Contents
1. Introduction .............................................................................................................................................. 2
1.1
Problem Statement ....................................................................................................................... 2
1.2 Market Research ................................................................................................................................. 3
1.2.1 Background Research................................................................................................................... 3
1.3 Market Analysis ................................................................................................................................... 4
1.4 Market Research Conclusions ............................................................................................................. 6
2. Product Requirements .............................................................................................................................. 6
2.1 Customer Requirements ..................................................................................................................... 6
2.2 Product Specification .......................................................................................................................... 7
2.2 Competitive Value Analysis ................................................................................................................. 7
2.2.1 Customers’ Essential Criteria ....................................................................................................... 8
2.2.2 Customer Weights for Criteria ..................................................................................................... 8
2.3 Competitors ........................................................................................................................................ 8
2.3.1 Competitive Value Analysis ........................................................................................................ 10
3. Design Approach ..................................................................................................................................... 11
3.1 System Architecture .......................................................................................................................... 11
3.1.1 AC/DC Converter ........................................................................................................................ 11
3.1.2 Microphone................................................................................................................................ 11
3.1.3 Band-Pass Filter.......................................................................................................................... 11
3.1.4 Pattern Recognition ................................................................................................................... 12
3.1.5 Voltage Comparator ................................................................................................................... 12
3.1.6 JK Flip-Flop ................................................................................................................................. 12
3.1.7 Vibration Motor ......................................................................................................................... 12
3.2 Module Description .......................................................................................................................... 13
3.2.1 External “Wall Wart” AC/DC Converter .................................................................................... 13
3.2.2 Microphone................................................................................................................................ 13
3.2.3 Band-pass Filter.......................................................................................................................... 14
3.2.4 Pattern Recognition ................................................................................................................... 15
3.2.5 Voltage Comparator ................................................................................................................... 16
3.2.7 JK Flip Flop.................................................................................................................................. 17
3.2.6 Vibration Motor ......................................................................................................................... 17
3.3 Design Product Changes ................................................................................................................... 18
3.3.1 The Microphone ......................................................................................................................... 18
3.3.2 Band-Pass Filter.......................................................................................................................... 18
3.3.3 Updated Block Diagram ............................................................................................................. 18
5. Cost Analysis ........................................................................................................................................... 18
5.1 Initial Investment .............................................................................................................................. 18
5.2 Return on Investment ....................................................................................................................... 19
6. Design Issues ........................................................................................................................................... 19
7. Failure and Hazard Analysis .................................................................................................................... 20
8. Conclusion ............................................................................................................................................... 20
1. Introduction
1.1 Problem Statement
There are approximately 278 million deaf of hearing impaired people worldwide. While they are
sleeping, what are the chances that they wake up during a fire by a flashing strobe light? 23%. Also, all
fire alarm systems for the deaf are very elaborate and require a full reinstall of a system and become
very expensive.
We have created a modular fire alarm system with a vibration device that will properly alert a
person while asleep. Our device will work with any current fire alarm system, and does not require a
new system to be installed in the home.
1.2 Market Research
The first step in designing our fire alarm system was researching our market. We did initial
research by searching online search engines and looking through databases for information on deaf
people and fire alarm systems. Once we had a basic understanding of who we would be marketing our
device to, we looked at prior art and currently existing products in this market. After studying the pros
and cons of each different device, we consulted an expert at the Worcester Fire Department for his
input on these devices.
1.2.1 Background Research
According to the World Health Organization, there are approximately 278 million people
worldwide who suffer from moderate to profound hearing loss in both ears1. Most fire alarms primarily
use loud beeps to alert people of the emergency. Many workplaces and schools also use bright strobe
lights in their fire alarm systems. Deaf people are unable to hear these alarms, but can see the strobe
lights. We decided to focus our device towards the home user. Specifically, we realized that the biggest
fault in the system currently in place is when a deaf person is at home sleeping and the fire alarm goes
off.
Our research showed that there are two main methods of alerting deaf people of a fire. The first
method is a strobe light attached to the fire alarm. The second method is a vibrator placed under the
pillow or mattress of the person’s bed. Special smoke detectors are installed that, in addition to the loud
beeps, contain wireless transmitters. These transmitters send a signal to a receiver unit placed near the
bed, which in turn activates the vibrator. There have also been experiments with using a very pungent
smell to awake deaf people who are asleep. Japanese researchers have investigated the effectiveness of
using smoke alarms that spray wasabi extract into the room when activated2. This method successfully
woke 13 of 14 test subjects within 2 minutes. However, no actual products on the market currently
employ this method of waking people.
The National Fire Protection Association (NFPA) released a smoke alarm study called “Waking
Effectiveness of Alarms for Adults Who are Hard of Hearing3,4.” This report investigated the usefulness
bed-shaker and pillow-shaker devices, as well as strobe lights in waking up people who are hard of
hearing. The report found that only 27% of the participants woke up to a strobe light intensity above the
minimum intensity required by fire code standards for sleeping areas. Bed-shaking devices, which utilize
a vibrator placed under the mattress, and pillow-shaking devices, which utilize a vibrator placed under
the pillow, successfully woke 80% to 83% of the participants.
Our next step in our research was to interview an expert in the field. We conducted a phone
interview with Michael McNamee, the District Chief of Health and Safety. He has been with the
Worcester Fire Department for 37 years. After explaining our product idea to him, he told us about
1
2
3
http://www.who.int/mediacentre/factsheets/fs300/en/
http://inventorspot.com/articles/wasabi_silent_fire_alarm_alerts__11514
http://firechief.com/leadership/public-education/firefighting_nfpa_releases_two/
http://www.nfpa.org/assets/files//PDF/Proceedings/Smoke_Alarm_Notification_of_Sleeping_People_Progress_R
eport-.pdf
4
some building fire codes and the NFPA codes. We asked him what current methods were employed to
awake deaf people. He said that most of the time people have smoke detectors with a strobe light in the
bedroom. We also asked him what he would expect in a device that wakes up sleeping deaf people in an
emergency fire situation. He told us that he would want a device that combined the visual alerts, such as
the strobe lights, with a tactile alert, such as a vibrator placed under the pillow or mattress. This way you
would have double coverage.
As Michael said, most smoke alarms today are regulated by the NFPA4. NFPA 72 requires strobes
to flash at 1 to 2 Hz with an intensity of 177 or 110 candela, depending on their position. A Temporal 3
(T3) smoke alarm pattern is three half-second repetitions of the same sound, separated by half-second
pauses, followed by a 1.5 second pause after the third repetition5. The code minimum sound level for
audible alarms is 75dB2, and the frequency of the tone is commonly 3,150Hz, sometimes varying from
3,100 to 3,200Hz.
1.3 Market Analysis
The next step in our market research was to analyze current devices in the market already. After
searching through online stores such as Assistech, Inc (http://azhearing.com) and Harris
Communications (http://harriscomm.com), we found several products that are commonly used today to
alert deaf people of a fire. Some, like the Gentex Smoke Detector shown6 in Figure 1, employ a bright
flashing LED in addition to the loud beeping sound. The strobe flashes at a brightness of 177 Candela 60
times per minute. The detector mounts on the wall and retails for about $130. It comes with a one year
warranty.
Figure 1: Gentex Smoke Detector with Strobe Light
Other devices7, such as the Silent Call “Shake-Up Smoke Detector and Bed Shaker,” as shown in
Figure 2, utilize a custom smoke detector that has a built-in transmitter. When smoke is detected, the
transmitter sends a signal to a receiver unit that is connected to a pillow vibrator. The whole package
costs about $270. No advanced installation is needed. The smoke detector is powered by 9V batteries
and the receiver and vibrator are plugged into the wall. Additional smoke detectors with transmitters
can be purchased for about $115. Individual transmitter units that are hardwired into the fire alarm
5
http://www.harriscomm.com/catalog/product_info.php?products_id=19771&hcCsid=1440f713047f7ad336ea987
5e1be5ceb
6
http://www.azhearing.com/cgi-bin/shopper.cgi?preadd=action&key=710CSW
7
http://www.azhearing.com/products/Silent-Call-Smoke-Detectors.htm
system by a licensed fire alarm company can be purchased for about $70, plus installation fee. The
transmitter also needs to be placed within 75 feet of the receiver. The transmitter is shown in Figure 3.
The smoke detectors come with a one year warranty, while the standalone transmitter, receiver, and
vibrator each come with a five year warranty.
Figure 2: Shake-Up Smoke Detector and Bed Shaker
Figure 3: Silent Call Fire Alarm Transmitter
For extra protection, Silent Call makes a model with a strobe light on the receiver, as shown in
Figure 4. When the alarm goes off, the strobe flashes, a red indicator light is lit, and the vibrator turns
on. This package retails for about $325. No advanced installation is needed.
Figure 4: Shake-Up Smoke Detector and Bed Shaker with Strobe
1.4 Market Research Conclusions
From our market research, we have identified a gap in the current systems employed to awake
deaf people in case of a fire. Strobe lighting, while fairly common, has been shown to be ineffective. Bed
or pillow vibrators have seen a much higher success rate. However, all vibrators on the market now are
expensive (costing upwards of $250), and require specialty smoke alarms to be installed.
We wanted to make a product that was cheap and easy to set up and use but still very effective.
Our product idea should be modular in the sense that it works with existing systems already in place and
adds a vibrating unit. Since strobe lighting is common in the rooms of deaf people, adding a strobe light
adds extra expense. A strobe light could be added in a more expensive model if desired.
Our product will consist of a small, portable receiver connected to a vibrator. The receiver can
be taken anywhere and plugged into the wall for power. It will detect when the fire alarms go off, and
activate the vibrator. Since the receiver works with existing fire alarms, the cost of the adding this
system to the home will be kept low.
2. Product Requirements
2.1 Customer Requirements
Our market research produced an outline of customer expectations for our modular smoke
detector. This gives us specific direction on what is most important to build into our product. The
following list of requirements was constructed from our gathered data from interview surveys and
market research:
1)
2)
3)
4)
5)
6)
7)
Affordable
Easy to install
Durable
Movable
White
Bullet-Proof upon operation
Small, non-intrusive
Our product is very straight forward and no real surprised were requested or even assumed by
our market research. We understand that our product is a simple device, but the most important idea
that was requested from the market place would be to make our design reliable. Our product cannot
fail, it can be overly sensitive, that is better than not working in an emergency situation. This will be one
of our main and most difficult goal is developing our device. This level of dependability is expected by
the customer, and from our research people expect the device to seem and look similar to a smoke
alarm itself. Current device on the market today follow this trend and from a home owners standpoint
this type of appearance would be widely accepted.
2.2 Product Specification
Through our market research and customer feedback we were able to product a list of
specification for our device:
• ON/OFF button
• AC power supply input
• Backup Battery
• Wall Mounts
• White in Color
• Blue LED power notification
• Self-test Option
• Small Size
• Microphone
• Noise filter
• Strong plastic casing
• Multiple DSPs for possible multiple signals
• DC to DC converter for Output Vibrator
The customer is looking for something small that can be easily hidden or that looks similar to a
common fire alarm. The device should be easily place able within a room and not be intrusive. There
must be a way to test the device as we commonly and legally do with all modern fire alarm systems. Life
of the device is also a great concern because the system battery shouldn’t need replacing very often.
Most importantly is that the device should work without fail or with very little possible.
The device itself will operator as a microphone receiver. Once a tone of around 3200 Hz (which
is common, but more testing is needed, with most fire alarms) the device will activate an attached
hardwired vibrator unit. The microphone will operate with a noise filter and digital signal processor to
determine signal frequencies and rhythms.
2.2 Competitive Value Analysis
In order for our product to be successful, it has to have some advantage over existing products.
If customers see no benefit to purchasing our product over that of another company’s, then our product
will fail. To ensure that our smoke alarm system is competitive in the marketplace, we performed
competitive value analysis to compare our system to competitors. We weighted each of the customers’
criteria and assigned points to each system on how well it met those criteria.
2.2.1 Customers’ Essential Criteria
Based on our market research and our interview with the Worcester Fire Department Chief, we
have created a set of criteria that customers expect from a smoke detection system for the deaf. We
broke each criterion into the categories of quality, convenience, and cost.
The quality category is a very important one in the safety device market. A safety device has to
be made with quality so it can be trusted to operate sufficiently. That is why we decided the most
important criterion is reliability. If the system does not work when it is needed, then not only is it a
waste of money, but people could get hurt. The next criterion
In the convenience category, we decided the customer criteria are ease of installation,
modularity, and portability. Ease of installation is defined as the difficulty level of setting up and
installing the device into your home. If it requires licensed professional installation, then the ease of
installation is difficult, but if it just requires being plugged into a wall outlet, then it is easy. Modularity is
defined as how well the device works with existing systems. If it requires new equipment to be installed,
then modularity is low, whereas if it works with preexisting systems, then modularity is high. Portability
is defined as how easy it is to move the device around the house. If it can simply be unplugged from one
room and plugged into another room, then portability is high, whereas if it requires more work to move
then portability is low.
2.2.2 Customer Weights for Criteria
Since some criteria are more important than others, we assigned different weights to each
criterion. We decided that reliability is by far the most important criterion. Again, if the device does not
work, then people could get hurt or die. The second most important is cost. If the system is too
expensive, then people might not be able to afford it or might be unwilling to make the investment.
Ease of installation is the third most important criterion. If the system is confusing or difficult to set up,
then it might be installed improperly. Modularity and portability rank last in our weighting system.
These are both closer to being considered added bonus features rather than essential requirements.





Reliability
Cost
Ease of installation
Modularity
Portability
50
30
10
5
5
2.3 Competitors
There are a few existing competitors in the market for smoke detectors for deaf people. The first
competing product is the Shake-up Smoke Detector with Bed Shaker and Wall Mount8. It is shown below
in Figure 1. It comes with a smoke detector with a built-in wireless transmitter, a receiver, and an
attached bed vibrator. Vibrating discs have been shown to be the most effective at awaking people, so
this scores high in reliability. The total package retails for about $270, plus about $120 for additional
smoke detectors with built-in transmitters, so it scores low in cost. The installation process entails
plugging the receiver into the wall outlet, placing the vibrator under the bed or pillow, and then putting
in the new smoke alarm. Since it doesn’t require professional installation, but is not as simple as
plugging into the wall, it receives an intermediate score in the ease of installation category. It only works
8
http://www.azhearing.com/cgi-bin/shopper.cgi?preadd=action&key=SCSHKUPV
with proprietary smoke alarms, so it receives a low score in modularity. It is somewhat portable, as the
receiver can be unplugged and moved around, but it has to be within range of the transmitting smoke
alarm, so it receives an intermediate score in the portability category.
Figure 1 – Shake-up Smoke Detector
Another competing product is the Gentex Strobe Smoke Alarm9, as show below in Figure 2. It
uses strobe lights, which is somewhat effective at waking people, so it receives an intermediate score in
reliability. It retails for about $130, so it also receives an intermediate score in cost. The detector must
be wall-mounted and hardwired in, which requires professional installation, so it receives a low score in
ease of installation. Since it does not work with other systems, it gets a low score in modularity. Since it
is not able to be moved, it also gets a low score in portability.
Figure 2 – Gentex Strobe Smoke Alarm
The last competing product is the Alertmaster AM-10010 and Audio Alarm Transmitter11, as
shown below in Figure 3. The Audio Alarm Transmitter is placed near a smoke alarm. Once it is
9
http://www.azhearing.com/cgi-bin/shopper.cgi?preadd=action&key=710CSW
http://www.lssproducts.com/product/4690/ameriphone-alerting
10
triggered, it sends a wireless signal to the Alertmaster receiver. The receiver flashes a connected lamp.
This is less effective than the strobe, so it receives a low score in reliability. The total package costs
about $130, yielding an intermediate score in cost. Since the receiver is just plugged into the wall and
the transmitter is simply placed near the alarm, this gets a high score in ease of installation and
portability. It works with existing smoke alarms, so it gets a high score in modularity.
Figure 3 – Alertmaster AM-100 and Audio Alarm Transmitter
Our design for our product tries to maximize its score in each customer requirement. It uses
vibration, the most effective technique at waking people, so it gets a high score in reliability. It does not
require any expensive components, so cost should be less than $50, netting a high score in cost. No
transmitter is involved, just simply the sensor is placed near the bed and the vibrator is placed under the
bed or pillow. This makes ease of installation very simple and gets a high score. It also makes it highly
portable, so it receives a high score in portability. Since it works with the existing fire alarms, it receives
a high score in modularity.
2.3.1 Competitive Value Analysis
Characteristics
Weight
Competitors
Shake-Up
Gentex Strobe
Alertmaster
WPI
11
Reliability Cost
50
30
3
2
1
3
1
2
2
3
Ease of
Installation
10
2
1
3
3
http://www.lssproducts.com/product/4694/ameriphone-alerting
Modularity Portability Total
5
5
1
1
3
3
2
1
2
3
215
180
165
300
3. Design Approach
3.1 System Architecture
3.1.1 AC/DC Converter
We chose to use an off the shelf AC to DC converter which both saves us time and space within
our main device housing. This is a simple “wall wart” in which the brick is self-contained and directly
touches the wall.
AC/DC Converter
Purpose
Implementation
Input
Output
Convert power from the standard US wall outlet to usable DC Power
Rectify/Bridge/Regulate AC wave from transformer signal
110V/220V AC
12V DC at 2.5A+ (Depending on Mode of Operation)
Table
This module involves no construction on our part and will provide the base 12V source which
will be stepped down for most of our electronics. It largest current load by far will be the vibration
motor, which will be rarely in operation.
3.1.2 Microphone
The first module in our block diagram is an electret microphone that will accept a unique signal
from a fire alarm system. Our microphone can accept frequencies that our alarm system outputs,
between 3000 and 3200 Hertz.
Microphone
Purpose
Implementation
Input
Accept output from fire alarm system and output a voltage
Using a voltage divider, our DC bias will be 2.5 volts
1.14 mA at 2.5V
Table
The microphone is very important in our design because it accurately has to accept its inputs.
The output voltage from our microphone will be passed through a band-pass filter and a voltage
comparator to determine if both the frequency and decibel level correspond with a fire alarm system.
3.1.3 Band-Pass Filter
The purpose of the band pass filter is to filter out random noise and sound outside the range of
3000-3200Hz. This frequency range is the pitch of a fire alarm. The filter will be implemented using
hardware. A second-order active filter consisting of an op-amp, capacitors, and resistors is enough to
make an analog filter. Software implementation using an analog-to-digital converter and a
microcontroller is certainly possible; however, it is more expensive. Since the filter is cheap and
relatively easy to build in an analog circuit, we chose the hardware implementation.
3.1.4 Pattern Recognition
Our pattern recognition system utilizes an envelope circuit and uses a shift register to hold the
values from the JK Flip-Flop, and if the correct pattern is determined in will trigger the output on. This is
an optional addiction to our product and only requires powering the shift register which we have room
for in our supply’s wattage range.
Pattern Recognition
Implementation
Input
Output
Status
Recognizes a pattern through sampling at 2Hz
Filter signal from active filter
Trigger Power to Vibration motor through MOSFET
Complete
Table
3.1.5 Voltage Comparator
Our voltage comparator will be an LM358 operational amplifier that will accept the output
voltage from our band-pass filter. The purpose of the comparator will be to determine if the input signal
decibel level is within range of the fire alarm (85 dB).
Voltage Comparator
Purpose
Implementation
Input
To determine if the decibel level is within the range of a fire alarm
Using an operational amplifier, we will set reference levels and if
the output is above, the decibel level is corrent.
Output of the band-pass filter
Table
Without the voltage comparator, any frequency level between 3000 and 3200 Hz would set off
our vibration device. This would cause for many faults in our safety device, and is unacceptable.
3.1.6 JK Flip-Flop
The purpose of the band pass filter is to ensure that once a fire alarm is detected, the motor
turns on and stays on regardless of input. This way, the motor will not just vibrate when the fire alarm is
beeping, and will continuously vibrate once the alarm is detected. It will only stop vibrating when the
reset button is pressed.
3.1.7 Vibration Motor
To wake the occupants during an emergency situation that exists during a fire alarm we need to
produce a strong vibration. To do this we chose a 25mm off weight vibration motor that has more than
enough strength to do the job.
Vibration Motor
Purpose
Wake the sleeping occupant
Implementation
Input
Constant Vibration produced from off centered counterweight
85mA at 5V DC
Table
The motor itself has a self-contained free-wheeling diode, and the only necessary construction
besides running leads to will be to self-contain this motor in its own housing. This housing will be made
of solid plastic and will be able to endure a considerable amount of abuse. Our only concern is
producing enough vibration and making the device itself attractive relatively speaking.
3.2 Module Description
3.2.1 External “Wall Wart” AC/DC Converter
Our main choose is an external supply by the Emerson cooperation which produces a 12V
12Watt adapter that would be perfect for our needs. Considering the availability of external AC to DC
converters and there relatively low cost we are gaining two advantages. Those being the time saved in
not designing our own converter and, the cost and space of placing one inside the device itself. For
future designs we may look to implement a completely battery operated system but that has
considerable draw backs especially in the size and type of vibration motor that can be use to alert the
occupants. Also through our market research most products do use an external converter and
customers on the vanity side don’t seem to mind its look and design. Overall since we would need to
run a cord to the system anyway, containing a small brink near the base of the cord is just common
sense.
External AC/DC Converter
Input Voltage/Current
Input Frequency
EMI/RFI
Output Voltage
Maximum Power
Voltage Regulation
0.25 A rms @ 120 Vac
47-63 Hz
FCC Part 15, Subpart B Class B & EN55022 (CISPR
22) Class B
5-12V
12W for 12V
± 5% @ constant voltage mode
Table
3.2.2 Microphone
When searching for our microphone, there were a few things that we had to focus on. We had
to make sure that our device worked within a reasonable operating range, operated in a specific
frequency range, used wire leads, and was omni-directional. Lastly, we were concerned with the cost of
the microphone due to our budget. The figure below shows the important parts of our electrets
microphone.
Electret Microphone
Voltage Rating
2 – 10 Volts
Current
Frequency
Impedance
Termination
Direction
500 uA
100 Hz – 20 kHz
2200 Ohms
Wire Leads
Omni-directional
Table
We are implementing our electret microphone by setting up a voltage divider where the
microphone is represented by the resistance value R2 (2200 Ohms). The microphone will pull a current
of 500 uA while operating at a voltage of 3.67 Volts. The resistance values were given a 5% tolerance
rate like the ones from out lab kits. Our output voltage from the microphone will be biased, and a
coupling capacitor. The figure below shows our model with its readings in MultiSim.
Figure
3.2.3 Band-pass Filter
The filter will provide a gain of 50-65 to any frequencies between 3000-3200Hz. Outside of that
frequency range, it will provide a gain of 0. Shown below in Figure X is the simulated frequency response
of our test circuit in Multisim.
Figure 2
Equation X.0 is the equation for the center frequency of a high-Q active band-pass filter configured as
shown in Figure X.
1
𝑓𝑜 =
Equation 1
𝑅 𝑅
2𝜋𝐶√( 1 2 )𝑅3
𝑅1 +𝑅2
The equation for the bandwidth of this filter is shown below in Equation X.0.
𝐵=
1
𝜋𝐶𝑅3
Equation 2
Plugging in values of R1 = 1kΩ, R2 = 17Ω, R3 = 15.9kΩ, and C = 0.1uF yields fo = 3100Hz and B =
200Hz. In our current working circuit we are using more standard component values as well as models of
real op-amps. We are testing R1 = R2 = 10Ω, R3 = 51kΩ, and C = 0.1uF. The simulated frequency
response is shown below in Figure X.0. Note that this output is from a first-order active filter, not a
second-order one.
3.2.4 Pattern Recognition
The purpose of the envelope circuit is to produce a more stable input to our voltage comparator
and to help recognize a T3 signal pattern from the microphone. The envelope circuit averages the noise
or constant gain and drop of the input signal and produces a smoother curve. Based on our interface
with the clock and sampling with the JK Flip-Flop we can recognize a specific pattern in time from our
microphone.
Figure
3.2.5 Voltage Comparator
The main points in our operational amplifier when used in our comparator is its operating
voltages/currents, a general purpose amplifier, and its package type. Also, we were concerned with the
cost. Since we are using the amplifier as a comparator it did not necessarily have to have high gain.
Category
Integrated Circuits (ICs)
Family
Amplifiers - Instrumentation, OP Amps, Buffer Amps
Series
-
Amplifier Type
General Purpose
Number of Circuits
2 - Dual
Package / Case
8-DIP
Slew Rate
0.6 V/µs
Gain Bandwidth Product
1MHz
Current - Supply
1.5mA
Current - Output / Channel
40mA
Voltage - Supply, Single/Dual (±) 3 V ~ 32 V, ±1.5 V ~ 16 V
Current - Input Bias
45nA
Operating Temperature
0°C ~ 70°C
Voltage - Input Offset
2000µV
Table
We will implement our voltage comparator right after the band-pass filter. The output voltage of
the band-pass filter will be proportional to the decibel level of the input sound. The operational
amplifier will have reference voltages that will compare the input to the comparator with each
reference. If the input is greater, the output will swing high meaning the fire alarm has been initialized. If
it is lower, then there is no output.
3.2.7 JK Flip Flop
3.2.6 Vibration Motor
The motor itself will be tied directly to the input DC rail of the 12V source. To turn on the motor
we will be using a 2N3904 BJT which will be connected to the JK flip-flop. The circuit below outlines the
interconnection between devices and its power supply. Physically the motor just requires a constant DC
voltage to operate or spin. The spinning off-weight produces it vibrations and based on its size and
weight we have estimated that it provide enough vibration to wake the occupant.
Vibration Motor
Size/Weight
Operating Voltage/Current
Off-Center Weight
24.4mm 25.4g
12VDC @ 220mA
10g
Table 8
Figure
3.3 Design Product Changes
As we continued forward with our design, there were a couple of changes that we had to
consider because we ran into some errors. The two errors that we found with our design were our bandpass filter and our microphone. We were able to fix one of the issues, and remain confident that our
other issue can be easily fixed.
3.3.1 The Microphone
We have found that our microphone does not have a very large radius when trying to pick up
the signal from our fire alarm. Although the specific microphone that we plan on purchasing is not very
expensive in bulk, we have not implemented it into our current system. The microphone is a very
important part of our design, however it is not essential at this point that we move forward with
purchasing a new one.
3.3.2 Band-Pass Filter
Our filter was very sensitive in that it would accept a variety of noises and then turn on our
vibration device. Also, our filter was oscillating without an input, so it was clear that we were going to
have to re-design our filter. We met with Professor Bitar to determine what was wrong with our filter
design, and determined that we needed to alter some resistance and capacitance values. We then
changed the values by a factor of 10, and our filter worked exactly how we needed it to.
3.3.3 Updated Block Diagram
Input Signal
3-3.3 kHz
T3 Standard
Band Pass
Filter
Voltage
Comparator
Shift
Register
Vibration
Motor
Power
Transistor
JK Flip
Flop
Logic
Circuit
5. Cost Analysis
5.1 Initial Investment
Our initial investment is set at $500,000, and this might appear to be very high. However, there is a high
startup fee for our product, but once it gets going, there is very little maintenance. We plan on selling
our product through an online website that we will develop and implement. This way we will not have to
sell our item to anyone, just product it and worry about the functionality of our product. Also, we have
to pay to create the assembly line for our product. However, once we have the base set down, we will
have to make sure the assembly line is running correctly, as well as update our website.
5.2 Return on Investment
•
Fixed Cost: $500,000
•
Unit Cost: $22.00 at 100,000 units
•
Total Production Cost: $2.7 million
•
Selling Price: $65.00
•
Total Revenue: $6.5 million
•
Profit: $3.8 million
•
Return on Investment:
We plan on starting our business with only 100,000 units at $22.00 to produce and package. We will be
able to sell our product for only $65.00, which is much lower than any competition. If all items are sold,
we will have revenue of $6.5 million, and a production cost of $2.7 million. That means that’s we will
have a profit of $3.8 million after the production of only 100,000 devices.
6. Design Issues
Overall our design was successful and from our testing reasonable reliable. If we did have more
time to develop our project or improve on the current design we would have certainly done so,
especially with additional features, as long as they don’t offset our cost greatly.
The first feature we were hoping to implement was a Battery backup system with three AAA
common batteries. Our main design to implement that functionality would be to utilize a bilateral
analog switch with a comparator. The low power comparator itself would powered by the batteries at
an extremely low current drain (~5uA). This comparator would detect when the DC power supply fails
and then trigger the bilateral analog switch, which is powered by the battery and run our device. If
possible we could charge the batteries, while the main DC supply is on, to keep them at their optimum
backup time. To signal the user that the device is operating off the battery we will have an indication
LED mounted on the outside of the chasse.
The biggest risk that we don’t want to make is producing or adding features that make our
device much to expense. The attractiveness of our device from our interaction with the market has
been our production price. That was why our design strategy of going completely analog allowed our
price point to be so low, but on the downside is limited our future ease of implementation of features.
The functionality of our prototype was able to meet all primary requirements from our
customers. The device is able to receive from any sound source from at most a range of 10 feet
(currently) and only if that sound is between 3k-3.2kHz and with a T3 specific pattern will trigger our
output the vibrator.
To conform that our designed worked we performed iterative testing as we build our product.
For example we tested our filter and comparator together against a number of frequencies generated
sounds and sounds from our microphone to perform two tasks. One was to make sure our modules
were working correctly and second to create correct bias voltages to trigger the comparator itself high.
This design approach allowed us to make strides and know exactly where we were on our development,
knowing what was finished and what needed to be done.
When completed we were able to successfully test our device at several distances. At a
distance of five feet we were required to increase the sensitivity simply by decreasing our reference bias
voltages of the comparator.
Overall as a safety device our product is very reliable even though that could be improved by
making adjustments to our filter of our biasing points. As is our product is functional and reasonable for
the length of time given for development and build time given.
7. Failure and Hazard Analysis
There are two defined failure zone with our product that we recongized. First of all since our
product relys on sampling at specific intervals, we can misinterpret logical beeps and therefore our
vibration motor will not trigger. The motor not going of is a large hazard for the user and therefore may
result in injury or possible death. We are currently looking at possible redundent systems.
The second hazard area is the sound source not turning on or not producing enough sound to
trigger the device. This is usually something we cannot control, but we have done some work with
amplification, but that does sometimes result in false positives. The most common problem of these
two hazards was the device not sampling correctly and not triggering. A false alarm is better than none
at all in a emergency situation.
Possible hazards we found were electrical shock if something is spilt on the vibrator. We were
able to overcome this with a much more sealed case. Secondly the possiblity of faults occuring and
cutting power to the device is something to consider. This could be remedied with a simple battery
backup which we have designed but not implemented.
8. Conclusion
Our product is a fire alarm for the deaf and hearing impaired, targeted specifically for home use. It
works by producing powerful vibrations to wake the user. Vibration alert systems are already in
existence, but they cost well over $300 and are more difficult to install. Our system saves cost by
utilizing existing fire alarm detection systems, saving the manufacturer money on hardware and the user
money on installation.
Our target market is the deaf and hearing impaired. The product will be sold through specialty websites
and catalogs. It can get recommended through physicians and through deaf organizations, such as the
Hearing Loss Association of America. We contacted presidents of local chapters of the HLAA, and they
were very excited to hear about our product. Some requested samples to showcase at their monthly
chapter meetings, and we also got invited to the HLAA National Conference in Nashville, TN to
demonstrate our product.
The main advantages of our product are its low cost, modularity, and reliability. It can be sold at retail
for less than half the cost of existing systems and still make a sizeable profit. It works with existing fire
alarm systems in the home, so nothing has to be replaced, saving the user time and money. It produces
powerful vibrations strong enough to wake up any user, making it very reliable.