Fog Horn University of New Hampshire 

Undergraduate Ocean Research Project 2008‐2009  

4/26/2009     

Team Members: Mathieu Feraud Dan Fournier Wyatt O'Day Marc Ouellette 

 

Advisors: Kenneth Baldwin, Ph.D. 

Alan Drake, Ph.D.  

 

 

 

 

 

Table of contents 

Sections  

Acknowledgments          Page 3 

I. Abstract            Page 4 

II. Introduction            Page 5 

III. Background            Page 6 

IV. Methods            Page 7 

V. Discussion            Page 9 

  a. Drivers          Page 9 

b. Case Design          Page 9 

c. Amplifier Circuit Design      Page 11 

d. Microcontroller Design      Page 12 

e. Fog Horn Testing        Page 13 

VI. Results            Page 15 

VII. Conclusion            Page 19 

Appendices   

A. References            Page 21 

B. Microcontroller Code         Page 22 

C. Test, Measurement, and Diagnostic Equipment  Page 26 

D. Case Schematics          Page 27 

E. Amplifier Circuit Layout        Page 33 

F. Bill of Materials          Page 35 

G. Fog Signal Design Criteria        Page 36 

Acknowledgements This work is the result of research sponsored in part, by the National Sea Grant College Program, 

NOAA, Department of Commerce, under grant #NA06OAR4170109 through the New Hampshire Sea 

Grant College Program. 

The fog horn design team would like to acknowledge the following persons and entities, whose 

contributions and guidance made the successful completion of the project possible. 

 

Kenneth Baldwin, Ph.D. 

Alan Drake, Ph.D. 

Jennifer Bedsole 

Paul Goodwin 

Watermark Navigation Systems, 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   Warning signals have been used for centuries as a method for warning nautical vessels of the 

presence of hazards and obstacles in open water.  Such signals become necessary when visibility 

conditions are such that a warning beacon cannot be seen in time for the ship to change course.  Thus, 

the nautical warning signal‐‐ or foghorn, as it is more commonly known‐‐ is an invaluable tool for 

navigation.   The prevalence of off‐shore oil platforms makes the modern foghorn especially important 

to modern seafarers.  

  Watermark Navigation Systems, LLC is the manufacturer and distributor of a wide range of 

nautical aids, including marker buoys and signal beacons.  Watermark found that a common complaint 

amongst their customer base was the lack of an inexpensive, lightweight, and low‐maintenance foghorn.  

Seeing this opportunity to meet a market need while expanding their product base, Watermark 

approached the University of New Hampshire with the proposal to sponsor an undergraduate project 

team in the design of such a foghorn.    

  Though it is relatively simple in concept, a viable foghorn presents unique challenges to a team 

of engineers.  One must consider the environment in which the horn is to operate.  The foghorn will 

constantly be exposed to moisture and salt from seawater.  It must be able to withstand wind and heavy 

rains as well as a wide range of temperatures.  It must be small and light enough to make transportation 

out to its installation site economically viable.  In contrast, it must be rugged enough to remain 

unaffected by a harsh outdoor environment.  Most importantly, it must produce a signal which is 

audible to a vessel at distances far enough to avoid the obstacle.  The production of such a powerful 

audible signal carries with it its own engineering challenges in terms of the power required to produce 

it. 

  Thus, the aim of this project team was to approach this unique and very real engineering 

challenge and devise a foghorn which would meet the specified criteria and serve as the prototype for 

Watermark’s own line of foghorns.   The team consisted of a small, interdisciplinary group of engineers 

who saw in this project the opportunity not only to innovate but to also gain the experience of having 

guided an idea through the stages of design to emerge with a marketable product. 

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III. Background   When Paul Goodwin of Watermark proposed the foghorn project to the University, he included 

in the project description several features that he expected the final foghorn to possess.   Obviously, the 

design constraints mentioned earlier were mentioned.  These specific design goals can be seen in 

Appendix G:  “Fog Signal Design Criteria”.  

Principal among these constraints was the production of an audible signal of specific duration 

and loud enough and to meet the Coast Guard specification.  The primary criteria of this specification 

are that the signal must be approximately 120 decibels at 1 meter and that it persists for 2 seconds over 

a 20 second interval. 

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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 drivers

made the most sense.

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V. Discussion   After choosing the compression drivers as the method to make sound, we then began breaking 

the problem of making a working fog horn prototype into approachable pieces. 

a. Compression Drivers  

  A wide array of loudspeakers are commercially available, and thus it became necessary to 

“narrow the field” for drivers which would be appropriate to the fog horn application.  The first criterion 

which the driver had to meet was the ability to provide at least the specified sound pressure level given 

a reasonable power signal.   Secondly, the driver must operate well within the region of the horn’s signal 

frequency.  According to the Coast Guard specification, this includes tones as low as 400 Hz and as high 

as 1.2 kHz.   A criterion which became apparent after attempting to order several drivers was the actual 

commercial availability of the driver itself.   Some drivers were discovered which could meet the 

demands of our horn, but which turned out to be manufactured by a company that had gone out of 

business or had ceased carrying the product. 

  The drivers on which the design team eventually settled were the Electro Voice® ID60DT heavy‐

duty compression drivers.  These high power industrial drivers featured a ruggedized design, a sealed 

wiring compartment, tropicalized metal parts for resistance to humidity, and weatherproof paint.  The 

ready availability and its weather‐resistant features made it ideally suited for implementation into the 

horn design.  The threaded 1 3/8” throat of the driver provided us with an easy way to mate the driver 

to the horn channel, an engineering difficulty we were thankfully able to bypass. 

b. Case Design  

  The design of the fog horn must meet certain criteria, the most important of which is the Coast 

Guard specification for sound pressure level at one meter. This audible signal would ideally be projected 

in a horizontal pattern, 360 degrees around the horn. The second criterion, for commercial purposes, is 

providing a fog horn that is lightweight enough to be easily transported by helicopter or small boat out 

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to the installation site.  The fog horn drivers and electronics must be protected from the elements and 

the horn itself must be weatherproof and resistant to salt water.  

  When inspecting the structure of a Bogen nautical loudspeaker, the team noticed that the sound 

traveled in three different directions before leaving the speaker. The loudspeaker itself had three 

different sections, each shaping and directing the audible signal.  In the first section, the sound travels 

from the driver up through a tuned channel. In the second, a cap encircling the initial tube projects 

sound back down and around the initial tube. The last section features another cap, which directs and 

projects the sound back upward and out. This particular design offered a method by which the drivers, 

or source of the sound, could be isolated from direct exposure to the environment. 

  In designing the actual horn, the team went through several different approaches. The initial 

designs were unnecessarily complex, in that they demanded three different parts to be made in conical 

shapes and were of extremely precise dimensions. In most of these suggested designs, there were only 

three parts that were acoustically essential: the inner horn, the cap and the waveguide. Initially, all three 

were designed in conical shape, with the wave guide at a significant angle. The wave guide was designed 

as two pieces so that it could be clasped on the horn while allowing for access to the drivers.  This design 

required a precise fit to the inner horn‐‐ whose width varied according to height‐‐ and to the base.  This 

approach was abandoned in the final design, as was the cap which now rested at a perpendicular angle 

to the top. 

  The design submitted to Watermark had only two complex parts. Due to the difficulty of 

fabricating these parts, Watermark made several alterations to the design, which they felt would 

simplify fabrication. 

  The final design is divided into five segments, each with specific acoustic and structural roles 

within the fog horn.  

  The horn channel, as shown in Appendix D figure 1, serves as the base and central column of the 

horn. It supports both drivers from the threaded inserts on its sides. The threaded rod runs vertically 

through its center and locks into place with bolts. The tuning plug is positioned inside the channel 

between the drivers, with the top edge perpendicular to the drivers. The inner horn is threaded to the 

top of the channel.  

  The inner horn (Appendix D figure 2), is used to direct the sound to the top of the cap and match 

the acoustic impedance of the channel to the cap. In the prototype, it also supports the wave guide. It is 

attached to the channel by threads at its mouth.  

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  The wave guide (Appendix D figure 3), is used to further direct sound reflected from the cap. It 

converts the vertical sound waves which reflect from the cap, to horizontal ones that propagate from 

the horn. It is welded to the inner horn. 

  The cap (Appendix D figure 4) directs the sound from the inner horn to the wave guide. It is 

suspended from the threaded rod by bolts. Its large top surface allows for the mounting of signal 

beacons on buoys where space is limited. Its long sides further redirect sound energy, while protecting 

the horn channel from encroachment of water. 

  The tuning plug (Appendix D figure 5) is used to redirect the sound of the two drivers up the 

horn channel. Its main purpose is to avoid having the drivers directing sound only into each other. It is 

placed inside the horn channel with its top edge perpendicular to the drivers. The tuning plug is made 

out of PVC. 

The prototype was made completely out of ¼” aluminum with the exception of the tuning plug. The 

total weight of the horn is 59.2 pounds and it is 34.5” high (excess bar is 12”) and 20” wide. 

 

c. Amplifier Circuit Design  

  The fog horn power amplifier circuit is a multifunctional, low power circuit used to drive the two 

60‐watt compression drivers. The principal consideration in the design of the amplifier was maximum 

efficiency, since the fog horn would be operated by battery.  The more efficient the amplifier circuit, the 

less often these batteries would need to be replaced.    

  An electromagnetic driver works by feeding current through it in a forward or reverse direction 

to get the diaphragm to move in the corresponding direction by an amount proportional to the current 

itself.  The limitation our design team faced is that a single 12‐volt DC battery only produces a polarized 

voltage. This led us to the idea of incorporating an integrated circuit called an H‐bridge into our circuit 

design. The H‐bridge, in a basic sense, works by sensing a PWM (pulse‐width modulation) input with 

multiple transistors to enable a sequence of switching to take place. The switching pattern determines 

at what times the current flow is forward or reversed at the outputs of the H‐bridge. Reversing the 

direction of current flow allows the amplifier to use the entire range of motion of the loudspeaker 

driver, overcoming the limitation of the polarized battery. To control the circuit, our team determined 

that the best method for producing the PWM control voltage was to use a microcontroller. Through the 

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utilization of the H‐bridge and microcontroller our team was able to design and fabricate a properly 

functioning circuit that maximizes the overall efficiency of the foghorn.    

  Referring to the circuit schematic, (Appendix E) the microcontroller (Q2) requires a supply 

voltage of 5 volts DC. To provide this, a 5 volt voltage regulator (Q1) is used.  Capacitors C1, C2, C3, and 

C4 act as coupling capacitors which keep AC noise off of the DC voltages coming out of the battery and 

voltage regulator. Capacitors C5 and C6 are used as part of the bootstrap circuitry of the H‐bridge. This 

feature speeds up the rise and fall times of the output signal.  

The microcontroller is programmed to output a TTL square wave with a 20 second period, a 10% 

duty cycle, and a burst frequency of 950 Hz.  Pin 6 of the microcontroller connects to switch S1 and is 

held low during normal fog horn operation. Closing the switch S1 asserts this pin high and signals the 

microcontroller to shut the circuit down for two hours.  This feature is included for the benefit of 

maintenance personnel who may be working in the vicinity of the foghorn without the benefit of 

hearing protection.  The microcontroller will then automatically resume normal operation after 2 hours 

have elapsed. 

 

d. Microcontroller Design  

  The microcontroller is the brain of the Fog Horn. It generates the 950Hz sound wave, shuts off 

the H‐Bridge during idle times, and implements the kill switch. 

We chose an 8‐bit microcontroller from Freescale – from the HCS08 family of microcontrollers 

units (MCUs). We chose the Freescale MC9S08QD4 microcontroller for its low‐price, high availability, 

and easy programmability. In particular, the MC9S08QD4 microcontroller comes with timer functionality 

and keyboard interrupts that allows us to implement all of the features necessary to both satisfy the 

coast guard specifications and the business requirements of Watermark Navigation Systems. 

We programmed the microcontroller using the C programming language. We also made use of 

the header files that reference particular memory address locations. These header files are freely 

available from Freescale. See Appendix B for the full code listing. 

The first feature of note is the configurable timer overflow interrupt. We configured this 

overflow such that the interrupt function would execute at a rate of 950.5 Hz. Within this interrupt 

function we could toggle the output from 0V to 5V on a pin of the microcontroller. This 0V to 5V toggling 

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acted as the square wave input to the H‐Bridge circuit, which converted this signal to a ‐12V to 12V 

square wave. 

The next problem we had to solve was the 10% duty cycle; that is, generating a tone for 2 

seconds, quiet for 18 seconds. We accomplished this using the RTI (Real‐Time Interrupt) configured to 

execute every 8ms. Thus, the RTI function executes 250 times for every 2 seconds. This allows us to 

control both the signal generation along with counting the number of minutes that the Fog Horn should 

remain dead after the kill switch has been pressed. 

The kill switch functionality is implemented using the keyboard interrupt. This keyboard 

interrupt function is triggered when there’s a rising edge (0 to 5V) on the input pin. Within the interrupt 

function we immediately stop any currently playing sound and set a counter to resume normal 

functionality after 2 hours. 

The MCU we chose has over 2K of extra ROM space and nearly 2K of extra RAM memory. Plus 3 

free pins are available for additional inputs and outputs. This allows for additional expansion based on 

market requirements. 

e. Fog Horn Testing  

  Upon completion of the horn itself and the installation of the signal amplifier and compression 

drivers, it became necessary to perform testing on the fully realized fog horn prototype.   To isolate our 

testing from outside interference, and to eliminate any nuisance caused by our fog horn, testing was 

performed in the UNH anechoic chamber, located behind Chase Ocean Engineering.  Our tests would 

consist of sound pressure level measurements at specific power levels, frequencies, and positions 

relative to the horn.  A detailed list of the equipment used in these tests can be found in Appendix C.

  Our first goal was to adjust the position of cap section and tuning plug so as to produce the 

maximum possible sound output.  By adjusting the PA amplifier to mimic the output power of the signal 

amplifier, the test could be performed continuously as adjustments were made to the relative length of 

the horn channel – the distance between the tuning plug and cap.  Similarly, we were able to vary the 

frequency into the amplifier from the waveform generator.  This allowed us to “zero in” on the ideal 

combination of horn channel dimension and operating frequency.   

  The purpose of the cap/waveguide approach was to produce a consistent horizontal sound wave 

360° around the fog horn.  However, our testing revealed that the sound pressure level was not 

consistent with position relative to the horn.  This was verified by taking the sound level measurement 

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in 10° increments relative to the position of the original measurement, while maintaining a constant 1 

meter distance from the horn.    

14

VI. Results   Our testing revealed that the ideal setup for the foghorn occurred when the edge of the cap 

section was approximately 9.0“above the surface of the waveguide section, and the signal tone was 

tuned to 950.5 Hz.  This produced a sound pressure level of 120 dB at 1 meter for an input power of 

23.76 Watts during the 2 second burst of sound, and 0.13 Watts during the 18 second idle time.    

Below are the measurements of the prototype fog horn measured at 1meter with a SPL Meter 

with an accuracy of ±2 dB: 

Table 1: Directivity test of fog horn at 1m 

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°  120 20°  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 

 

 

 

 

 

 

 

 

 

 

 

 

15

Figure 1 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

16

Figure 2 

 

 

  Testing the output of the voltage regulator, microprocessor, and H‐bridge of our circuit revealed 

that the circuit was working as designed. Referring to table 2, one can observe that our fog horn’s 

quiescent power consumption is .2812 watts while the horn is not transmitting. During signaling, the 

foghorn consumes of 23.76 watts for the period of 2 seconds. The total calculated power consumption 

per hour is 4.29KW/h. Testing reveals that during broadcast, the amplifier draws 23.76 watts from the 

supply and delivers 22.2 watts of power to the drivers. This represents an overall electrical efficiency 

rating of 93.4%. 

 

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)

Am

plitu

de (

Vol

ts)

Measured Operation Cycle of Foghorn AmplifierDuration = 20s; Duty Cycle = 10%

Burst Frequency = 950 Hz

17

Table 2: Fog horn power consumption 

  Current (Amps)  Voltage (Volts)  Power Consumed (Watts) 

2s Burst Period  1.98 12 23.76 18s Quiescent Period   0.027 12 0.2812 Full 20s period  1.85 12 22.2 

 

Efficiency = 93.4% 

Total Power Consumption = 4.29 kW/h 

18

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 ¼” 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 horn’s 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

19

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 prototype’s 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 or

platform for their implementation.

20

Appendix A:  References Baldwin, Kenneth C.; Ph.D. Personal interview. 27 November 2008. 

Drake, Allen; Ph.D. Personal interview. 9 April 2009. 

Goodwin, Paul W. Personal interviews. November 2008 – April 2009. 

Kolbrek, Bjørn. "Horn Theory: An Introduction, Part 1" audioXpress 2008. 14 November 2008 <http://www.audioxpress.com/magsdirx/ax/addenda/media/kolbrek2884.pdf>.  

United States. Coast Guard. Department of Homeland Security.  Title 33‐‐Navigation and 

Navigable Waters § 67.10‐10: Operating Requirements.  Washington: Coast Guard, 2008. 

United States. Coast Guard. Department of Homeland Security.  Title 33‐‐Navigation and 

Navigable Waters § 67.10‐20: Sound Signal Tests.  Washington: Coast Guard, 2008. 

 

21

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.

22

main.c Thursday, April 23, 2009

/********************************************************************* FogHornOS*** Filename: main.c* Author: Wyatt O'Day* Contact: wyattoday@gmail.com* Revision: 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-Bridge* will be switched off when the sound wave isn't* being generated.*********************************************************************/

#include <hidef.h> /* for EnableInterrupts macro */#include "derivative.h" /* include peripheral declarations */

#define BKGD_DISABLED

#define MODE_PULSE_ON 0#define MODE_PULSE_OFF 1#define MODE_DEAD 2

volatile byte CurrentMode;

// the amount of time the fog horn remains // dead after the kill switch has been hit#define MAX_DEAD_MINUTES 120

#define CHUNKS_IN_2SEC 250

volatile byte Minutes, PulseSeconds, PulseChunks;

void 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-

23

main.c Thursday, April 23, 2009

}

// Select Bus clock and Start the timerTPMSC_CLKSx = 0x01;

}

void 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 Freq Frequency = ------------------ TPMMOD * Prescaler

With the bus divide set to 8 (ICSC2_BDIV = 3), the bus 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 prescaler TPMSC_TOIE = 1; // Enable Timer Overflow Interrupt

SetMode(MODE_PULSE_ON);

//enable the RTI for 8ms intervals (see pg 66 of MC9S08QD4)SRTISC = 0b00010001;

-2-

24

main.c Thursday, April 23, 2009

// please make sure that you never leave this functionfor(;;) { __RESET_WATCHDOG(); }

}

// Keyboard interrupt subroutineinterrupt 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.interrupt VectorNumber_Vtpm1ovf void TIM1OVFL_ISR(void){

// toggle PortPTAD_PTAD4 = ~PTAD_PTAD4;

// clear TOFTPMSC_TOF = 0;

}

// Real time interrupt - executed every 8msvoid 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-

25

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

26

Appendix D:  Case Schematics 

27

4.30

4.70

8.00

.15

15.65

1.35

.25.65

.75

1.50

2.50

1.35

10.00

.15

.75

.49

5.00

Horn channel

Fog H

orn4/24/2009

Figure 1

View

: Wirefram

e

0.200S

CA

LE

28

4.304.60

.20

.20

.15

13.25

70.8°

109.2°

Inner horn

Fog H

orn4/24/2009

Figure 2

View

: Wirefram

e

0.180S

CA

LE

SE

E D

ET

AIL

A

0.360S

CA

LE

AD

ET

AIL

29

5.75

.15

20.007.50

8.50

.15

45.0°

Wave guide

Fog H

orn4/24/2009

Figure 3

View

: Wirefram

e

0.150S

CA

LE

30

18.38

.25

7.50

.75

Cap

Fog H

orn4/24/2009

Figure 4

View

: Wirefram

e

0.150S

CA

LE

31

1.001.39

4.00

56.3°

.25

3.25

.70

Tuning

plug

Fog H

orn4/24/2009

Figure 5

View

: Wirefram

e

0.500S

CA

LE

32

Appendix E: Amplifier Circuit Layout Fog Horn Power Circuit PCB Parts

Component Reference Designator 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 Capacitor IC 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 Driver

Off 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

33

T1

T2T3

T4

HGFEDCBA

87

65

43

21

HGFEDCBA

87

65

43

21

Fog H

orn P

ow

er Circuit

DR

AW

N

By:

Marc O

uellette

ISS

UE

D

SIZ

ED

AT

E:

DW

G N

OR

EV

11x8

.54

/21/2009

SH

EE

T1

OF

1

T5

T6

C1

C2

1

2 3

Vo

ltag

e Re

gu

lator

LM

7805Q

1+

5V

+12V

GN

D

12V D

CP

ow

erS

up

ply

S1

+__ +

D1

D2

Freescale MC9S08QD4

Q2

1234

56781

2

3

4

5

6

7

8

9

10

11

H-B

ridg

eL

MD

18200

Q3

C5

C6

C3C4

R1GN

D

ON

PC

BB

OA

RD

OF

F P

CB

BO

AR

D

34

Appendix F:  Bill of Materials 

Fog Horn Bill of Materials Item # Description Part Number Source Qty Cost Total 1 Support Rod

Paul Goodwin

1

$1,873.00 $1,873.002 Cap 13 Horn Channel 14 Inner Horn 15 Wave Guide 1

6 Compression Driver ID6ODT 38109-855 2 $187.86 $375.72

10 Switch 164TZ Mouser 1 $0.11 $0.11

11 Water Proof Junction Box Newmar PX-1 1 $12.99 $12.99

Subtotal $2,261.82

Printed Circuit Board Item # Description Part Number Source Qty Cost

Cost Ext.

1 Resistor 2.4K ohms mouser 1 $0.14 $0.14

2 Capacitor 2200uF/16V SLPX223M035H4P3 mouser 1 $4.34 $0.55

3 Capacitor 1uF/12V 311-1253-6-ND Digi-Key 1 $9.26 $9.26

4 Capacitor 10uF/12V UWX1C100MCL1GB Mouser 1 $0.16 $0.16

5 Capacitor .1uF/12V UWX1H0R1MCL1GB Mouser 1 $0.17 $0.17

5 Capacitor 10nF 81DA103M025JC2DE3 Mouser 2 $2.54 $5.08

6 H-Bridge LMD18200 Digi-Key 1 $14.14 $14.147 Voltage Regulator LM7805 Digi-Key 1 $0.66 $0.668 Microcontroller MC9S08QD4CPC Freescale 1 $0.69 $0.699 Terminal Board 158-P02ELK508V11 Mouser 3 $3.98 $11.94 Subtotal $42.79

Total Fog Horn Cost $2,304.61

 

35

Appendix G:  Fog Signal Design Criteria  

1. USCG approval – 33 CFR 67.10 (1/2 mile and 2 mile output), for 2 second ON and 18 second OFF (see CFR sound chart for frequencies and pressure), 

 2. Permanent label stating; date of USCG approval, manufacturer, model name, approved range, 

power input to the emitter required to meet approved output, and the power input to the entire unit required to meet approved output, 

 3. Solar power supply ‐ relatively low power consumption operating at 12 volts DC as unit will 

include solar panels and 12V battery bank (sized based on power input requirements – TBD), less power used the better, 

 4. Relatively light‐weight and sized to fit into a helicopter for offshore service. Many units are 

offshore and accessed only via helicopter such that size and weight will be a selling factor over units which require a workboat or supply vessel (actual design weight, etc. TBD), lighter/smaller the better, 

 5. Waterproof or permanently sealed electronics for long‐life in a saltwater environment. Many of 

the competitors units, once opened, seem to suffer from corrosion issues after initial service. Perhaps a “module” design whereby no work would occur in‐the‐field, but components could be swapped out and serviced on‐shore or at the factory, tougher the better, 

 6. Temporary shut‐down circuit with waterproof switch to allow technicians the ability to 

temporarily disable the signal to perform work on the structure, however, the fog signal will automatically default to ON status after a period of XX minutes OFF (TBD), perhaps including a less powerful signal to provide notice the horn will commence normal operation in 5 minutes, 

 7. Field testable to certify power inputs and output such that a Navaid Technician can check the 

unit, in place, and verify operation to approved standards and complete MMS/USCG 90 day reporting requirements, 

 8. Simple operation and connectivity to existing power supply/solar installations. If an end user 

already has batteries and solar panels available, our solution should simply replace the ageing or inoperative Fog Signal, 

 OTHER CONSIDERATIONS:  1. Possible GSM Cell Phone/Satellite connectivity for reporting capability, 2. Possible user‐programmable for various sound patterns, 3. Possible GPS synch. timing circuit to synchronize with other fog signals, 

36