavy, is susceptible to
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moisture, consumes a great deal of power, and necessitates routine maintenance. For these numerous
reasons, the compressed air approach was deemed to lie outside of the possible design approaches for
the foghorn.
The vibrating plate approach was lastly considered. A relatively obscure technology, it utilizes
rods affixed to a series of thin plates which are made to vibrate by quick back-and-forth movements of
the rods themselves. Few vibrating plate loudspeakers exist, and the ones that do are marketed as
high-frequency loudspeakers for audiophiles. Though they consume less power and offer a frequency
response better than that of a traditional loudspeaker, the unavailability of these devices coupled with
the complexity of manufacturing one made this an approach which the team was reluctant to explore
due to the constraints of time and budget.
Thus, the design team decided that for the factors of small size and weight, coupled with
commercial availability and ease of implementation, the use of electromagnetic compression driversmade the most sense.
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V. Discussion
Afterchoosingthecompressiondriversasthemethodtomakesound,wethenbeganbreaking
theproblem
of
making
aworking
fog
horn
prototype
into
approachable
pieces.
a.
Compression
Drivers
Awidearrayofloudspeakersarecommerciallyavailable,andthusitbecamenecessaryto
narrowthefieldfordriverswhichwouldbeappropriatetothefoghornapplication. Thefirstcriterion
whichthedriverhadtomeetwastheabilitytoprovideatleastthespecifiedsoundpressurelevelgiven
areasonablepowersignal. Secondly,thedrivermustoperatewellwithintheregionofthehornssignal
frequency. AccordingtotheCoastGuardspecification,thisincludestonesaslowas400Hzandashigh
as1.2kHz. Acriterionwhichbecameapparentafterattemptingtoorderseveraldriverswastheactual
commercialavailabilityofthedriveritself. Somedriverswerediscoveredwhichcouldmeetthe
demandsofourhorn,butwhichturnedouttobemanufacturedbyacompanythathadgoneoutof
businessorhadceasedcarryingtheproduct.
ThedriversonwhichthedesignteameventuallysettledweretheElectroVoiceID60DTheavy
dutycompressiondrivers. Thesehighpowerindustrialdriversfeaturedaruggedizeddesign,asealed
wiringcompartment,tropicalizedmetalpartsforresistancetohumidity,andweatherproofpaint. The
readyavailabilityanditsweatherresistantfeaturesmadeitideallysuitedforimplementationintothe
horndesign. Thethreaded13/8throatofthedriverprovideduswithaneasywaytomatethedriver
tothehornchannel,anengineeringdifficultywewerethankfullyabletobypass.
b.
Case
Design
Thedesignofthefoghornmustmeetcertaincriteria,themostimportantofwhichistheCoast
Guardspecificationforsoundpressurelevelatonemeter.Thisaudiblesignalwouldideallybeprojected
inahorizontalpattern,360degreesaroundthehorn.Thesecondcriterion,forcommercialpurposes,is
providingafoghornthatislightweightenoughtobeeasilytransportedbyhelicopterorsmallboatout
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totheinstallationsite. Thefoghorndriversandelectronicsmustbeprotectedfromtheelementsand
thehornitselfmustbeweatherproofandresistanttosaltwater.
WheninspectingthestructureofaBogennauticalloudspeaker,theteamnoticedthatthesound
traveledinthreedifferentdirectionsbeforeleavingthespeaker.Theloudspeakeritselfhadthree
differentsections,eachshapinganddirectingtheaudiblesignal. Inthefirstsection,thesoundtravels
fromthedriverupthroughatunedchannel.Inthesecond,acapencirclingtheinitialtubeprojects
soundbackdownandaroundtheinitialtube.Thelastsectionfeaturesanothercap,whichdirectsand
projectsthesoundbackupwardandout.Thisparticulardesignofferedamethodbywhichthedrivers,
orsourceofthesound,couldbeisolatedfromdirectexposuretotheenvironment.
Indesigningtheactualhorn,theteamwentthroughseveraldifferentapproaches.Theinitial
designswereunnecessarilycomplex,inthattheydemandedthreedifferentpartstobemadeinconical
shapes
and
were
of
extremely
precise
dimensions.
In
most
of
these
suggested
designs,
there
were
only
threepartsthatwereacousticallyessential:theinnerhorn,thecapandthewaveguide.Initially,allthree
weredesignedinconicalshape,withthewaveguideatasignificantangle.Thewaveguidewasdesigned
astwopiecessothatitcouldbeclaspedonthehornwhileallowingforaccesstothedrivers. Thisdesign
requiredaprecisefittotheinnerhorn whosewidthvariedaccordingtoheight andtothebase. This
approachwasabandonedinthefinaldesign,aswasthecapwhichnowrestedataperpendicularangle
tothetop.
ThedesignsubmittedtoWatermarkhadonlytwocomplexparts.Duetothedifficultyof
fabricatingthese
parts,
Watermark
made
several
alterations
to
the
design,
which
they
felt
would
simplifyfabrication.
Thefinaldesignisdividedintofivesegments,eachwithspecificacousticandstructuralroles
withinthefoghorn.
Thehornchannel,asshowninAppendixDfigure1,servesasthebaseandcentralcolumnofthe
horn.Itsupportsbothdriversfromthethreadedinsertsonitssides.Thethreadedrodrunsvertically
throughitscenterandlocksintoplacewithbolts.Thetuningplugispositionedinsidethechannel
betweenthedrivers,withthetopedgeperpendiculartothedrivers.Theinnerhornisthreadedtothe
topofthechannel.
Theinnerhorn(AppendixDfigure2),isusedtodirectthesoundtothetopofthecapandmatch
theacousticimpedanceofthechanneltothecap.Intheprototype,italsosupportsthewaveguide.Itis
attachedtothechannelbythreadsatitsmouth.
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Thewaveguide(AppendixDfigure3),isusedtofurtherdirectsoundreflectedfromthecap.It
convertstheverticalsoundwaveswhichreflectfromthecap,tohorizontalonesthatpropagatefrom
thehorn.Itisweldedtotheinnerhorn.
Thecap(AppendixDfigure4)directsthesoundfromtheinnerhorntothewaveguide.Itis
suspendedfromthethreadedrodbybolts.Itslargetopsurfaceallowsforthemountingofsignal
beaconsonbuoyswherespaceislimited.Itslongsidesfurtherredirectsoundenergy,whileprotecting
thehornchannelfromencroachmentofwater.
Thetuningplug(AppendixDfigure5)isusedtoredirectthesoundofthetwodriversupthe
hornchannel.Itsmainpurposeistoavoidhavingthedriversdirectingsoundonlyintoeachother.Itis
placedinsidethehornchannelwithitstopedgeperpendiculartothedrivers.Thetuningplugismade
outofPVC.
The
prototype
was
made
completely
out
of
aluminum
with
the
exception
of
the
tuning
plug.
The
totalweightofthehornis59.2poundsanditis34.5high(excessbaris12)and20wide.
c.
Amplifier
Circuit
Design
Thefoghornpoweramplifiercircuitisamultifunctional,lowpowercircuitusedtodrivethetwo
60wattcompressiondrivers.Theprincipalconsiderationinthedesignoftheamplifierwasmaximum
efficiency,sincethefoghornwouldbeoperatedbybattery. Themoreefficienttheamplifiercircuit,the
lessoftenthesebatterieswouldneedtobereplaced.
Anelectromagneticdriverworksbyfeedingcurrentthroughitinaforwardorreversedirection
togetthediaphragmtomoveinthecorrespondingdirectionbyanamountproportionaltothecurrent
itself. Thelimitationourdesignteamfacedisthatasingle12voltDCbatteryonlyproducesapolarized
voltage.ThisledustotheideaofincorporatinganintegratedcircuitcalledanHbridgeintoourcircuit
design.TheHbridge,inabasicsense,worksbysensingaPWM(pulsewidthmodulation)inputwith
multipletransistors
to
enable
asequence
of
switching
to
take
place.
The
switching
pattern
determines
atwhattimesthecurrentflowisforwardorreversedattheoutputsoftheHbridge.Reversingthe
directionofcurrentflowallowstheamplifiertousetheentirerangeofmotionoftheloudspeaker
driver,overcomingthelimitationofthepolarizedbattery.Tocontrolthecircuit,ourteamdetermined
thatthebestmethodforproducingthePWMcontrolvoltagewastouseamicrocontroller.Throughthe
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utilizationoftheHbridgeandmicrocontrollerourteamwasabletodesignandfabricateaproperly
functioningcircuitthatmaximizestheoverallefficiencyofthefoghorn.
Referringtothecircuitschematic,(AppendixE)themicrocontroller(Q2)requiresasupply
voltageof5voltsDC.Toprovidethis,a5voltvoltageregulator(Q1)isused. CapacitorsC1,C2,C3,and
C4actascouplingcapacitorswhichkeepACnoiseoffoftheDCvoltagescomingoutofthebatteryand
voltageregulator.CapacitorsC5andC6areusedaspartofthebootstrapcircuitryoftheHbridge.This
featurespeedsuptheriseandfalltimesoftheoutputsignal.
ThemicrocontrollerisprogrammedtooutputaTTLsquarewavewitha20secondperiod,a10%
dutycycle,andaburstfrequencyof950Hz. Pin6ofthemicrocontrollerconnectstoswitchS1andis
heldlowduringnormalfoghornoperation.ClosingtheswitchS1assertsthispinhighandsignalsthe
microcontrollertoshutthecircuitdownfortwohours. Thisfeatureisincludedforthebenefitof
maintenance
personnel
who
may
be
working
in
the
vicinity
of
the
foghorn
without
the
benefit
of
hearingprotection. Themicrocontrollerwillthenautomaticallyresumenormaloperationafter2hours
haveelapsed.
d.
Microcontroller
Design
ThemicrocontrolleristhebrainoftheFogHorn.Itgeneratesthe950Hzsoundwave,shutsoff
theHBridgeduringidletimes,andimplementsthekillswitch.
Wechosean8bitmicrocontrollerfromFreescalefromtheHCS08familyofmicrocontrollers
units(MCUs).WechosetheFreescaleMC9S08QD4microcontrollerforitslowprice,highavailability,
andeasyprogrammability.Inparticular,theMC9S08QD4microcontrollercomeswithtimerfunctionality
andkeyboardinterruptsthatallowsustoimplementallofthefeaturesnecessarytobothsatisfythe
coastguardspecificationsandthebusinessrequirementsofWatermarkNavigationSystems.
WeprogrammedthemicrocontrollerusingtheCprogramminglanguage.Wealsomadeuseof
theheader
files
that
reference
particular
memory
address
locations.
These
header
files
are
freely
availablefromFreescale.SeeAppendixBforthefullcodelisting.
Thefirstfeatureofnoteistheconfigurabletimeroverflowinterrupt.Weconfiguredthis
overflowsuchthattheinterruptfunctionwouldexecuteatarateof950.5Hz.Withinthisinterrupt
functionwecouldtoggletheoutputfrom0Vto5Vonapinofthemicrocontroller.This0Vto5Vtoggling
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actedasthesquarewaveinputtotheHBridgecircuit,whichconvertedthissignaltoa12Vto12V
squarewave.
Thenextproblemwehadtosolvewasthe10%dutycycle;thatis,generatingatonefor2
seconds,quietfor18seconds.WeaccomplishedthisusingtheRTI(RealTimeInterrupt)configuredto
executeevery8ms.Thus,theRTIfunctionexecutes250timesforevery2seconds.Thisallowsusto
controlboththesignalgenerationalongwithcountingthenumberofminutesthattheFogHornshould
remaindeadafterthekillswitchhasbeenpressed.
Thekillswitchfunctionalityisimplementedusingthekeyboardinterrupt.Thiskeyboard
interruptfunctionistriggeredwhentheresarisingedge(0to5V)ontheinputpin.Withintheinterrupt
functionweimmediatelystopanycurrentlyplayingsoundandsetacountertoresumenormal
functionalityafter2hours.
The
MCU
we
chose
has
over
2K
of
extra
ROM
space
and
nearly
2K
of
extra
RAM
memory.
Plus
3
freepinsareavailableforadditionalinputsandoutputs.Thisallowsforadditionalexpansionbasedon
marketrequirements.
e.
Fog
Horn
Testing
Uponcompletionofthehornitselfandtheinstallationofthesignalamplifierandcompression
drivers,itbecamenecessarytoperformtestingonthefullyrealizedfoghornprototype. Toisolateour
testingfrom
outside
interference,
and
to
eliminate
any
nuisance
caused
by
our
fog
horn,
testing
was
performedintheUNHanechoicchamber,locatedbehindChaseOceanEngineering. Ourtestswould
consistofsoundpressurelevelmeasurementsatspecificpowerlevels,frequencies,andpositions
relativetothehorn. AdetailedlistoftheequipmentusedinthesetestscanbefoundinAppendixC.
Ourfirstgoalwastoadjustthepositionofcapsectionandtuningplugsoastoproducethe
maximumpossiblesoundoutput. ByadjustingthePAamplifiertomimictheoutputpowerofthesignal
amplifier,thetestcouldbeperformedcontinuouslyasadjustmentsweremadetotherelativelengthof
thehornchannelthedistancebetweenthetuningplugandcap. Similarly,wewereabletovarythe
frequencyintotheamplifierfromthewaveformgenerator. Thisallowedustozeroinontheideal
combinationofhornchanneldimensionandoperatingfrequency.
Thepurposeofthecap/waveguideapproachwastoproduceaconsistenthorizontalsoundwave
360aroundthefoghorn. However,ourtestingrevealedthatthesoundpressurelevelwasnot
consistentwithpositionrelativetothehorn. Thiswasverifiedbytakingthesoundlevelmeasurement
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in10incrementsrelativetothepositionoftheoriginalmeasurement,whilemaintainingaconstant1
meterdistancefromthehorn.
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VI. Results
Ourtestingrevealedthattheidealsetupforthefoghornoccurredwhentheedgeofthecap
sectionwas
approximately
9.0above
the
surface
of
the
waveguide
section,
and
the
signal
tone
was
tunedto950.5Hz. Thisproducedasoundpressurelevelof120dBat1meterforaninputpowerof
23.76Wattsduringthe2secondburstofsound,and0.13Wattsduringthe18secondidletime.
Belowarethemeasurementsoftheprototypefoghornmeasuredat1meterwithaSPLMeter
withanaccuracyof2dB:
Table1:Directivitytestoffoghornat1m
Degrees SPL(dB) Degrees SPL(dB) Degrees SPL(dB) Degrees SPL(dB)
0 120 90 120 180 118 270 120
10
119
100
117
190
118
280
12020 118 110 118 200 118 290 120
30 120 120 119 210 118 300 119
40 120 130 117 220 119 310 118
50 120 140 117 230 118 320 120
60 119 150 120 240 117 330 118
70 119 160 117 250 117 340 118
80 120 170 119 260 118 350 119
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Figure1
50
100
150
90
270
180 0
Measured Omni-directional SPL Output of Fog horn
vs. Coast Guard Specification
Degrees
from Center
SPL (dB)
Coast Guard Specified SPL (119.3 dB)
Measured Foghorn SPL
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Figure2
Testingtheoutputofthevoltageregulator,microprocessor,andHbridgeofourcircuitrevealed
thatthecircuitwasworkingasdesigned.Referringtotable2,onecanobservethatourfoghorns
quiescentpowerconsumptionis.2812wattswhilethehornisnottransmitting.Duringsignaling,the
foghornconsumes
of
23.76
watts
for
the
period
of
2seconds.
The
total
calculated
power
consumption
perhouris4.29KW/h.Testingrevealsthatduringbroadcast,theamplifierdraws23.76wattsfromthe
supplyanddelivers22.2wattsofpowertothedrivers.Thisrepresentsanoverallelectricalefficiency
ratingof93.4%.
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40-15
-12
-9
-6
-3
0
3
6
9
12
15
Time (S)
Amplitud
e(Volts)
Measured Operation Cycle of Foghorn Amplifier
Duration = 20s; Duty Cycle = 10%
Burst Frequency = 950 Hz
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Table2:Foghornpowerconsumption
Current(Amps) Voltage(Volts) PowerConsumed(Watts)
2sBurstPeriod 1.98 12 23.76
18sQuiescentPeriod 0.027 12 0.2812
Full20speriod 1.85 12 22.2
Efficiency=93.4%
TotalPowerConsumption=4.29kW/h
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VII. Conclusion
In this project we attempted to design, for commercial use, a viable fog warning signal. This
foghorn would be of a rugged, weatherproof design, would be light and low profile enough to permit
transportation in a helicopter or small boat, and would produce an audible signal meeting or exceeding
the standards of the US Coast Guard.
Our specific design approach attempted to produce such an audible signal in every direction
relative to the horn. We further endeavored to transmit this signal in a horizontal pattern that would
deliver the maximum amount of power to vessels traveling on the water. Furthermore, our design
attempts to protect and insulate the horn channel from the incursion of rainwater, while providing a
stable platform for signal beacons or other equipment which may need to share space on a marker
buoy.
The results of the omnidirectional testing reveals that though the horn does exceed the Coast
Guard specification in certain directions, it is not within specification for others. This shortcoming is
most likely a combination of factors involving the horn bell section. Unable to fabricate the steep taper
of the bell in aluminum, Watermark was forced to use a thinner material and beat the shape by
hand. A large weld running up the side of the bell changes the acoustic properties of the horn on that
side. Lastly, the waveguide, having been fused to the horn bell, is not perfectly centered with respect to
the horn channel. Though the precise effect of each of these factors is unknown, it can be assumed that
a molded approach to mass production of the fog horn would alleviate losses from these prototype
inconsistencies.
In terms of the horns resistance to weather, it was realized that particularly heavy rain driven
by strong winds could encroach into the horn channel. Though the installation of a drain plug in the
channel was discussed, it soon became apparent that even with this precaution moisture could
accumulate in the throats of the drivers. A far better approach would be to direct the driver throats
vertically down, rather than horizontally as our design has done. This would also reduce the physical
strain which the drivers place on the sides of the channel. An improved design may feature a curved
horn channel, permitting the driver to be oriented in this way.
Though the foghorn meets Coast Guard specifications, it was realized through testing that the
cap section was absorbing a great deal of sound energy before reflecting it to the waveguide. This may
have been a function of a distance between cap and waveguide which was much larger than we had
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anticipated. The original design kept this gap very small, but at some point in the fabrication process it
became impossibility. The cap reflection approach may still be feasible, but based on testing results the
team concluded that the flat shape of the prototypes cap and its distance from the waveguide cause
unnecessary losses to the signal strength.
One of the great successes of the project was the implementation of the amplifier circuit. With
the exception of some non-ideal crackling in the signal output, the tone produced by the circuit was
very clear. The microcontroller performed flawlessly. The modular and waterproof design of the circuit
allows it to be plug-and-play for a technician servicing the fog horn. We believe this design with a
mind to maintenance will be a key selling point for this fog horn when it finally goes to market.
Overall, the project was a success in that it provides a stable and easily modified framework for
the design of a commercial fog horn. Subsequent ideas and features which Watermark wishes to
implement into their product can be quickly and easily realized by using the prototype as a standard orplatform for their implementation.
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Appendix A: References
Baldwin,KennethC.;Ph.D.Personalinterview.27November2008.
Drake,Allen;
Ph.D.
Personal
interview.
9April
2009.
Goodwin,PaulW.Personalinterviews.November2008April2009.
Kolbrek,Bjrn."HornTheory:AnIntroduction,Part1"
audioXpress2008.14November2008
.
UnitedStates.CoastGuard.DepartmentofHomelandSecurity. Title33Navigationand
NavigableWaters67.1010:OperatingRequirements. Washington:CoastGuard,2008.
UnitedStates.CoastGuard.DepartmentofHomelandSecurity. Title33Navigationand
NavigableWaters67.1020:SoundSignalTests. Washington:CoastGuard,2008.
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Appendix B: Microcontroller Code
As discussed in section V-d (Microcontroller Design), the code is in the C programming language
and uses standard headers provided free of charge from Freescale.
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in.c Thursday, April
*******************************************************************FogHornOS
Filename: main.cAuthor: Wyatt O'DayContact: [email protected]: 1.4
Last Modified: April 22, 2009
Description: Generates a 950.5 Hz square wave, 10% duty cycle(on 2 secs off 18 secs) and has a kill switch.
Also, to reduce power consumption, the H-Bridgewill be switched off when the sound wave isn'tbeing generated.
******************************************************************/
nclude /* for EnableInterrupts macro */nclude "derivative.h" /* include peripheral declarations */
efine BKGD_DISABLED
efine MODE_PULSE_ON 0efine MODE_PULSE_OFF 1efine MODE_DEAD 2
latile byte CurrentMode;
the amount of time the fog horn remainsdead after the kill switch has been hitefine MAX_DEAD_MINUTES 120
efine CHUNKS_IN_2SEC 250
latile byte Minutes, PulseSeconds, PulseChunks;
id SetMode(byte mode)
//Stop and reset the timerTPMSC_CLKSx = 0x00;TPMSC_TOF = 0;
CurrentMode = mode;
Minutes = 0;PulseChunks = 0;PulseSeconds = 0;
if(mode != MODE_PULSE_ON){
// switch pin to lowPTAD_PTAD4 = 0;
// turn off the H-Bridge (5 V)PTAD_PTAD3 = 1;
return;}else{
// turn on the H-Bridge (0V)
PTAD_PTAD3 = 0;-1-
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in.c Thursday, April
}
// Select Bus clock and Start the timerTPMSC_CLKSx = 0x01;
oid main(void)
EnableInterrupts;
#ifdef BKGD_DISABLEDSOPT1_BKGDPE = 0;#endif
//Set bus divide to divide by 8 ( 8 MHz / 8 = 1 Mhz Bus freq)ICSC2_BDIV = 3;
// Output pin (for sound wave)PTAD_PTAD4 = 0;PTADD_PTADD4 = 1;
// Output pin (for H-Bridge enable/disable)PTAD_PTAD3 = 0;PTADD_PTADD3 = 1;
// KBI Set Up for SW1 (pin 2 PTAD_PTAD2)
PTAPE_PTAPE2 = 1; /* Enable Pullup for Keyboard pin */KBIPE_KBIPE2 =1; /* Enable Keyboard Pin */
KBISC_KBIE = 1; /* Enable Keyboard Interrupts */KBISC_KBACK = 1; /* Clear Pending Keyboard Interrupts */
/*To calculate frequency the interrupt is called:
Bus FreqFrequency = ------------------
TPMMOD * Prescaler
With the bus divide set to 8 (ICSC2_BDIV = 3), thebus freq = clock freq / 8 = 8 MHz / 8 = 1 Mhz
The prescaler is in the form of 2^N where N can be 0 to 7.(Setting TPMSC_PS = 7, means prescaler = 2^7 = 128)
Lastly the TPMMOD can be any number from 1 to 65535.
*/
// set for freq = 950.5 Hz
// timer_setupTPMMOD = 526;TPMSC_PS = 0; //Set Div 1 prescalerTPMSC_TOIE = 1; // Enable Timer Overflow Interrupt
SetMode(MODE_PULSE_ON);
//enable the RTI for 8ms intervals (see pg 66 of MC9S08QD4)SRTISC = 0b00010001;
-2-
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in.c Thursday, April
// please make sure that you never leave this functionfor(;;) { __RESET_WATCHDOG(); }
Keyboard interrupt subroutineterrupt VectorNumber_Vkeyboard1 void KBI_ISR(void)
// kill switch was pressedSetMode(MODE_DEAD);
// Clear Pending Keyboard InterruptsKBISC_KBACK = 1;
TIM1OVFL_ISR - ISR that provides the timebase.terrupt VectorNumber_Vtpm1ovf void TIM1OVFL_ISR(void)
// toggle PortPTAD_PTAD4 = ~PTAD_PTAD4;
// clear TOFTPMSC_TOF = 0;
Real time interrupt - executed every 8msid interrupt VectorNumber_Vrti RTI_ISR(void)
// clear RTIFSRTISC_RTIACK = 1;
if(++PulseChunks == CHUNKS_IN_2SEC){
PulseChunks = 0;PulseSeconds += 2;
if(CurrentMode == MODE_PULSE_ON)SetMode(MODE_PULSE_OFF);
else if(CurrentMode == MODE_DEAD){
if(PulseSeconds == 60){
PulseSeconds = 0;
if(++Minutes == MAX_DEAD_MINUTES){
// switch back to the live modeSetMode(MODE_PULSE_ON);
}}
}else if (PulseSeconds == 18) // currently in MODE_PULSE_OFF
SetMode(MODE_PULSE_ON);
}
-3-
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Appendix C: Test, Measurement, and
Diagnostic Equipment
Model Number Manufacturer Nomenclature Specification
4050D Power Designs DC Power Supply 0-40 V, 0-5 A
15 Fluke Handheld Multimeter 0-1000 VDC, 0-750 VAC, 0-10 A
45 Fluke Auto-ranging Multimeter 0-1000 VDC, 0-750 VAC, 0-10 A
3020 BK Precision Sweep/Function Generator 0.2 Hz 2.0 MHz
MPA-101 Radio Shack P.A. Amplifier 100W maximum power
33-2055 Radio Shack Digital Sound Level Meter 50-126 dB SPL
2 dB @ 114 dB
SK0404 SKMI Oscilloscope/Function Generator 40 MHz Scope, 5MHz Function
Generator
Table 3: Test, Measurement, and Diagnostic Equipment
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Appendix D: Case Schematics
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4.30
4.70
8.00
.15
15.65
1.35
.25
.6
5
.75
1.50
2.50
1.35
10.00
.15
.75
.49
5.00
Horn
channel
FogHorn
4/24/2009
Figure1
View:Wireframe
0
.200
SCALE
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4.3
0
4.6
0
.20
.20
.15
13.2
5
70.8
109.2
Inn
er
ho
rn
FogH
orn
4/24
/2009
Fig
ure2
View:Wirefr
ame
0.1
80
SCALE
SEEDETAIL
A
0.3
60
SCALE
A
DETAIL
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5.75
.15
20.00
7.50
8.50
.15
45.0
Waveguide
FogHorn
4/24/2009
Figure3
View:Wirefra
me
0
.150
SCALE
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18.38
.25
7
.50
.75
Cap
FogHorn
4/24/2009
Figure4
View:Wireframe
0.1
50
SCALE
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1.00
1.39
4.00
56.3
.25
3.25
.70
Tu
ning
plu
g
FogHorn
4/24/2009
Figure5
View:Wirefram
e
0
.500
SCALE
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Appendix E: Amplifier Circuit Layout
Fog Horn Power Circuit PCB Parts
ComponentReferenceDesignator Value Part Number Description
Resistor
R1
2.4K Ohms
+/-5%
Capacitor
C1 2200uF/16V Coupling Capacitor
C2 1uF/12V Coupling Capacitor
C3 10uF/16V Coupling Capacitor
C4 .1uF Coupling Capacitor
C5 10nF Bootstrap Capacitor
C6 10nF Bootstrap CapacitorIC
Q1 LM7805C Votage Regulator
Q2 MC9SO8QD4CPC Micro Controller
Q3 LMD 18200 H-Bridge
Terminals
T1 Positive 12 Volts
T2 GND
T3 5 Volts to Switch
T4 5 Volts From Switch When Closed
T5 Output to Driver
T6 Output to DriverOff Board Connections
Switch
S1 Push Button
Drivers
D1 38109-855
Heavy Duty 60 W Compression
Driver
D2 38109-855
Heavy Duty 60 W Compression
Driver
Power
Supply
12 Volt DC Battery
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T1
T2
T3
T4
HGFEDCBA
8
7
6
5
4
3
2
1
HGFEDCBA
FogHornPowerCircuit
DRAWN
By:
MarcOuellette
ISSUED
SIZE
DATE:
DWGNO
REV
11x8.5
4/21/2009
SHEET
1OF1
T5
T6
C1
C2
1
2 3
Volta
geR
egula
tor
LM7
805
Q1
+5V
+12V
GND
12VD
C
Pow
er
Supply
S1
+__ +
D1
D2
FreescaleMC9S08QD4
Q2
1234
5678
1
2
3
4
5
6
7
8
9
10
11
H-Brid
ge
LMD1
82
00
Q3
C5
C6
C3
C4
R1G
ND
ON
PCB
BOARD
OFFP
CB
BOARD
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Appendix F: Bill of Materials
Fog Horn Bill of Materials
Item# Descr iption Part Number Source Qty Cost Total1 Support Rod
PaulGoodwin
1
$1,873.00 $1,873.002 Cap 1
3 Horn Channel 1
4 Inner Horn 1
5 Wave Guide 1
6CompressionDriver ID6ODT 38109-855 2 $187.86 $375.72
10 Switch 164TZ Mouser 1 $0.11 $0.11
11Water ProofJunction Box Newmar PX-1 1 $12.99 $12.99
Subtotal $2,261.82
Printed Circuit BoardItem# Descr iption Part Number Source Qty Cost
CostExt.
1Resistor 2.4Kohms mouser 1 $0.14 $0.14
2Capacitor2200uF/16V SLPX223M035H4P3 mouser 1 $4.34 $0.55
3Capacitor1uF/12V 311-1253-6-ND Digi-Key 1 $9.26 $9.26
4Capacitor10uF/12V UWX1C100MCL1GB Mouser 1 $0.16 $0.16
5Capacitor.1uF/12V UWX1H0R1MCL1GB Mouser 1 $0.17 $0.17
5 Capacitor 10nF81DA103M025JC2DE3 Mouser 2 $2.54 $5.08
6 H-Bridge LMD18200 Digi-Key 1 $14.14 $14.14
7 Voltage Regulator LM7805 Digi-Key 1 $0.66 $0.66
8 Microcontroller MC9S08QD4CPC Freescale 1 $0.69 $0.69
9 Terminal Board 158-P02ELK508V11 Mouser 3 $3.98 $11.94
Subtotal $42.79Total FogHorn Cost $2,304.61
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Appendix G: Fog Signal Design Criteria
1. USCGapproval33CFR67.10(1/2mileand2mileoutput),for2secondONand18secondOFF
(seeCFR
sound
chart
for
frequencies
and
pressure),
2. Permanentlabelstating;dateofUSCGapproval,manufacturer,modelname,approvedrange,
powerinputtotheemitterrequiredtomeetapprovedoutput,andthepowerinputtothe
entireunitrequiredtomeetapprovedoutput,
3. Solarpowersupply relativelylowpowerconsumptionoperatingat12voltsDCasunitwill
includesolarpanelsand12Vbatterybank(sizedbasedonpowerinputrequirementsTBD),
lesspowerusedthebetter,
4.
Relativelylightweightandsizedtofitintoahelicopterforoffshoreservice.Manyunitsare
offshoreand
accessed
only
via
helicopter
such
that
size
and
weight
will
be
aselling
factor
over
unitswhichrequireaworkboatorsupplyvessel(actualdesignweight,etc.TBD),lighter/smaller
thebetter,
5. Waterprooforpermanentlysealedelectronicsforlonglifeinasaltwaterenvironment.Manyof
thecompetitorsunits,onceopened,seemtosufferfromcorrosionissuesafterinitialservice.
Perhapsamoduledesignwherebynoworkwouldoccurinthefield,butcomponentscouldbe
swappedoutandservicedonshoreoratthefactory,tougherthebetter,
6. Temporaryshutdowncircuitwithwaterproofswitchtoallowtechnicianstheabilityto
temporarilydisablethesignaltoperformworkonthestructure,however,thefogsignalwill
automaticallydefaulttoONstatusafteraperiodofXXminutesOFF(TBD),perhapsincludinga
lesspowerfulsignaltoprovidenoticethehornwillcommencenormaloperationin5minutes,
7. FieldtestabletocertifypowerinputsandoutputsuchthataNavaidTechniciancancheckthe
unit,inplace,andverifyoperationtoapprovedstandardsandcompleteMMS/USCG90day
reportingrequirements,
8.
Simpleoperationandconnectivitytoexistingpowersupply/solarinstallations.Ifanenduser
alreadyhasbatteriesandsolarpanelsavailable,oursolutionshouldsimplyreplacetheageingor
inoperativeFogSignal,
OTHERCONSIDERATIONS:
1.PossibleGSMCellPhone/Satelliteconnectivityforreportingcapability,
2.Possibleuserprogrammableforvarioussoundpatterns,
3.PossibleGPSsynch.timingcircuittosynchronizewithotherfogsignals,
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