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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: wyattoday@gmail.comRevision: 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,