PULSE OXIMETER
DISPLAY SYSTEM
Final Report
Taylor DeHaan, Scott Block, Nick McKee
ENGR 339 Senior Design Project, Calvin College
© 2015, Taylor DeHaan, Scott Block, Nick McKee and Calvin College
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1
Executive Summary
The PODS (Pulse Oximeter Display System) wrist pulse oximeter reduces the risk of pilots succumbing
to hypoxia while flying at high altitude. The problem with current pulse oximeters is that they are bulky
and are worn on the finger, discouraging pilots from wearing them during entire flights. PODS’s pulse
oximeter and warning system seeks to passively monitor a pilot’s oxygen level through reflectance
oximetry and actively warn them when they are in danger of not having enough oxygen in their body.
PODS’s is comprised of four Electrical and Computer Engineers and created a pulse oximeter prototype
and business plan to deliver this highly marketable and valuable product. Given the current market value
for pulse oximeters stands at $1.6 billion yearly and the size of the pilot market is over 600,000 people, it
will take about 3,265 units at $500 each to be a profitable company in its first year. This equates to
roughly 0.1% of the pulse oximeter market and 0.5% of pilots. These data plus the success in prototyping
has lead PODS to determine that this product is marketable and feasible.
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Table of Contents
1
Executive Summary .............................................................................................................................. 2
2
Introduction ........................................................................................................................................... 7
3
2.1
Project Description........................................................................................................................ 7
2.2
Need for Solution .......................................................................................................................... 7
Project management .............................................................................................................................. 8
3.1
Team organization ........................................................................................................................ 8
3.1.1
Team members ...................................................................................................................... 8
3.1.2
Advisors ................................................................................................................................ 8
3.2
Budget ........................................................................................................................................... 9
3.3
Work Hours................................................................................................................................... 9
3.4
Method of Approach ................................................................................................................... 10
3.4.1
Research method ................................................................................................................. 10
3.4.2
Team communication method ............................................................................................. 10
3.4.3
Design Method .................................................................................................................... 10
3.4.4
Testing Method ................................................................................................................... 10
4
Currently Marketed Device Research ................................................................................................. 11
5
Requirements ...................................................................................................................................... 11
5.1
Design Schedule.......................................................................................................................... 13
5.2
System Architecture .................................................................................................................... 14
5.2.1
Probe ................................................................................................................................... 15
5.2.2
Amplifier and Filter ............................................................................................................ 15
5.2.3
Analog to Digital Converter ................................................................................................ 15
5.2.4
Digital to Analog Converters .............................................................................................. 15
5.2.5
Microprocessor.................................................................................................................... 16
5.2.6
Display Driver ..................................................................................................................... 16
5.2.7
Display ................................................................................................................................ 16
5.2.8
Speaker ................................................................................................................................ 16
5.2.9
Software .............................................................................................................................. 16
5.3
Design Norms ............................................................................................................................. 18
5.4
Design Components .................................................................................................................... 19
5.4.1
Physical Device (Probe) ...................................................................................................... 19
5.4.2
Oximetry ............................................................................................................................. 21
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5.4.3
Light Source and Sensor Network ...................................................................................... 22
5.4.4
Display System ................................................................................................................... 23
5.4.5
Hardware/Display System Interface ................................................................................... 24
5.4.6
Microprocessor.................................................................................................................... 26
5.4.7
Filtering ............................................................................................................................... 28
5.4.8
Analog Signal Conversion .................................................................................................. 29
5.4.9
Digital Signal Conversion ................................................................................................... 31
5.4.10
Graphic User Interface (GUI) ............................................................................................. 32
5.5
6
7
8
Integration, Test, and Debug ....................................................................................................... 33
Operations ........................................................................................................................................... 35
6.1
Legal form of Ownership ............................................................................................................ 35
6.2
Company structure ...................................................................................................................... 35
6.3
Decision making authority .......................................................................................................... 36
6.4
Significant compensation and benefits packages ........................................................................ 36
Industry Profile and Overview ............................................................................................................ 36
7.1
Industry background and overview ............................................................................................. 36
7.2
Major Customer Groups.............................................................................................................. 36
7.2.1
Aviation............................................................................................................................... 36
7.2.2
Military ............................................................................................................................... 36
7.2.3
Medical ............................................................................................................................... 37
7.2.4
Emergency Response Units ................................................................................................ 37
Business Plan ...................................................................................................................................... 37
8.1
SWOT Analysis .......................................................................................................................... 37
8.1.1
Strengths ............................................................................................................................. 37
8.1.2
Weaknesses ......................................................................................................................... 37
8.1.3
Opportunities....................................................................................................................... 37
8.1.4
Threats................................................................................................................................. 37
8.2
Marketing Strategy...................................................................................................................... 38
8.2.1
Demographics ..................................................................................................................... 38
8.2.2
Customers' motivation to buy ............................................................................................. 38
8.2.3
Market size and trends ........................................................................................................ 38
8.2.4
Advertising and promotion ................................................................................................. 38
8.3
Competitive Analysis .................................................................................................................. 39
4
8.3.1
Existing Competitors........................................................................................................... 39
8.3.2
Potential Competitors .......................................................................................................... 40
8.4
8.4.1
Development Costs ............................................................................................................. 40
8.4.2
Fixed Costs.......................................................................................................................... 41
8.4.3
Variable Costs ..................................................................................................................... 42
8.5
9
Cost Estimate .............................................................................................................................. 40
Feasibility.................................................................................................................................... 42
8.5.1
Income Statement ................................................................................................................ 43
8.5.2
Balance Sheet ...................................................................................................................... 43
8.5.3
Cash Flow Statement .......................................................................................................... 43
8.5.4
Break-even Analysis ........................................................................................................... 43
8.5.5
Ratio Analysis ..................................................................................................................... 43
Prototypes ........................................................................................................................................... 43
9.1
Transmittance Oximetry Prototype ............................................................................................. 43
9.2
Reflectance Oximetry Prototype ................................................................................................. 44
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Deliverables .................................................................................................................................... 45
10.1
Transmittance Oximeter Prototype ............................................................................................. 45
10.2
Reflectance Oximeter Prototype ................................................................................................. 45
10.3
Oximeter Circuit Design ............................................................................................................. 45
10.4
Oximeter Software ...................................................................................................................... 48
10.5
Graphic User Interface ................................................................................................................ 48
10.6
Product Concept Design.............................................................................................................. 48
11
Future work ..................................................................................................................................... 49
12
Conclusion ...................................................................................................................................... 49
13
Acknowledgements ......................................................................................................................... 50
14
References ....................................................................................................................................... 51
15
Appendix 1: Maxim MAX1416 Data Sheet.................................................................................... 52
5
Table of Figures
Figure 1. Level 1 Block Diagram................................................................................................................ 14
Figure 2. Hardware/Software Interface Block Diagram ............................................................................. 17
Figure 3. Company Structure ...................................................................................................................... 36
Figure 4. Transmittance Prototype .............................................................................................................. 44
Figure 5. Reflectance Oximeter Prototype .................................................................................................. 45
Figure 6. Oximetry Circuit .......................................................................................................................... 46
Figure 7. Oximetry Gerber file ................................................................................................................... 47
Figure 8. Circuit Prototype ......................................................................................................................... 48
Figure 9. Final Product Concept ................................................................................................................. 49
Table of Tables
Table 1. Work Hours..................................................................................................................................... 9
Table 2. Design Hours Breakdown ............................................................................................................... 9
Table 3. Market Devices ............................................................................................................................. 11
Table 4. Fall Work Breakdown Schedule ................................................................................................... 13
Table 5. Spring Work Breakdown Schedule ............................................................................................... 14
Table 6. Finger Device Decision Matrix ..................................................................................................... 20
Table 7. Prototype Housing Decision Matrix ............................................................................................. 21
Table 8. Oximetry Decision Matrix ............................................................................................................ 22
Table 9. Display Decision Matrix ............................................................................................................... 24
Table 10. Bluetooth/WiFi/ZigBee Comparison Summary.......................................................................... 25
Table 11. Hardware/Display System Interface Decision Matrix ................................................................ 26
Table 12. Microprocessor Decision Matrix ................................................................................................ 27
Table 13. Filter Decision Matrix ................................................................................................................. 28
Table 14. Analog to Digital Converter Decision Matrix............................................................................. 29
Table 15. Analog to Digital Converter Decision Matrix............................................................................. 30
Table 16. Digital to Analog Converter Decision Matrix............................................................................. 31
Table 17. GUI Decision Matrix .................................................................................................................. 32
Table 18. Integration, Test, and Debug List ............................................................................................... 33
Table 19. Development Cost....................................................................................................................... 41
Table 20. Fixed Cost ................................................................................................................................... 42
Table 21. Variable Cost .............................................................................................................................. 42
Table 22. Income Sheet............................................................................................................................... 53
Table 23. Statement of Cash Flow .............................................................................................................. 53
Table 24. Break Even Analysis ................................................................................................................... 54
Table 25. Ratio Analysis ............................................................................................................................. 56
Table 26. Budget ......................................................................................................................................... 57
Table 27. Work Hours Breakdown ............................................................................................................. 58
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2 Introduction
2.1 Project Description
The Pulse Oximeter Display System (PODS) team’s project solves the problem of hypoxia negatively
impacting people’s lives. Hypoxia is a condition resulting from low oxygen in a person’s blood and
affects a variety of people including pilots in unpressurized airplanes flying above 10,000 feet and people
with medical conditions such as chronic obstructive pulmonary disease (COPD). This project remedies
this problem through pulse oximeter monitoring and displaying someone’s oxygen level and issuing a
warning if they are in danger of becoming hypoxic. This device is analogous to using a breathalyzer to
check blood alcohol levels. A few design constraints include: designing the oximeter to be comfortably
worn for hours at a time; not interfere with someone’s range of motion or use of hands; the system
displaying the oxygen levels, pulse, etc. must be able to be easily seen and decipherable; and provide
visual and auditory warnings when oxygen levels get too low. If a pilot were to use this device, he should
have complete freedom to use his hands, easily keep an eye on his oxygen level, and trust the system to
warn him when he is in danger of hypoxia.
2.2 Need for Solution
Hypoxia is a broad medical condition where the amount of oxygen in the body reaches a critical level.
The critical level for the average person’s blood oxygen level is about 90%. Below 90%, a person starts
experiencing symptoms of nausea, dizziness, headache, difficulty breathing, coughing, weakness,
disorientation, and lethargy. It can affect a variety of people such as divers using a closed loop rebreather,
people with certain medical conditions, or mountaineers, so PODS decided focused on pilots because of
the recreational implications. For recreational activities, people broadly try to reduce the risk of that
activity and pilots are no different. The risks associated with flying include technological failures, weather
hazards, among many others. There is one risk, however, that pilots easily overlook and that is hypoxia.
The FAA states that pilots flying above 10,000 feet must be on some form of oxygen, but this regulation
fails to account for two crucial factors: the exact altitude when hypoxia begins to onset in a pilot; and if a
pilot is getting sufficient oxygen through their oxygen supply. Low oxygen levels at high altitude affect
each person differently based on a variety of factors, including fitness level and tobacco use, putting some
at risk of becoming hypoxic before 10,000 feet. It stands to reason that pilots should have access to a
device that measures the level of oxygen in their blood. Furthermore, this device must be comfortable to
wear and not inhibit a pilot’s dexterity in any way. Finally, this device should clearly issue a warning
when a pilot is in a potentially dangerous situation.
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3 Project management
3.1 Team organization
The team consists of three senior engineers in the electrical and computer concentration. The project is
divided into separate tasks and each member of the group is in charge of a different part of the project.
3.1.1 Team members
Nick McKee: Nick is an electrical/computer engineering concentration from Arlington Heights, Illinois.
He has also been a four-year member of the Calvin College Cross Country team and also of the Calvin
College Track and Field Team. He has experience working as a controls engineer intern. He has been
assigned the task of researching business components of the project and creating the Graphic User
Interface.
Taylor DeHaan: Taylor is a senior electrical/computer engineering student from Excelsior, Minnesota.
Taylor has interned for Seagate Technology in Bloomington, Minnesota over the summer of 2013 and
again in Longmont, Colorado over the summer of 2014. He is currently continuing his work from the past
summer in a part-time intern position and has accepted a permanent role in the Advanced Storage
Development team at Seagate starting the summer of 2015. Taylor’s role in team consists of lead
research, system design, software/hardware development, and team webmaster.
Scott Block: Scott is an electrical/computer engineering concentration student from Grand Rapids,
Michigan. The past 8 years of his life have been spent serving in the military with two overseas tours to
Iraq and Afghanistan. As a software engineering intern, Scott worked at Visteon Corporation during the
summer of 2014 developing quality control and quality assurance tools in python for the infotainment in a
Mazda 3. Scott led the team in reflectance oximetry research, sensor component selection, software filter
design and testing.
3.1.2 Advisors
The team’s main advisor is Professor Mark Michmerhuizen. He received his BSE from Calvin College
and went on to obtain his MSEE from the University of Michigan and his MBA from Grand Valley State
University. He worked in industry for 22 years before joining the staff at Calvin College. Professor
Michmerhuizen mainly aided the team by giving feedback on design ideas and by giving professional
advice.
The team was also in contact with Taylor’s father, Doug DeHaan, a private pilot and avid aviation
enthusiast. He originally proposed the project idea to the team after seeing a tangible need for the device
in private aviation. Throughout the year, he has provided specifications and possible features for the
device and has provided input from other pilots on the project.
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3.2 Budget
The team was allotted a budget of $500 dollars for prototyping and other peripherals to the project. The
team has procured two Raspberry Pis and its necessary accessories (i.e. memory card, break out wires,
and power supply), a high resolution analog to digital converter, 2 digital to analog converters, LEDs,
Photodiodes, 3D printed housings, and photodiodes. The accrued amount spent on these components is
$165.69 leaving $334.31 left in the team budget. A budget breakdown can be seen in the Appendix
section.
3.3 Work Hours
The table below is an estimate of the number of hours that team members put into the project. These
numbers are estimates that are within ±20% of their true values. A more detailed breakdown of hours
spent on each piece of the project can be seen in the Appendix section.
Table 1. Work Hours
Approximate Total Person
161.25
Scott
253.75
Taylor
158.33
Nick
573.33
Total
The table below shows the approximate number of hours that the team put into each of the design
components. These values are estimated to be within ±20% of their true values.
Table 2. Design Hours Breakdown
Item
Hours
Hardware
70
Software
250
GUI
60
Housing
10
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3.4 Method of Approach
3.4.1 Research method
The research for this project was done using various online and journal sources. Other universities and
colleges have published papers tackling a similar device and approaching it in different ways. This
research yielded ideas for solutions and testing.
3.4.2 Team communication method
The teams’ main form of communication is through weekly meetings where the plan for each week is set.
Current and future obstacles were also discussed during this time with the goal of ensuring that each team
member was up to date on the project.
3.4.3 Design Method
3.4.3.1
Stage One
The team researched the pulse oximetry industry and compared the current products available to
consumers. This research includes looking into design alternatives. This is also when the selection of
which components to use for the different aspects of the project takes place.
3.4.3.2
Stage Two
The team focused on getting all the individual components of the project working. This involves building
a bench top transmittance oximeter prototype. This prototype showed that all of the components worked
together. This stage is a transitional stage between one and three.
3.4.3.3
Stage Three
The team transitioned the bench top prototype of a transmittance oximeter into a reflectance model. The
team developed a housing unit and went through iterations or design improvement. The team developed a
graphic user interface and warning system. This stage is a transitional stage between three and four.
3.4.3.4
Stage Four
The team integrated the different aspects of the bench top prototype, housing unit, graphic user interface,
and warning system into one working model. This model and along with this report were the final
deliverables for the project.
3.4.4 Testing Method
PODS employed an iterative testing method. The approach was to establish a goal and break it into
smaller sub-tasks. Each subtask was researched and a solution was designed, implemented, and tested. If
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the solution implemented is successfully tested, then the next task is started. If the solution implemented
doesn’t solve the problem, then the process is repeated.
4 Currently Marketed Device Research
There are many devices on the market that fall under the moniker “wearable.” In order to better
understand the current market, PODS compiled a list of devices currently available to users.
Table 3. Market Devices
Device Name
Details
Price Point
Display
Weight
Fitbit Charge HR
Reflectance heart rate monitor
194.95
OLED
0.8 oz.
99.98
None
0.8 oz.
$17.78
LED
1.8 oz.
$19.99
OLED
0.32 oz.
$1,348.00
LED or
N/A
Monitors sleep and steps
Phone and web app
Worn on Wrist
Wi-Fi and Bluetooth sync
Jawbone UP 24
Tracks movement and sleep
Wifi and Bluetooth Sync
Worn on wrist
CMS 50-DL
Works for 40 continuous hours.
Pulse Oximeter
Transmittance oximeter.
Worn on finger
EMS500a
Worn on Finger
Transmittance oximeter
Adjustable audio alarm for blood
oxygen level
Nonin 3150
Bluetooth and USB sync
Finger sensor with wrist display
OLED
Transmittance oximeter
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Requirements
Wearable devices range in applications from medical to fitness. Consumers will expect similar features
and these needs to be balanced with the focus PODS has on pilots. The three requirement areas PODS
chose are functional, performance, and interface. Functional requirements list how the device should
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operate. Performance requirements list what should be quantifiably expected of the device. Interface
requirements list what the user should expect from interacting with the device.
Functional requirements
1. The band of the device should be comfortable to wear for 24 straight hours. This means it’s
sweat/water resistant, should be made of a skin friendly material, and be adjustable to fit most
wrists.
2. The LEDs and photodiodes should lay as flush to the skin as possible to minimize noise to the
photodiodes and prevent them from rubbing in an uncomfortable manner
3. The device should display accurate and timely data based on actual measurements.
Performance requirements
1. The battery life needs to be long enough so that the device lasts through a flight of 8 hours. If the
battery doesn’t last for that long, then it isn’t serving its purpose to protect a pilot during an entire
flight.
2. The hardware should be able to process at a rate of 30 Hz to display timely and accurate data
3. The display resolution should be high enough to distinguish the text at 4 feet. If a pilot were to
glance at the device at arm’s length, assuming good vision, he should be able to read it.
4. The accuracy of the data displayed should be within 2%. Because of the premise for building the
device being to prevent a condition which has a small tolerance for error, anything less than 2%
would put the pilot at risk.
Interface requirements
1. The interface should be intuitive to use so that the pilot doesn’t have to spend too much brain
power operating it. The goal of the device is to prevent crashes so if the interface warns the pilot
of low blood oxygen level but the pilot crashes because he’s messing with the interface, the
device is not accomplishing its goal.
2. Minimize clicks on a screen and from one screen to another. This is a follow up to the previous
point about intuitive interface. Each click represents time when the pilot should be focusing on
flying therefore minimizing clicks will allow a pilot to minimize the risk of crashing because of
distraction rather than low oxygen level.
3. Menus should use plain language and non-technical terms. Pilots are not engineers so the menus
and setting need to spell out what they do in plain language.
4. Buttons should be big enough to press with large fingers. A user will expect the buttons don’t
require a huge amount of precision and concentration to press.
5. Text should be as large as possible. PODS wants to minimize distractions and the larger the text,
the less time the pilot has to spend trying to read what the text says.
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PODS deliverables for the project are:
1. The Project Proposal and Feasibility Study
2. Final Report
3. Team website
4. Reflectance prototype
5.1 Design Schedule
The schedule below shows the breakdown schedule of the design work that the team did this past
semester.
Table 4. Fall Work Breakdown Schedule
Task Name
Duration
Start
Finish
Predecessors
Fall 2014
44 days
Wed 10/8/14
Mon 12/8/14
Oral Presentation
2 days
Fri 10/10/14
Mon 10/13/14
Project Brief for
6 days
Wed 10/8/14
Wed 10/15/14
Project website
7.5 days
Mon 10/13/14
Wed 10/22/14
Project poster
8 days
Wed 10/22/14
Fri 10/31/14
PPFS
44 days
Wed 10/8/14
Mon 12/8/14
Introduction
1 day
Wed 10/8/14
Wed 10/8/14
Background & Research
1 day
Thu 10/9/14
Thu 10/9/14
7
Scope
2 days
Fri 10/10/14
Mon 10/13/14
10
Design Criteria
3 days
Tue 10/14/14
Thu 10/16/14
13
Design Alternatives
2 days
Fri 10/17/14
Mon 10/20/14
18
Feasibility
1 day
Tue 10/21/14
Tue 10/21/14
21
Cost/budget
1 day
Wed 10/22/14
Wed 10/22/14
22
Schedule
1 day
Thu 10/23/14
Thu 10/23/14
23
Business plan
1 day
Fri 10/24/14
Fri 10/24/14
24
Conclusion/review
1 day
Mon 10/27/14
Mon 10/27/14
25
Appendix
1 day
Tue 10/28/14
Tue 10/28/14
26
Rough draft
24 days
Wed 10/8/14
Mon 11/10/14
Review/polish PPFS
5 days
Tue 11/11/14
Mon 11/17/14
Industrial consultant
28
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Table 5. Spring Work Breakdown Schedule
Task Name
Duration
Start
Finish
Mon 2/2/15
Wed 5/13/15
Mon 2/2/15
Mon 3/31/15
Reflectance Prototype
Tues 4/1/15
Tues 5/12/15
Building Prototype
Tues 4/1/15
Fri 4/10/15
Iterative Design
Mon 4/13/15
Tues 5/12/15
Mon 3/30/15
Tues 5/12/15
Tkinter GUI
Mon 3/30/15
Fri 4/17/15
Pygameui GUI
Mon 4/20/15
Tues 5/12/15
Mon 4/27/15
Fri 5/8/15
Spring 2015
Transmittance Prototype
42 days
GUI
Housing
5.2 System Architecture
In the following sections, the system architecture is broken down into individually described components.
Below is a Level 1 block diagram of the system hardware.
Figure 1. Level 1 Block Diagram
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5.2.1 Probe
The probe component seen above consists of two different wavelength light-sources and a light sensor.
The light sources will be the emitters of red and infrared light needed for pulse oximetry, the non-invasive
measurement of blood oxygen saturation. The light emitters will require a source of power and could be
controlled by the microprocessor used in the system in order to manage the amount of power expended.
The photo sensor in the probe will measure the light transmitted through or reflected off of the user’s
skin. The light seen by the sensor is used to calculate oximetry data. The sensor is connected to the
amplifier used in the system. On the mechanical side, the probe, in addition to housing the light-emitters
and the photo sensor, will be able to be comfortably worn by the user while maintaining the proper
contact required to measure oximetry data.
5.2.2 Amplifier and Filter
The signal from the probe’s photo sensor is amplified so that the appropriate signal processing can be
accomplished. The amplifier will be multi-staged, with a minimum of a voltage amplification stage and
an output stage. Additionally, the team designed a passive low pass filter which eliminated unwanted
noise and prevent signal aliasing. The interface between the amplifier and the probe consists of a ground
and signal wire. The amplifier and filter required a power source and provided the amplified signal to the
analog to digital converter.
5.2.3 Analog to Digital Converter
The analog to digital converter (ADC) creates a discrete-time digital signal for processing by performing
a differential conversion of the continuous amplified and filtered analog signal and the output voltage of
the reference digital to analog converter. The converter’s specifications - such as resolution, sampling
frequency, bandwidth, and accuracy - are appropriate for the range of signals produced by the amplified
and filtered photo sensor. Like the probe and amplifier, the ADC requires a power source and will
interface with the amplifier and filter system component through ground and signal wires.
5.2.4 Digital to Analog Converters
The digital to analog converter (DAC) converts a digital value specified by the microprocessor to an
analog voltage. The system contains two DACs: a reference DAC whose purpose is to keep the
differential voltage values being converted by the ADC within its voltage range by providing a reference
voltage and a brightness regulating DAC whose purpose is to adjust the brightness of the LEDs so that
they are at the ideal brightness level for pulse oximetry by regulating the voltage on the LEDs’ cathode.
The output voltage of both DACs is adjusted by the microprocessor via the control system software. Each
DAC requires a power source and interfaces with the LEDs and ADC through output voltage wires.
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5.2.5 Microprocessor
The system’s most vital component, the microprocessor, performs all the processing of the oximetry data
in order to produce values representing blood oxygen saturation and heart rate to be displayed on the
graphical user interface. Additionally, the microprocessor runs the algorithms designed to monitor the
user’s blood oxygen saturation and issue warnings when blood oxygen saturation level drops below the
specified threshold. The important aspects considered when selecting the microcontroller were: price,
power consumption, number and type of inputs and outputs (I/O), and application suitability. Other
factors which were considered because it adds desirability but not required are: built in analog to digital
converter, integrated antenna, Linux based operating system, and pre-programmed communication
protocols. The microprocessor interfaces with the ADC and DACs through an I2C bus connection.
5.2.6 Display Driver
The display driver takes the intended output from the microprocessor for the display and generates the
appropriate signals to create the intended graphics. At a high level, the display driver interfaces between
the display and the microprocessor. The display driver is built into the display used for this system.
5.2.7 Display
The display provides a visual for the data, graphics, and warnings as well as the other necessary
information to the user. The display’s size and resolution accurately display the information from the
microprocessor such as of heart rate and blood oxygen saturation. The display shows the warnings related
to blood oxygen levels in a readable fashion.
5.2.8 Speaker
The speaker provides auditory warnings to the pilot when triggered by the microprocessor. The speaker
must be loud enough to combat the noises found the cabin of a small aircraft and be clearly
distinguishable from other possible warnings from the airplane itself (i.e. stall warnings, autopilot
disengage, et al). The speaker interfaces with the microprocessor and is housed in either the display or
microprocessor module.
5.2.9 Software
A block diagram of the various software modules and their subsequent interfaces can be seen in the figure
below.
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Figure 2. Hardware/Software Interface Block Diagram
5.2.9.1
Data Acquisition
The data acquisition module performs the setup of the ADC and initiates conversions based on the
sampling frequency specified. Additionally, the data acquisition module stores the results of the
conversions into a data structure so that it may be processed by the signal processing and control system
modules. The primary is written effectively and requires very little processing resources. The data
acquisition software will interface with the ADC through an I2C bus library.
5.2.9.2
Signal Processing
The signal processing module’s purpose is to analyze the ADC data collected by the data acquisition
module and perform a range of operations such as filtering and signal characterization. Algorithms used
to filter and characterize the raw data must be of a low time complexity in order to ensure that real-time
data can be output to the user. The results of the filtering and characterization algorithms will be stored in
a data structure for the oximetry module to access. The signal processing module will interface with the
data acquisition module by reading the stored conversion data.
5.2.9.3
Control System
As its name suggests, the control system module’s function is to analyze the data gathered by the data
acquisition module in the closed loop system and provide adjusted feedback in the form of voltage values
sent to the reference and brightness regulating DACs. The control system module will use low time
complexity algorithms to calculate all necessary adjustments to the system. The interface between the
control system and data acquisition module will occur by reading the stored conversion data.
5.2.9.4
Oximetry
The oximetry module’s purpose is to take the processed data provided by the signal processing module
and perform heart rate and blood oxygen calculations. Additionally, the oximetry module is responsible
17
for determining if warnings must be issued to the user based on the blood oxygen levels calculated. The
heart rate, blood oxygen level, and warning flag are output to the graphical user interface by passing the
values to a set of member functions. The oximetry module will interface with the signal processing
module by reading the processed data.
5.2.9.5
Graphical User Interface
The graphical user interface (GUI) module’s purpose is to create a user interface for rendering on the
display. The GUI module will display the heart rate and blood oxygen data and will also generate visual
warnings when the user’s blood oxygen level is too low. As the name implies, the GUI module provides
the interface between the user and the product. The GUI module will interface with the oximetry module
by exposing a series of methods which update the generated user interface.
5.3 Design Norms
Trust
“Design should be trustworthy, dependable, reliable, and avoid conflicts of interest”
Due to safety being the primary goal of this project, the design norm of Trust is paramount. This project is
frivolous without a pilot putting their trust into using the device to correctly measure, monitor, and
communicate blood oxygen levels to prevent hypoxia. Furthermore, this trust encompasses all levels of
design, production, and application; with potential life and limb at risk, all aspects of the device must be
dependable, safe, and reliable in many circumstances and environments since a malfunction could result
in danger for the user. Finally, the reliability of the device is extremely important since the task of flying
an airplane is a demanding and often stressful process. Therefore, the pilot should not have to worry
whether the device is functioning properly and trust in it if it could fail at a crucial time. To ensure that
this device is trustworthy, the team will be using a three phase testing plan and posting the results of the
test on their website. In this way, each user can know how thorough PODS was in the construction of this
device.
Transparency
“Full disclosure both in the design process and to the public, regarding options, effects, defects, and
tradeoffs.”
Similar to the design norm of Trust, the norm of Transparency is crucial to this project. In order to
establish trust with the users, all relevant details of the project must be disclosed. If any defects are
discovered, these absolutely must be disclosed since a failure to do so could result in fatal crashes. Also,
all effects of the device on the user’s ability to operate an aircraft be must be disclosed immediately in
18
order to stay true to the project’s core goal of preventing crashes. Finally, transparency includes providing
the performance tests and corresponding results to identify the limitations and feasibility of application
for this device under different circumstances. Disclosing as much relevant information as possible
contributes the user’s sense of security thus building a relationship of trust which is why the testing
results will be posted publicly on the team’s website.
Integrity
“Design should have completeness, harmony of form and function, promote human values and
relationships, and be pleasing and intuitive to use”
The final design norm identified for this project is Integrity. This design norm offers the user closure and
value when using the device. Closure in the sense that it was created with them in mind to relieve the
mental burden of having to worry whether the device is functioning properly and value through keeping
them safe by using an intuitive and well thought-out interface. The design norm of Integrity heavily
affects the design of the user interface on the display system as the norm dictates that the interface must
be both pleasing to use and highly functional. The design norm of Integrity also complements the design
criteria of ergonomics and dictates that the ergonomics of the device should also be balanced with its
functionality. This is specifically seen in the display and warning system components of the device. The
requirement for those components is specifically taken from this design norm because it is the bridge
between the user and the device. This bridge takes what is going on behind the scenes and presents it in a
way which is pleasing and intuitive to use. With these considerations in mind, the device will be the very
example of integrity.
5.4 Design Components
5.4.1 Physical Device (Probe)
5.4.1.1
Design Criteria
The physical design of the pulse oximeter must be comfortable and easy to wear. If it is inconvenient to
put on or wear, users will not be as likely to buy or use it. The design focused on making the pulse
oximeter into a small band that is worn around the wrist. This will allow for users to have a full range of
motion in their hands and fingers, a large improvement over the current pulse oximeters on the market.
This new pulse oximeter will be comfortable for users to wear as they go about their daily activities.
19
5.4.1.2
Design Alternatives
5.4.1.2.1
Headset
The majority of pilots wear some form of headset to eliminate outside noise and communicate with the
tower and other passengers. Reflectance oximetry would lend itself to this design. It is also possible that
with some clever design work, transmittance oximetry could work by putting the sensor in the headset.
The argument for putting the sensor in the headset is that the headset already has a wired connection to
the plane, allowing the design to take advantage of that wire, minimizing the hindrance and danger to the
pilot. The current costs of headsets may prove to be the biggest detriment as researching and prototyping
would be difficult for this project and its budget.
5.4.1.2.2
Bracelet
A bracelet would take advantage of the reflectance oximetry and could be made large enough to have a
power supply to support wireless capability. It also would not limit the dexterity of a pilot's fingers. The
biggest challenge related to this design is that the bracelet needs to remain comfortable for the whole
flight all while it must maintain good contact with the skin for accurate oxygen readings.
5.4.1.2.3
Finger Attached
A sensor in a ring or clip on device for the finger is currently available on the open market. This allows
for easier research and prototyping, but may limit the wired/wireless options. The simplicity and small
design of the device lends to comfort and allowing good mobility for the pilot, but also presents heavy
constraints on the size of the device.
5.4.1.3
Design Decision
The table below shows the decision matrix for the different physical devices with a maximum possible
score of 5 for each category. The decision is based off cost to implement, mobility for the pilot, design
aspects and, size. From this decision matrix it was decided that a Bracelet design is the best option for this
project.
Table 6. Finger Device Decision Matrix
Headset
Bracelet
Finger Attached
Cost
1
3
2
Mobility
4
4
3
Design
3
3
1
Size
3
3
4
Total
11
13
10
20
5.4.1.4
Prototype Housing
With the decision being made to create a bracelet device, the team then needed to determine how to build
this housing. The alternatives for this decision are shown in the table below. From this design matrix it
was determined that the best solution is to 3D print the prototype housing out of a plastic material. This
gives the greatest flexibility and customization for the housing.
Table 7. Prototype Housing Decision Matrix
3D print
Purchase
Metal
Cost
3
3
4
Customization
5
1
3
Design
4
3
3
Size
5
2
3
Total
17
9
13
5.4.2 Oximetry
5.4.2.1
Design Criteria
The oximetry method for this project must be able to accurately measure blood oxygen levels while not
limiting the users’ range of motion. The two methods of oximetry that the group considered are
transmittance oximetry and reflectance oximetry. The oximetry method must be un-invasive and not
disrupt the user in any way.
5.4.2.2
5.4.2.2.1
Design Alternative
Transmittance Oximetry
Transmittance pulse oximeters measure blood oxygen saturation by producing two beams of light at
different wavelengths (red and infrared) via light-emitting diodes (LEDs) and by measuring the light
transmitted through the user’s fingertip via photodiodes1. Transmittance pulse oximeters make up the
vast majority of consumer pulse oximeters.
5.4.2.2.2
Reflectance Oximetry
Reflectance pulse oximeters also produces two beams of light but instead of measuring the light
transmitted through the user’s skin, it measures the light reflected by the user’s skin. From a
design perspective, the primary difference between the two is that a reflectance pulse oximeter
does not require a thin section of the user’s body in order to obtain measurements. A recent study
21
on the differences of transmittance and reflectance pulse oximetry published in the Anesthesia &
Analgesia Journal showed that both methods were equivalent in accuracy and performance1.
5.4.2.3
Design Decision
The table below shows the decision matrix for oximetry. The two alternatives were judged based on four
characteristics. From this design matrix, it was determined that reflectance oximetry would be the best fit
for this project.
Table 8. Oximetry Decision Matrix
Transmittance
Reflectance
Implementation
4
3
Wear-ability
2
5
Design
3
5
Signal Fidelity
4
3
Total
12
16
5.4.3 Light Source and Sensor Network
5.4.3.1
Design Criteria
The light source must operate at different wave lengths suitable for reflectance pulse oximetry.
Additionally, the sensors must be able to collect the light reflected from the user’s skin. The light source
needed to operate in the red and near-infrared spectrum and the sensor should have a large area for
increased detection. The wavelength of light isn’t as important for heart rate as it is for blood oxygen
level2 which is why the team decided on 660 nanometers and 940 nanometers.
5.4.3.2
Design Alternatives
PODs was constrained to use photodiodes and light emitting diodes (LEDs). This is because the
alternatives to these were not small enough, took too much power, or did not have the correct properties.
PODS looked into phototransistors and laser diodes however they weren’t readily available as matching
pairs.
1
2
(Wax 2009)
(Pujary n.d.)
22
5.4.3.3
Design Decision
PODS chose LEDs that operated at 660 and 940 nanometers. This component had a common anode and
matching photodiodes. This means that the spectral response of the photodiodes was created for the
LEDs. PODs also chose these components because they were generously provided as samples by OSI
Optoelectronics.
5.4.4
Display System
5.4.4.1
Design Criteria
The display must be able to warn the user when they are starting to suffer from symptoms of hypoxia. If
the user becomes confused, this system must display the data in an easy to understand way so its
interpretation is comprehensible. The display must be designed to be small for easy mounting in the
cockpit. The display must withstand turbulence and flight-like conditions. The warning system must be
based on the level of oxygen in the blood. The data received from the sensors is interpreted by the
warning system and displayed. This system will give status messages to the pilot. The warning system
will issue warnings before the pilot reaches a critical state.
5.4.4.2
5.4.4.2.1
Design Alternatives
Touch Screen
A touch screen display would both provide the user with the ability to interact with the program through a
graphic user interface.
5.4.4.2.2
Smartphone App
The app would take the place of the display and would subsequently lower the cost of development and
the cost of the finished product. Having the display system on the user’s smartphone would also remove
the need for an external display and lower the overall cost of the product.
5.4.4.3
Design Decision
The team decided to design an external touch screen display. The main reason for this was the fact that it
was easier to implement into the project while still providing all the capabilities desired. Additionally,
designing a smartphone app on top of a touch screen display did not improve the device’s capabilities by
enough to justify spending the time developing the app. A decision matrix between the touch screen and
smartphone app can be seen in the table below.
23
Table 9. Display Decision Matrix
Touch Screen
Smartphone
Implementation
4
2
Design
3
3
Ease of use
3
3
Total
10
8
5.4.5 Hardware/Display System Interface
5.4.5.1
Design Criteria
The display system and external hardware (i.e. ADC, DAC, sensor circuit, LED circuit) must be able to
interface with each other at data rates fast enough that the system’s performance is not bottlenecked. This
interface will determine if the final design will consist of the two components, the external hardware and
the display system, or if it will be one integrated device.
5.4.5.2
5.4.5.2.1
Design Alternatives
Wired
One option for connecting the oximeter sensors and circuitry with the microprocessor and display system
is by using a hardwired connection. The benefits of using a hardwired system include: low-cost, no speed
restriction, no additional power consumption. Drawbacks of using a wired connection include: vulnerable
to fraying and degradation, potentially could snag on the many controls in a cockpit, could inhibit pilot’s
range of motion, and physically limits the placement of the display system.
5.4.5.2.2
Wireless
Alternatively to a wired connection, a wireless system could be used in order to connect the oximeter
sensors, circuits, and microprocessor to the display system. Within wireless systems, there are a number
of technologies which must be considered individually, however, there are some benefits that they all
share. A few such benefits include: no limits on the pilot’s range of motion, eliminating the possible
snagging and general physical limitations of wires, overall flexibility. Conversely, a few drawbacks
include: additional power consumption, additional cost, additional complexity and circuit board space. A
table summarizing the details of each of the three wireless technologies described in the proceeding
sections can be seen below.
24
Table 10. Bluetooth/WiFi/ZigBee Comparison Summary
Bluetooth
WiFi (IEE 802.11n)
ZigBee
Operating Frequency (GHz)
2.4
2.4 and 5
2.4
Range (m)
10
1-100
1-100
System Resources (kB)
250
1,000
4-32
Data Rate (Mb/s)
5.76
600
2
Power Consumption
Medium
High
Very Low
5.4.5.2.2.1 Bluetooth
Bluetooth is a type of wireless technology which utilizes radio frequencies over a spectrum 2.4 to 2.485
GHz in order to achieve wireless communication3. Bluetooth also uses a technology called adaptive
frequency hopping in order to minimize interference with other radio waves present across its frequency
spectrum. The maximum range of a Bluetooth device is roughly 10 meters3. When compared to ZigBee
and WiFi, Bluetooth achieves moderate battery consumption4. Finally, Bluetooth uses about 250 kB of
system resources and has a maximum data rate of 5.76 Mb/s.
5.4.5.2.2.2 WiFi (IEE 802.11)
WiFi, also known by the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11 (in the
context of this report, 802.11n will be used), is a wireless technology which operates in the 2.4 and 5 GHz
bands5. WiFi, whose primary goal is high data rates, has a maximum data of 600 Mb/s and uses over 1
MB of system resources. WiFi also has a range anywhere from 1 to 100 meters. Although WiFi has very
high speeds, when compared to ZigBee and Bluetooth, it has very high power consumption4.
5.4.5.2.2.3 ZigBee
ZigBee, the final type of wireless technology considered for the proposed design, operates in the 2.4 GHz
frequency band. ZigBee uses between 4 kB to 32 kB of system resources and achieves data rates up to 2
Mb/s4 over a range of 1 to 100 meters. ZigBee, whose primary design features are low-cost and lowpower, has very low power consumption when compared to WiFi and Bluetooth. Another unique feature
of ZigBee, in addition to very low power consumption, is ZigBee’s ability to support extremely large
mesh networks (over 64 devices)4.
3
(A Look at the Basics of Bluetooth Technology n.d.)
(ZigBee Technology n.d.)
5
(IEEE 802.11 Standards Tutorial n.d.)
4
25
5.4.5.2.3
Integrated
A final option for the device would be to design and build all of the hardware including the
microprocessor, display, and battery so that the combined size of all the components is small enough to be
worn comfortably around the wrist. The benefit of going with an integrated design is that it offers a
superior amount of comfort compared to the wired connection and also eliminates the complexity of
having two separate physical devices—a wrist-worn device containing the sensors and a separate
display—by incorporating the hardware and display in one package. The drawbacks of going with an
integrated system are that it would heavily constrain the physical size of the microprocessor and display
and would also be exceedingly difficult, if not impossible, to build as a prototype.
5.4.5.3
Design Decision
When choosing the interface between the external hardware and the display system, the team considered
four criteria: ease of integration, consumer appeal, cost, and power consumption.
Table 11. Hardware/Display System Interface Decision Matrix
Integrated
Wired
Wireless
Ease of integration
5
5
2
Consumer appeal
5
1
3
Cost
2
5
3
Power Consumption
4
5
4
Total
16
16
12
5.4.6 Microprocessor
5.4.6.1
Design Criteria
The team identified five key criteria which the microprocessor must meet: cost, processing power,
hardware flexibility, software flexibility, and size. Cost was considered to minimize the cost of the final
design. Processing power (clock speed, RAM, graphics processors, etc.) was considered because the
microcontroller must run various algorithms for oximetry computation, LED voltage control, and
monitoring in addition to providing a graphical user interface. Hardware flexibility was considered
because, the microprocessor will need to interface with devices like the analog to digital converter
through different protocols and be able to utilize Bluetooth, WiFi, or ZigBee. Software flexibility was
considered because the software for oximetry measurement and monitoring, graphical interface, and
interfacing with hardware require various high-level languages and libraries. Finally, size was considered
to align with the design criteria of ergonomics.
26
5.4.6.2
5.4.6.2.1
Design Alternatives
Raspberry Pi B+
The Raspberry Pi B+ is a single board computer with much of the same functionality as a full sized
computer. This single board computer supports Linux operating systems.
5.4.6.2.2
Arduino Yun
The Arduino Yun is a single board computer similar to the Raspberry Pi. It is based on the ATmega32u4
and the Atheros AR9331. This single board computer supports Linux operating systems.
5.4.6.2.3
Jennic JN5148
The Jennic JN5148 is a high performance single chip. The benefits of this board is its very low power
consumption while maintaining high performance.
5.4.6.3
Design Decision
In order to choose which processor to use, the team placed the considerations outlined earlier into a
decision matrix with equal weighing and maximum possible scores of five which can be seen in table
below.
Table 12. Microprocessor Decision Matrix
Raspberry Pi B+
Arduino Yun
Jennic JN5148
Cost
3
1
5
Computing Power
5
4
1
Software Flexibility
5
3
1
Hardware Features
5
5
2
Size
2
3
5
Total
20
16
14
As seen in the table, the Raspberry Pi B+ was determined to be the best microprocessor package for the
project. One key feature of the Raspberry Pi which distinguished itself from the other considerations was
an onboard graphics processor as this will enable the final design to be able to provide a low latency
graphical display of oximetry readings as well as real time graphs of things like heart rate. Another key
feature of the Raspberry Pi was its status as a single board computer and its subsequent ability to compile
and run high level languages like Python, C/C++, and Java as this will allow the software to be developed
in almost any language desired.
27
5.4.7 Filtering
5.4.7.1
Design Criteria
The filters in the design must filter out primary sources of noise in the signal. Circuitry connected to VDD
should have low pass filters in order to eliminate any noise from the power source. At a bare minimum, a
filter must be designed to eliminate any aliasing that would occur due to sampling frequencies higher than
the system’s Nyquist sampling rate.
5.4.7.2
5.4.7.2.1
Design Alternatives
Hardware Filter
Passive filtering could be performed using passive components such as resistors, capacitors, and
inductors. Additionally, the filtering could be done with an active filter comprised of resistors, capacitors,
inductors, and amplifiers. The benefit of hardware filtering is that it is the only way to filter noise from
the power supply and provide antialiasing. A few of disadvantages of hardware filtering include: low
flexibility, occupies circuit/physical space, low latency, and requires power if active.
5.4.7.2.2
Digital Filter
Filtering of the sampled sensor signal could be achieved through digital filtering using various filtering
software algorithms. The primary benefits of using a digital filter are high flexibility and practicality. The
primary drawback of using a digital filter is high latency depending on the filter complexity.
5.4.7.3
Design Decision
Due to the fact that digital filtering could not provide antialiasing and decoupling, the team was
constrained to using hardware filters for these purposes. The filter used to clean up the data gathered by
the sensors, however, was not constrained and thus the team created a decision matrix with the criteria of
flexibility, practicality, latency, and physical size. Each category was weighted equally and can be seen in
the table below.
Table 13. Filter Decision Matrix
Hardware Filter
Digital Filter
Flexibility
1
5
Practicality
2
5
Latency
5
2
Physical Size
1
5
Total
9
17
28
Based off of the decision matrix, the team chose to use a digital filter via software for filtering the
sampled signal. The digital filter proved itself to be the best decision due to its high flexibility and ability
to perform high order filtering which would normal be highly unpractical if built in hardware.
Specifically, the team chose to use a 7th order Chebyshev low pass filter with a cut-off frequency of 4Hz
based off of research and testing.
5.4.8 Analog Signal Conversion
5.4.8.1
Design Criteria
The analog signal coming from the sensor must be converted into digital data so that the microprocessor
can then process and analyze the signal. The component which performs the conversion must ensure that
no information about the original analog signal is lost when the conversion is performed.
5.4.8.2
Design Alternatives
The only component which performs an analog to digital signal conversion is an ADC which the team
was subsequently constrained to use.
5.4.8.3
Design Decision
When first choosing which ADC to use, the team considered the 16-bit, 500 samples/second Maxim
MAX1416, the 10-bit, 200k samples/second Microchip Technology MCP3008 and the 12-bit 100k
samples/second Microchip Technology MCP3202. One thing to note about the possible choices
identified is that only dual in-line package (DIP) chips were considered as they offer the most flexibility
for prototyping on breadboards. The four features considered when evaluating which analog to digital
converter to use included: sampling frequency, resolution, number of channels, power consumption, and
additional features. These features were then scored out of five and placed in a decision matrix seen in
the table below.
Table 14. Analog to Digital Converter Decision Matrix
MAX1416
MCP3008
MCP3202
Sampling Frequency
1
5
4
Resolution
5
2
3
Number of Channels
3
5
3
Additional Features
5
0
0
Power Consumption
5
2
2
Total
18
14
12
29
The result of the decision matrix is that the Maxim 1416 ADC is the best choice for the project. A few of
the important categories which it proved to be the best option was in resolution, power consumption, and
additional features. Although 16-bits may be a higher resolution than is needed for the final design, the
team determined that for the prototype, it was best to go with a high resolution as it provided the most
room for data analysis. The MAX1416 proved to be the best choice for power consumption as, according
to its datasheet which can be seen in the appendix, its max power consumption is 1mW whereas the two
Microchip Technology ADCs have a max power consumption of 3mW. Finally, the MAX1416’s
additional features of a programmable gain amplifier (PGA) and digital filtering was key in distinguishing
itself from the other ADCs as these two features eliminate the need for an additional preamplifier and
filter network between the probe and the ADC.
After purchasing and wiring up the MAX1416 ADC, however, the team was not able to get any data from
the ADC. The team spent numerous hours debugging the ADC with no success and ultimately decided to
choose a different ADC. For the decision of which ADC to use, the team used the same criteria as in the
Product Proposal and Feasibility Study (PPFS) and added the Texas Instruments 12-bit ADS1015 to the
list of possible ADCs. The decision matrix can be seen in the table below.
Table 15. Analog to Digital Converter Decision Matrix
ADS1015
MCP3008
MCP3202
Sampling Frequency
3
5
4
Resolution
3
2
3
Number of Channels
5
5
3
Additional Features
3
0
0
Power Consumption
5
2
2
Total
19
14
12
Just as with the Maxim 1416, the Texas Instruments ADS1015 proved to be the best choice over the other
options due to its resolution, low power consumption, and built in PGA. It is also worth noting that the
ADS1015 was significantly smaller than the other options due to being a QFN (quad flat no-leads)
package as opposed to DIP, but was still able to be used for prototyping on breadboards as the ADC could
be purchased on a breakout board.
30
5.4.9 Digital Signal Conversion
5.4.9.1
Design Criteria
The digital signals calculated and controlled by the software for reference and LED voltage must be
converted from digital data to analog voltages so that they may be applied to the differential input of the
ADC and the LED circuit respectively.
5.4.9.2
Design Alternatives
Just like the ADC, the only component which performs a digital to analog signal conversion is a DAC
which the team was subsequently constrained to use.
5.4.9.3
Design Decision
When choosing which DAC to use, the team identified four key features desired from a DAC: resolution,
accuracy, physical size, and power consumption. Resolution was chosen as one of the key features as the
DAC must be able to be set to a high range of different voltages for the reference point in the differential
conversion performed by the ADC. Accuracy was chosen as a key feature as inaccuracies in the DAC’s
output voltage would directly affect the reconstruction of the DC component of the sensor circuit’s signal.
Lastly, physical size and power consumption were chosen as the final key features as low power
consumption and a small package size would improve the feasibility of building an integrated device.
The team considered two DACs for use in the design: the 12-bit Microchip MCP4725 and the 10-bit
Analog Devices AD5611. These two DACs and the key features identified were placed in a decision
matrix with max scores of five for each category seen in the table below.
Table 16. Digital to Analog Converter Decision Matrix
AD5611
MCP4725
Resolution
3
5
Accuracy
2
5
Power Consumption
5
3
Physical Size
5
4
Total
15
17
Based off of this decision matrix, the Microchip MCP4725 was chosen to be used for the design.
Although the Analog Devices AD5611was comparable in most categories, the MXP4725 ultimately
proved to be the superior choice due to having a higher resolution by 2 bits and a ±2 LSB INL as opposed
to the AD5611’s ±4 LSB INL (least significant bit integral non-linearity).
31
5.4.10 Graphic User Interface (GUI)
5.4.10.1 Design Criteria
The GUI for this system must focus on simplicity in both design and function. It must be easy to navigate
and understand. It must be easy for the user to pick up and quickly understand the function of the GUI
and be able to use it effectively. It must work on the touch screen display. It should be able to work on a
raspberry pi and be easily adaptable to other operating systems.
5.4.10.2 Design Alternatives
5.4.10.2.1 Tkinter
Tkinter is the most popular GUI development program used for python. It is a preinstalled package with
python and is easy to develop with. Additionally, the documentation on how to develop a Tkinter GUI is
extensive and readily accessible.
5.4.10.2.2 Pygameui
Pygameui is a GUI development library that is based on Python’s Pygame library. This program is rough
in its development but provides the user with similar features to a Tkinter GUI. Pygamui GUIs can be run
on a Raspberry Pi straight from the terminal eliminating the need to be run with operating system’s
graphical user interface. Pygameui also has visually appealing graphics.
5.4.10.3 Design Decision
In order to choose which GUI library to use, the team created a decision matrix with the criteria of
documentation, ease of development, graphics, and processing consumption. This matrix can be seen in
the table below.
Table 17. GUI Decision Matrix
Tkinter
Pygameui
Documentation
4
2
Ease of development
5
3
Graphics
1
5
Processing consumption
3
5
Total
13
15
Based on the results of the decision matrix, the team chose to use Pygameui for developing the GUI. This
choice was mostly due to the superior graphics quality of Pygameui compared to Tkinter. Although
32
Tkinter offered superior ease of development, the team determined that the visual appeal of the Pygameui
outweighed this drawback.
5.5 Integration, Test, and Debug
The team’s approach for integration, test, and debug was to create a sort of checklist which briefly
outlines the goal of the test being performed, the equipment used (if any), the experimental setup, and its
results. This list can be seen in the table below.
Table 18. Integration, Test, and Debug List
Objective
Equipment Used
Setup
Result
N/A
A jumper wire was placed
across the SPI pins on the
Raspberry Pi in order to send
the data over a closed loop
All the data sent was
received and read
successfully
Digital
Multimeter
(DMM), Power
Supply,
Oscilloscope
ADC was connected to the
Raspberry Pi via SPI. A
known voltage was applied to
the input pins of the ADC. The
oscilloscope was used to probe
the SPI pins for debug.
The ADC neither
performs conversions
nor sends any data
over SPI in response
to commands sent
Perform analog to digital
conversions with
ADS1015 ADC and read
them with the Raspberry Pi
DMM, Power
Supply
ADC was connected to the
Raspberry Pi via I2C. A
known voltage was applied to
the input pins of the ADC.
Test photodiode/sensor
circuit is wired correctly
and performing properly
Power Supply,
Oscilloscope
Oscilloscope probe was placed
on the load resistor to measure
the output of the sensor circuit.
Power Supply,
Oscilloscope
Oscilloscope probe was placed
on the load resistor to compare
the voltage measured by the
ADC with the actual voltage
on the input pin
Voltages from ADC
match voltages
measured by
oscilloscope
DMM
Output pin of DAC was
measured by DMM
Voltages values sent
to DAC by the
Raspberry Pi match
voltages measured
Send and receive data on
the Raspberry Pi via SPI
Perform analog to digital
conversions with
MAX1416 ADC and read
them with the Raspberry Pi
Test integration of sensor
circuit and ADC
Verify the firmware
developed for the DACs
and the DACs themselves
are functional
Data received by the
Raspberry Pi
corresponds to
voltage applied to
ADC’s input
Covering up/shining
light on photodiode
results in changes in
the voltage across the
load resistor
33
Test brightness regulated
LED circuit design
DMM
Test differential
measurement with DAC
and input voltage
DMM, Power
Supply
Test reference voltage
adjustment software
DMM, Power
Supply
Test transmittance
oximetry
hardware/software
prototype
Verify transferring
prototype hardware from
breadboard to perfboard
was successful
Test the fabricated
photodiode array
Test different
measurement spots for
reflectance oximeter
prototype
Commercial
Transmittance
Oximeter
DMM,
Commercial
Transmittance
Oximeter
DMM
Commercial
Transmittance
Oximeter
DMM was placed in series
with the LED to measure the
current flowing through the
LED
DMM was used to measure the
DAC’s output voltage, Power
supply was used to apply
different voltage values to the
input of the ADC
DMM was used to measure the
DAC’s output voltage, Power
supply was used to apply
different voltage values to the
input of the ADC
Transmittance oximeter
prototype was worn on one
finger while the commercial
oximeter was worn on another
Prior to testing, DMM was
used to probe the
perfboard/solders thoroughly.
Transmittance oximeter
prototype was worn on one
finger while the commercial
oximeter was worn on another
Prior to testing, DMM was
used to probe the circuit.
Photodiode array was
connected to sensor
circuitry/ADC for
measurements.
The reflectance prototype was
placed at different
measurement locations across
the body and compared to the
commercial oximeter
Brightness of LED
changes based on the
voltage supplied by
the DAC, current
does not exceed
maximum drive
current of LED
Differential readings
match the differential
voltage applied
DAC voltage changes
based on the input
voltage
Heart rates between
the two are nearly
identical, but SpO2
values are not
compared due to lack
of time to calibrate
Heart rates match,
data from PCB
hardware matches
breadboard data
Photodiode array
responded
appropriately to
different light levels
Signal recorded by
the reflectance
prototype is very
sensitive to motion
artifacts/particular
placement on body,
accurate heart rate
measurements only
34
occur on bottom of
wrist and forehead
Verify successful
integration of GUI and
software
Test accuracy of
reflectance prototype
SpO2 measurements
N/A
Commercial
Transmittance
Oximeter
The reflectance prototype was
used to take measurements,
prints to terminal containing
measurements were compared
to output on GUI
The values printed to
the terminal matched
the values being
displayed on the GUI
The reflectance prototype was
placed on the forehead while
the commercial oximeter was
worn on the finger to compare
results
Best R2 value
obtained correlating
the SpO2 from the
prototype and
commercial oximeter
was ~0.2, current
prototype is
inaccurate
6 Operations
6.1
Legal form of Ownership
This company will plan to be a limited liability company (LLC). The one main advantage to this form is
the protection from personal liability for business decisions and actions. If the company incurs any debt
along the way, the company’s members are safe in terms of their personal assets. This doesn’t mean that
the members are shielded from other acts of injustice in the workplace. The two other positives of an LLC
is the sharing of profits as the members see fit as well as much less record-keeping compared to other
forms of organization.
6.2
Company structure
35
Figure 3. Company Structure
6.3 Decision making authority
Each officer will have authority over each of their assigned teams in their department. All final
department decisions will be made by the chief officers. The final decisions of the company will
ultimately rest in the hands of the President, having the final decision making authority.
6.4 Significant compensation and benefits packages
As the PODS company is on the smaller side, the amount of compensation and benefits will be smaller
compared to the larger corporations. A 401K plan will be given to each employee, as well as some
employee stock ownership plans. Employees will also benefit from a total of two weeks paid vacation and
a few allotted sick days.
7 Industry Profile and Overview
7.1 Industry background and overview
The first device to measure blood oxygen saturation was developed by Karl Matthes in 1935. This device
is was much more crude and invasive than the simple finger devices on the market today. With a focus on
ergonomics and comfort, the pulse oximeters currently are easy to use and very accurate. The PODS
Company will focus on smaller design and better ergonomics while keeping the accuracy as important as
before. A more intuitive display system is also a major focus.
7.2 Major Customer Groups
7.2.1 Aviation
The initial purpose of PODS was to sell the design or products to airlines that were in need of a better
oximeter display system. The simplicity and ease of using the product would make the older pulse
oximeters obsolete. The design is geared more towards, but not limited to, the private pilots sector of
aviation.
7.2.2 Military
Similar to the private pilots, the air force may be able to use the product in the same manner. There would
need to be some high end adjustments as well as higher quality control for these applications, but they are
a possible consumer of the product.
36
7.2.3 Medical
The design of the PODS pulse oximeter could prove to be more beneficial to the everyday hospital
patient. The smaller device would cause less discomfort than the bulky finger ones used today, as well as
giving more important information to the nurses and doctors. Once again, the need for a high-end product
would put some pressure on the quality control of the devices sold to the medical field.
7.2.4 Emergency Response Units
The smaller design as well as the wireless display will prove to be much simpler for medical teams in
ambulances to use. Quicker and easier is the whole goal of these units, so the PODS product will be a
clear advantage.
8 Business Plan
8.1 SWOT Analysis
8.1.1 Strengths
A strength of the company is the uniqueness of the product. There are no pulse oximeters which are only
worn on the wrist so an opportunity exists to meet that need. Another strength of this company is the
ability to expand the into more than just the target market. The project was designed for the use by a
subsection of pilots but could move into other areas like medical devices.
8.1.2 Weaknesses
One of the weaknesses of this product is that people may not see the need for it. To combat this, a large
amount of resources will go into developing a marketing plan and advertising campaign explaining the
value in measuring blood oxygen saturation and added level of safety wearing it brings. Another
weakness is that it is a start-up company. PODS cannot take advantage of things larger companies have
access to like economies of scale, readily available capital, brand recognition, assets or investment.
8.1.3 Opportunities
There is a large opportunity for this company to grow quickly due to the uniqueness of this product. As of
yet, there is no product out on the market that meets pilots needs in the same way that this does. If this
product demonstrates reliability and improves pilot safety then there will be more opportunities to meet
customers’ needs.
8.1.4 Threats
A large threat is another company getting to market sooner with a similar product. To address this, the
product must get to market as quickly as possible in order to gain the largest chunk of the market. There is
37
also a risk of larger companies coming into the market with similar products but undercutting PODS’
established price point.
8.2 Marketing Strategy
8.2.1 Demographics
The demographic currently being researched is private pilots who fly non-pressurized airplanes. Another
demographic that the team is targeting are charter aviation companies that charter non-pressurized
aircraft. Pilots flying pressurized airplanes are not at high risk to hypoxia but hope to market to them on
the basis of pressurization failures and that it will generally improve their safety.
8.2.2 Customers' motivation to buy
Customer motivation to buy this product stems from it being comfortable to wear and improving a pilot’s
safety. These features along with an easy to read display will help a wrist worn pulse oximeter stand out
from others.
8.2.3 Market size and trends
The market for pilots is not incredibly large. It is estimated that there are 617,128 certified pilots in the
United States6. “...the market for pulse oximeters in the U.S., Asia Pacific and Europe is expected to grow
to over $1.3 billion by 2020. This market includes a range of monitors and sensors including bedside,
handheld and fingertip monitors; disposable and reusable sensors. Market growth can be attributed to cost
savings of reprocessed disposable sensors and the lower price point of consumer pulse oximeters that are
selling well through retail.”7
8.2.4 Advertising and promotion
8.2.4.1
Message
In order to best market this pulse oximeter system, the focus will be on two main factors: the safety that
comes from wearing the oximeter and the practicality of the design. The emphasis will be on the fact that
wearing a pulse oximeter for the duration of the flight increases pilot safety by reducing their risk to
hypoxia. A secondary emphasis will be placed on how easy the system is to use. The final emphasis will
be on how the pilot will barely notice wearing the device while flying.
6
(Pilot certification in the United States 2014)
(Pulse Oximeter Market Expected to Grow to over $1.3 Billion by 2020 in the U.S., Asia Pacific, and Europe
Combined 2014)
7
38
8.2.4.2
Media
The target market for this project is a very specific group of people and thus the team plans to market to
them mainly through the use of magazine and internet ads. The team will focus efforts on AOPA Pilot
Magazine, Flying Magazine, and Plane & Pilot Magazine. As for internet ads, using websites like Google,
Amazon and many aviation retailors should yield the best results.
8.2.4.2.1
Desired imagine in market
This product needs to be affordable to compete with low cost of a finger worn oximeter. With that said,
the number one concern is to make sure that the pulse oximeter is constructed with high quality parts. The
PODS brand should be something that can be trusted in the private aviation industry. It is also understood
that aviation in general is a very expensive hobby so pilots might be more willing to spend more money
on a device that will offer them an added level of safety.
8.2.4.2.2
Comparison against competitors’ prices
Most blood oxygen monitoring systems that include an external display are in the range of $1,000 to
$3,000. Most of these machines have more capabilities beyond blood oxygen monitoring. With the price
point of $500, the team’s product will be much cheaper than similar medical systems.
8.2.4.2.3
Discount Policy
The team will offer a discount policy for any company that buys ten or more devices. The team will
reduce the price by a set amount in hopes off incentivizing larger piloting companies to buy the team’s
product. As competitors enter the market, the team may have to decrease the product’s price in order to
stay competitive. The team is confident that despite these circumstances, a profit can still be made.
8.2.4.2.4
Gross Profit Margin
With the price point set at $500, the team anticipates a gross profit margin of 11%, 19% and, 23% for the
first three years of the business.
8.2.4.3
Distribution Strategy
PODS will mainly sell its product through online distributors. The team will employ at least one sales
person in the next few years whose job it will be to sell packages of the products to larger firms. The
warehouse will be located in the Midwest with easy access to most areas of the United States.
8.3 Competitive Analysis
8.3.1 Existing Competitors
There are two main competitors in this market. The first is Covidien and the second is Masimo. Both of
these companies produce various pulse oximeter devices that are used in health care settings.
39
8.3.1.1
Covidien
Recently acquired by Medtronic, they are a global healthcare products company and manufacturer.
Covidien was identified by iData Research as battling for the top spot in the global market for pulse
oximeters. Their focus is primarily on oximeters for medical uses such as homecare.
8.3.1.2
Masimo
Masimo is a manufacturer of patient monitoring products and is primarily known for their pulse
oximeters. In 2012, they were the number 1 seller of oximeters to hospitals and was identified as battling
for the top spot in the global market for pulse oximeters. While their primary focus is on oximeters for
hospitals, they recently released an oximeter that plugs into smart phones, targeting the aviation and sport
users.
8.3.2 Potential Competitors

Concord Health Supply

SantamedicalTM

Nonin Medical
8.3.2.1
Impact on the Business
Many of these companies have products similar to ours that are used as pulse oximeters for sports and
personal use. These companies have more experience marketing to pilots and also have brand names that
are known and respected in the industry. They each hold a large part of the market and would be hard to
compete with if they came out with a product similar to what PODS has come up with.
8.4 Cost Estimate
8.4.1 Development Costs
Development costs for the project are shown in the table below. These costs are based on the assumption
that engineering jobs cost the company $80 per hour. These costs do not include salaries of employees or
other cost other than costs that are specific to the development of the product.
40
Table 19. Development Cost
Hours
Total
Cost ($)
Specification
120
9600
Planning
1000
80000
Testing
1000
80000
Electrical Design
200
16000
Electrical Design Software
1500
120000
Marketing
100
8000
Industrial Design
500
40000
Hardware
2000
Prototypes
Total
4420
365600
8.4.2 Fixed Costs
Fixed costs for the first year of operation are shown in the table below. The costs are estimates based on
research done by PODS. The research was based off of cost that other small business experience.
41
Table 20. Fixed Cost
Fixed Costs ($)
Utilities (500 per month)
6000
Salaries
240000
Advertising
10000
Insurance ($30 per month)
360
Manufacturing
35100
Management
Employee Benefits
124650
Development
10000
Total
426110
8.4.3 Variable Costs
Variable costs for the first year of the business are shown in the table below. These costs are based off
producing 4000 units in the first year.
Table 21. Variable Cost
Variable Cost ($)
Direct Material
500000
Direct Labor
200000
Variable Manufacturing
100000
Employees
140400
Sales Commission
360,000
Shipping
20000
Total
1320400
8.5 Feasibility
From the calculation of the different costs associated with the project it was found that the design is
feasible. From the costs that have been estimated in the previous sections, the team believes that PODS
can be a profitable company. Over time the team will reduce the cost of the product after the initial startup
loan is paid back. A Pro-Forma Income Statement and Cash Flow Statement were used to analyze the
42
financial feasibility of PODS LLC. They are descried in the following sections of the report with the
tables provided in the appendix.
8.5.1 Income Statement
At a price point of $500 per unit the company has a net income after tax of $289,530 in the first year. In
the second and third year the company has net income after tax of $611,793 and $862,018 respectively.
8.5.2 Balance Sheet
A balance sheet is not included due to the fact that all inventory is used each year and all good produced
are sold. The assets of the company can be reduced to available cash. The company debt is simply the
bank debt at 10% interest rate while the equity is the original $50,000 invested in the company by the
owners.
8.5.3 Cash Flow Statement
From the cash flow statement PODS has decided to only reinvest what is needed for working capital and
to use the remaining profits to pay off company debt. This will help the company to reach its goal of
paying off its bank debt in six years.
8.5.4 Break-even Analysis
At the ideal price point for the product, 3,265 units need to be sold in the first year to break even. This
equates to 1,632,104 dollars of sales. After the first year, the number of units that need to be sold to break
even decreases due to the high startup design cost of the company. The break even sales volumes for year
two and three are $1,168,284 and $1,070,851, respectively.
8.5.5 Ratio Analysis
The ratio analysis is detailed in the appendix section of this report. From this it can be seen that the profit
margin for the first three years of the company’s life are 11%, 19% and, 23% respectively. This shows
that the team will be able to pay off bank debt and cover expensive that the company may encounter.
9 Prototypes
9.1 Transmittance Oximetry Prototype
This was the first prototype that the team developed for this project. The main purpose behind this
prototype was proof of concept. The team designed a system that could reliably measure heart rate and
blood oxygen levels. The team used this as confirmation that the design will work and used this to take
the next step towards designing a reflectance oximetry prototype. A picture of this prototype can be seen
in the figure below.
43
Figure 4. Transmittance Prototype
9.2 Reflectance Oximetry Prototype
This prototype was built to demonstrate the feasibility of the design solution. It was built by creating a
photodiode array with the LEDs in the middle that was then soldered to the other hardware. This
combined piece of hardware was then placed in a 3D printed housing which could be worn about the
wrist. This prototype was used for all of the hardware and software test to help finalize the design. This
prototype was built using iterative development were the team would do a test, find a problem, and then
try to solve this problem. This process was repeated numerous times in order to finalize the systems
software. Given more time, the team would like to do more work on this prototype and possibly build
another reflectance oximeter prototype applying the things learned in this design. A picture of this
prototype can be seen in the figure below.
44
Figure 5. Reflectance Oximeter Prototype
10 Deliverables
The purpose of this project was to design and build a prototype of a reflection oximeter system. From the
deliverables in this report future work will be able to be completed to produce a market ready device. The
deliverables for this report are listed below.
10.1 Transmittance Oximeter Prototype
This was the first prototype developed to demonstrate the feasibility of a pulse oximeter system. This
system is very rudimentary and used for system tests and software development.
10.2 Reflectance Oximeter Prototype
This is the main deliverable for this project. This is the combination of all of the different systems that
worked on for this project. This prototype could be taken and developed into a marketable product.
10.3 Oximeter Circuit Design
The hardware for this system has been combined into one schematic using Eagle CAD shown in the
figure below. A Gerber file circuit was then created from this file so that a fabricated circuit board could
be printed.
45
Figure 6. Oximetry Circuit
This Eagle CAD schematic was then used to create a Gerber file which could be used to fabricate printed
circuit boards of the design. This Gerber file schematic is shown in the figure below.
46
Figure 7. Oximetry Gerber file
For the prototype the hardware components have been combined onto perfboard to demonstrate this
system. The completed product is shown in the figure below.
47
Figure 8. Circuit Prototype
10.4 Oximeter Software
The software for this project was developed in python for use on a raspberry pi. The software components
included data acquisition, signal processing, oximetry, and control system modules.
10.5 Graphic User Interface
The GUI was developed in Python for use on a Raspberry pi. It was developed to provide a simple way
for the user to interact with the device to see their heart rate and blood oxygen level. The GUI was
designed to be simple and easy to operate on a touch screen device. The GUI was written in python so
that it can be easily applied to different platforms such as windows or Linux and also that it could fairly
easily be transformed into a cell phone app.
10.6 Product Concept Design
Using the approximate size of the final design circuitry if manufactured on a PCB and the sizes of other
similar devices, the team used Inventor to create a concept design of what the final product would look
like if it was developed fully and brought to market. The concept rendering can be seen in the figure
below.
48
Figure 9. Final Product Concept
11 Future work
The completion of a working reflectance oximeter prototype, complete with GUI and warning system,
means it’s time for PODS consider the next step. As the prototype was under construction, it became
obvious that controlling scope meant that PODS needed to focus on what could be done and create a list
of things to do in the future. The inspiration for the list of future work came from many sources including
product announcements, ideas from within the team and encountered problems.
If PODS were continuing work on this oximeter, a more in depth study on signal processing would need
to be conducted.
12 Conclusion
Based off of the success of the design and prototyping process, PODS sees the wrist worn pulse oximeter
as the future of pulse oximeters. Taking advantage of reflectance oximetry and the market shift away
from a traditional finger based pulse oximeter gives the product designed by PODS a unique place in the
market which will translate into a successful business. The PODS product will keep those at risk of
hypoxia safer and more comfortable than conventional products.
49
13 Acknowledgements
Team PODS would like to thank the following individuals for the contributions they made to this product.
Professor Mark Michmerhuizen
Professor Michmerhuizen is the main advisor for team 12.
Class Advisors
Professor David Wunder, Professor Ned Nielson and Professor Jeremy VanAntwerp all assisted the
team through their lectures.
Professor Brouwer
Professor Brouwer provided advice on digital systems debugging and signal processing methods.
Professor Kim
Professor Kim provided suggestions for choosing electrical component such as the type of cable to use to
connect the hardware to the microprocessor.
Industrial Consultant
Erik Walstra provided sound guidance and strategies for approaching the different aspects of this project.
50
14 References
n.d. "A Look at the Basics of Bluetooth Technology." Basics | Bluetooth Technology Website. Accessed
November 7, 2014.
n.d. "IEEE 802.11 Standards Tutorial." IEEE 802.11 Standards.
n.d. Mouser. www.mouser.com.
Newegg. n.d. Raspberry Pi B+ Broadcom.
http://www.newegg.com/Product/Product.aspx?Item=N82E16813142003&nm_mc=KNCGoogleAdwords-PC&cm_mmc=KNC-GoogleAdwords-PC-_-pla-_-Embedded+Solutions-_N82E16813142003&gclid=CNbm08us7sECFc1_MgodhnEAWg.
n.d. "Oximetry." Health Library, John Hopkins Medicine.
n.d. "Oximetry." Health Library. John Hopkins Medicine.
2014. Pilot certification in the United States. May 11. Accessed October 9, 2014.
http://en.wikipedia.org/wiki/Pilot_certification_in_the_United_States.
2014. Pulse Oximeter Market Expected to Grow to over $1.3 Billion by 2020 in the U.S., Asia Pacific,
and Europe Combined. September 15. Accessed October 2014. http://globenewswire.com/newsrelease/2014/09/15/666015/10098590/en/Pulse-Oximeter-Market-Expected-to-Grow-to-over-1-3Billion-by-2020-in-the-U-S-Asia-Pacific-and-Europe-Combined.html.
Wax, David B., Philip Rubin, and Steven Neustein. 2009. "A Comparison of Transmittance and
Reflectance Pulse Oximetry During Vascular Surgery." Anesthesia & Analgesia 109.6 1847-849.
n.d. "ZigBee Technology." ZigBee Alliance.
51
15 Appendix 1: Maxim MAX1416 Data Sheet
52
Table 22. Income Sheet
PODS
Pro-Forma Statement of Income
Year 1
Year 2
Year 3
Sales revenue
2,500,000
3,000,000
3,600,000
Variable Cost of Goods Sold
1,000,000
1,200,000
1,400,000
169,750
169,750
169,750
71,450
129,595
102,553
1,258,800
1,500,655
1,927,697
Variable Operating Costs
110,000
130,000
155,000
Fixed Operating Costs
616,250
256,000
256,000
Operating Income
532,550
1,114,655
1,516,697
92,250
166,050
129,150
Income Before Tax
440,300
948,605
1,387,547
Income tax (40%)
176,120
379,442
555,019
Net Income After Tax
264,180
569,163
832,528
Fixed Cost of Goods Sold
Depreciation
Gross Margin
Interest Expense
Table 23. Statement of Cash Flow
PODS
Pro-Forma Statement of Cash Flows
Year 1
Year 2
Year 3
-
1,730,630
2,010,388
Net Income After Tax
264,180
569,163
832,528
Depreciation expense
71,450
129,595
102,553
Invested Capital (Equity)
50,000
-
-
Increase (decrease) in borrowed funds
1,845,000
(369,000)
(369,000)
Equipment Purchases
(500,000)
(50,000)
(20,000)
Ending Cash Balance
1,730,630
Beginning Cash Balance
2,010,388
2,556,469
53
Table 24. Break Even Analysis
PODS
Break - Even Analysis
Year 1
Sales revenue
Year 2
2,500,000
Year 3
3,000,000
3,600,000
Less: Variable Costs:
Variable Cost of Goods Sold
1,000,000
1,200,000
1,400,000
Variable Operating Costs
110,000
130,000
155,000
Total Variable Costs
Contribution Margin
1,110,000
1,330,000
1,555,000
1,390,000
1,670,000
2,045,000
Less: Fixed Costs
Fixed Cost of Goods Sold
169,750
169,750
169,750
Fixed Operating Costs
616,250
256,000
256,000
Depreciation
71,450
129,595
102,553
Interest Expense
92,250
166,050
129,150
Total Fixed Costs
54
Income Before Tax
949,700
721,395
657,453
440,300
948,605
1,387,547
55
Table 25. Ratio Analysis
Year 1
Total Fixed Costs
Contribution Margin %
Break Even Sales Volume
Break Even Sales Unit Volume
Year 2
Year 3
949,700
721,395
657,453
56%
56%
57%
1,708,094
1,295,919
1,157,374
3,416.19
2,591.84
2,314.75
Equipment
Depreciation
Purchases
Equipment Purchases Year 1
500,000
Equipment Purchases Year 2
50,000
Equipment Purchases Year 3
20,000
MACRS Rates (7-year recovery period)
Year 1
Year 2
71,450
Year 3
122,450
87,450
7,145
12,245
2,858
0.1429
71,450
129,595
0.2449
0.1749
102,553
Interest Expense:
Annual interest rate on debt
10%
Year 1
Average debt balance
Interest expense
Year 2
Year 3
922,500
1,660,500
1,291,500
92,250
166,050
129,150
Ratio Analysis
Year 1
Year 2
Year 3
Gross Margin of Revenue
0.76
Profit Margin
0.11
0.19
0.23
Net Asset Turnover
2.89
1.60
1.58
Debt to Equity Ratio
37
0.59
0.63
0.55
1.19
56
Budget
Table 26. Budget
Date
Item
Quantity
Cost
Total
Beginning Balance
Balance
$500.00
Fall
ADC
1
$8.73
$8.73
$491.27
Fall
Photodiodes*
4
$1.34
$5.36
$485.91
Fall
LEDs*
4
$1.06
$4.24
$481.67
Fall
Raspberry Pi B+
1
$35.56
$35.56
$446.11
Fall
Breakout Wires
1
$3.00
$3.00
$443.11
Fall
PiTFT (Display)
1
$24.95
$24.95
$418.16
2/11/2015
ADS1015 (ADC)
1
$9.95
$9.95
$408.21
3/14/2015
MCP4725 (DAC)
2
$4.95
$9.90
$398.31
5/8/2015
Raspberry Pi 2
1
$49.00
$49.00
$349.31
5/9/2015
3D Printing (Housing)
3
$5.00
$15.00
$334.31
$165.69
$334.31
Total
57
Table 27. Work Hours Breakdown
Date:
Time
Time
Total
In:
Out:
Time:
Name:
What did you work on?
2/11/2015
2:30
3:30
1
Nick
Senior Design work day
2/11/2015
2:30
3:30
1
Taylor
Senior Design work day
2/11/2015
2:30
3:30
1
Scott
Senior Design work day
2/12/2015
11:45
1:30
1.75
Scott
Worked on test plan, team blurb
2/12/2015
11:45
1:20
1.58
Nick
Prototyping research, photodiode
2/12/2015
11:45
1:30
1.75
Taylor
Prototyping research, photodiode
2/13/2015
2:30
3:30
1
Scott
Test Plan
2/13/2015
2:30
3:30
1
Nick
Photodiode
2/18/2015
2:30
3:30
1
Scott
Test Plan, construct black box
2/19/2015
2:30
3:30
1
Taylor
Amplifier citcuit building/testing
2/19/2015
12:00
1:30
1.5
Scott
Test Plan, secure samples from OSI elctronic, fix black box
2/19/2015
11:45
1:30
1.75
Nick
Circuit
2/19/2015
11:45
1:30
1.75
Taylor
Amplifier circuit building/testing
2/25/2015
2:30
3:30
1
Scott
Test plan, organize google drive, update reference document
2/25/2015
2:30
3:30
1
Nick
Soldered ADC
2/25/2015
2:30
3:30
1
Taylor
ADC setup
2/26/2015
11:30
12:30
1
Scott
Update Reference Document, began revision of PPFS and Team
Blurb
2
Taylor
Finished setting up ADC circuit/software on the Pi
2/28/2015
1
Scott
Started Presentation, Uploaded Documents to Onedrive,
3/1/2015
1
Scott
Industrial Consultant Blurb, created some placeholders for future
2/26/2015
11:45
1:45
documentation
4/26/2015
4:00
9:00
5
Nick
Final Report
4/26/2015
7:00
10:00
3
Taylor
Final Report
4/26/2015
3:00
5:00
2
Scott
Final Report
4/27/2015
8:00
9:00
1
Nick
Final Report
4/27/2015
1:00
2:00
1
Nick
Final Report
4/27/2015
12:30
1:30
1
Taylor
Final Report
4/27/2015
3:30
5:30
2
Taylor
Final Report
4/27/2015
3:30
4:30
1
Scott
Final Report
4/28/2015
9:00
12:00
3
Nick
PyGame GUI research
4/28/2015
1:00
3:00
2
Nick
GUI/Final Report
4/28/2015
1:00
8:00
7
Taylor
Prototype Hardware Building
4/29/2015
9:00
12:00
3
Nick
GUI
4/29/2015
2:00
4:00
2
Nick
Final Poster Draft
4/29/2015
8:00
10:00
2
Nick
Final Poster Draft/ Team meeting
4/29/2015
3:00
10:00
7
Taylor
Pulse oximeter software development/Team meeting
58
4/30/2015
9:00
10:30
1.5
Nick
Final Poster Draft/ update meeting minuets
4/30/2015
2:30
3:30
1
Scott
Final Poster
4/30/2015
3:30
4:00
0.5
Scott
Final Report Draft
4/30/2015
4:00
5:00
1
Scott
Test Plan
1
Scott
Final Poster
4/30/2015
4/30/2015
11:30
2:30
3
Taylor
Testing and calibration software development/Poster
4/30/2015
7:00
11:00
4
Taylor
Poster/Product concept design
5/1/2015
3:30
6:30
3
Scott
Housing unit
2
Nick
GUI
5/1/2015
5/1/2015
1:00
1:30
0.5
Taylor
Testing and calibration software development
5/1/2015
3:30
6:30
3
Taylor
Housing unit
5/2/2015
3:30
6:30
3
Scott
Testing and calibration software development/Poster
5/2/2015
2:00
6:30
4.5
Taylor
Testing and debug
5/2/2015
8:00
1:00
4
Taylor
Testing, debug, software/filter development
5/3/2015
10:00
10:30
0.5
Scott
Research solutions to bad signal
5
Nick
GUI
5/3/2015
5/3/2015
6:30
9:30
3
Scott
Presentation, report
5/3/2015
6:00
1:00
7
Taylor
Presentation, testing, software/filter development
5/4/2015
8:30
11:15
2.75
Scott
Filter research and filter parameter testing
2
Nick
GUI
5/4/2015
5/5/2015
6:30
9:30
3
Scott
Filter parameter testing in MATLAB
5/4/2015
7:00
1:00
4
Taylor
lowpass filter testing
5/5/2015
5:00
11:00
6
Taylor
Redigned software control system, filter testing
5/5/2015
8
Nick
GUI
5/6/2015
7
Nick
GUI
5/6/2015
4
Scott
Housing unit
5/6/2015
3:30
7:30
4
Taylor
clean-up, workstation move, anti-aliasing filter
5/6/2015
9:00
11:00
2
Taylor
soldered anti-aliasing filter and tested
2
Scott
Filter testing, housing
5/5/2015
5/7/2015
9:00
12:00
3
Nick
GUI
5/8/2015
11:00
3:30
4.5
Nick
Design night prep/presentation
5/9/2015
9:00
2:00
5
Nick
Design night presentation
15
Taylor
Testing, Software Development, Debug
13
Scott
Testing, Software Development, Debug, Housing
11
Taylor
Testing, Software Development, Debug
8
Scott
Testing, Software Development, Debug, Housing
5.5
Scott
Fabricate stand for demonstration, senior design night prep, finish
5/7/2015
NA
NA
5/7/2015
5/8/2015
NA
NA
5/8/2015
5/9/2015
9:00
2:30
housing
5/9/2015
9:30
2:30
5
Taylor
Software Development, senior design night stuff
59