MOBILE PHONE PULSE OXIMETER A Thesis Presented By Paul Aaron Bohn to The Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Master of Science in the field of Electrical Engineering Northeastern University Boston, Massachusetts May 2015
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MOBILE PHONE PULSE OXIMETER
A Thesis Presented
By
Paul Aaron Bohn
to
The Department of Electrical and Computer Engineering
in partial fulfillment of the requirements for the degree of
Master of Science
in the field of
Electrical Engineering
Northeastern University Boston, Massachusetts
May 2015
iii
DEDICATION
To my wife Erin and to my family for their life long support of all my engineering endeavors.
iv
ACKNOWLEDGMENTS I would like to thank the following individuals for their support: Prof. Mark Niedre my thesis advisor for his guidance and for allowing me work independently towards mutual goals. Prof. Gunar Schirner for helping with brainstorming and providing resources to the project. J.P. Laine, my group leader at the Charles Stark Draper Laboratory, Inc., for his encouragement to continue my pursuit of education and for his constant career mentoring. Walter Foley, a colleague, for his friendship and for sharing some of the knowledge that he obtained over his forty-plus year career in engineering. Mary Beth Weissman, Elaine Arnold, and Steve Panagakos at Precision Graphics Inc. for assembling the prototype printed circuit boards. Janki Bhimani and Phanindhar Repala for their contributions towards the development of an Android application. The Senior Capstone Group consisting of Dan Thompson, Dan Abel, Dan Huehner, Hunt Graham, Portia Stephens, and Kerrianne O'Brien for continuing the project after my thesis work and taking it to the next level.
v
TABLE OF CONTENTS
LIST OF TABLES ............................................................................................................................... vii
LIST OF FIGURES ............................................................................................................................ viii
LIST OF ACRONYMS .......................................................................................................................... x
ABSTRACT ....................................................................................................................................... xii
I. SCHEMATIC ................................................................................................................................. 55
II. BILL OF MATERIALS .................................................................................................................... 60
III. PCB LAYOUTS ............................................................................................................................ 65
IV. ELECTRONICS CALCULATIONS ................................................................................................... 73
V. MATLAB SCRIPTS ........................................................................................................................ 82
VI. WORK BREAKDOWN STRUCTURE ............................................................................................. 90
VII. WORK STATUS UPDATES ....................................................................................................... 101
VIII. PART NUMBERING SYSTEM .................................................................................................. 119
ABOUT THE AUTHOR.................................................................................................................... 121
vii
LIST OF TABLES Table 1: General Design Goals ........................................................................................................ 6
Table 2: Specific Design Goals ........................................................................................................ 8
Figure 39: IR Ambient Subtraction Before Filter (red); After Filter (blue) from Testbed ............ 50
Figure 40: Android Application Hardware Demo by Undergraduate Capstone Team .................. 51
x
LIST OF ACRONYMS ADC Analog to Digital Converter
AFE Analog Front-End
AGC Automatic Gain Control
COTS Commercial off-the-shelf
CS Chip Select
CSV Comma separated values
DAC Digital to Analog Converter
ECG Electrocardiogram
GPIO General Purpose Input Output
GUI Graphical User Interface
HR Heart Rate
Hb Deoxyhemoglobin
HbO2 Oxyhemoglobin
LED Light Emitting Diode
MCU Microcontroller Unit
MISO Master Input Slave Output
MOSI Master Output Slave Input
NIR Near Infrared
PC Personal Computer
PCB Printed Circuit Board
Pleth Photoplethysmogram
Pox Pulse Oximeter
PR Pulse Rate
SCLK Serial Clock
SpO2 Blood Oxygen Saturation
SPI Serial Peripheral Interface Bus
SNR Signal-to-noise Ratio
xi
TIA Transimpedance Amplifier
USB Universal Serial Bus
xii
ABSTRACT
There is global demand for low cost medical care diagnostics, and too often these life-saving tools are unavailable to low-income countries and remote areas of the world. One example of such a device is a pulse oximeter: a vital instrument that measures blood oxygen saturation. A modern medical grade pulse oximeter is often physically large and requires training and access to a mains power. All such points are contrary to operation in a remote low-income locale. This project covers the design, fabrication, and testing of a testbed pulse oximeter that is targeted for use in the developing world. While developing areas may be lacking infrastructure, mobile phones are readily available. Mobile phones provide a source of power, computation, and access to information that was previously unavailable. By connecting through the headset jack, the testbed design utilizes the phone’s capabilities run a pulse oximeter. Data was acquired from the testbed and then analyzed with good results. Global access to point-of-care medical devices can be significantly improved with further use of mobile computing. This will lead to reductions in cost, increased portability, improved patient compliance, and expanded distribution of medical knowledge.
1
CHAPTER 1: INTRODUCTION
1.1 Overview
The objectives of the thesis are to i) create a record of a testbed pulse oximeter design
that is targeted for use in the developing world, ii) to freely distribute the design information, and
iii) to transfer the knowledge to the Northeastern University student body to continue the work.
1.2 Intro to Pulse Oximetry
A pulse oximeter is a device that measures blood oxygen saturation (SpO2) and pulse rate
(PR) which are important indicators of health. All organs need oxygen to function properly;
performing simple cognitive tasks becomes challenging within minutes after a loss of oxygen.
The heart and brain are particularly sensitive to a reduction in oxygen, and when those organs
begin to fail, risk of death rises dramatically (World Health Organization, 2011). The use of pulse
oximeters can greatly reduce the risk of death during medical procedures that require general
anaesthesia by monitoring a patient's blood oxygen level and intervening when the oxygen drops
below an acceptable range (World Health Organization, 2011).
A pulse oximeter indirectly measures blood oxygen saturation by gauging the color
intensity of blood (Texas Instruments, 2013). Color is an indicator of the amount of oxygen that is
in blood. Red blood cells contain a protein molecule called hemoglobin that transports oxygen
(World Health Organization, 2011). There are two types of hemoglobin: oxyhemoglobin is
hemoglobin combined with oxygen, and deoxyhemoglobin is hemoglobin that lacks oxygen.
Blood transports oxygen from the lungs and heart to the extremities where it is released into
tissues. In a cyclical fashion, oxygen lacking blood returns to the heart and lungs to be
oxygenated. Blood rich with oxyhemoglobin appears red because it filters most light from the
visual spectrum except for red light. The dashed line in figure 1 represents the light absorption of
oxyhemoglobin. The line sharply dips near the red (~660nm) portion of the visual spectrum; thus,
allowing red light to transmit and scatter through the blood. The solid line in figure 1 represents
the light absorption of deoxyhemoglobin (Hb). At the red wavelength of 660nm the
deoxyhemoglobin (Hb) absorption is much greater than oxyhemoglobin (HbO2). The additional
2
attenuation of light from the lower concentration of oxygen causes blood to become dark blue in
color. This explains why the skin of somebody who stops breathing starts to appear blue.
Pulse oximeters typically measure blood color intensity at two different wavelengths of
light- red and near-infrared (Texas Instruments, 2013). These wavelengths are chosen for their
light transmission characteristics through biological tissue. The common finger-clip pulse
oximeters use two LEDs one for each wavelength and a photodetector in a transmissive
arrangement. The LEDs are on located on one side of the finger while the photodetector is located
on the other side such that light is transmitted through the tissue during operation.
Figure 1: Molar Extinction Coefficient for Hemoglobin in Water vs. Wavelength
The concentration of oxy- and deoxyhemoglobin can be estimated with knowledge of the
absorption coefficients at two wavelengths (Wang & Wu, 2007). “The absorption coefficient is
defined as the probability of photon absorption in a medium per unit path length” (Wang & Wu,
3
2007). Figure 1 has two vertical lines that intersect with the molar extinction coefficient curves.
One vertical line is at a wavelength of 660nm (red) and another at 895nm (NIR). An absorption
coefficient equation can be written for each of the wavelengths (Wang & Wu, 2007). The
equations are in terms of wavelength molar extinction coefficients and molar concentration of
oxy- and deoxyhemoglobin (Wang & Wu, 2007). The two equations make up a system with two
unknowns variables. Once oxy- and deoxyhemoglobin is determined. Blood oxygen saturation
can be calculated by taking the ratio oxyhemoglobin to the total hemoglobin in the blood (Wang
& Wu, 2007).
Pulse oximeters often display blood volumetric pulse waveform over time, and report
pulse rate in beats per minute. This is called a pleth waveform, which is shorthand for
photoplethysmogram. The changing blood volume is determined by shining light through tissue
while sensing the returning light with a photodetector. Some of the light will be absorbed in a
periodic fashion as blood pulsates through the body causing a fluctuation in light intensity. The
pulsation of light is sensed by the photodetector then recorded and displayed by the device. The
device then calculates pulse rate by monitoring the number of pulses that occurred in a given
time.
Most pulse oximeters determine SpO2 from an empirical formula (Texas Instruments,
2013). First, the red and IR signals are normalized to remove the DC component caused by
biological tissue and bone. Second, a ratio of the red-IR normalized signals is taken. Third, a
calibration offset and scale factor is applied to the red-IR ratio to generate the resultant SpO2.
The scale factor and offset is empirically determined through calibration and is often stored in a
lookup table.
1.3 Low Cost P-Ox for the Developing World
In the developing world, there is a great need for low-cost point-of-care medical devices
such as pulse oximeters. The lack of infrastructure, reliable source of power, transportation, and
well trained medical workers makes it difficult, if not impossible, to deploy medical equipment
designed to operate in stable hospital conditions. Limited access to medical devices \in low-
income countries leads to lesser quality of life and shortened life spans.
[For example], children with very severe or severe pneumonia should usually be
treated in hospital, but many low-income and middle-income countries do not have a
sufficient number of hospital beds for this strategy. . . .
4
If pneumonia is combined with hypoxaemia, as happens in 13% of cases, children
are five-times more likely to die than are those with only pneumonia. Oxygen
concentrations should therefore be monitored and oxygen therapy should be made
available, but this approach is not always possible. Low-income and middle-income
countries need an estimated 1,000,000 pulse oximeters. (Howitt, et al., 2012)
Affordability of medical devices is of concern. Medical grade pulse oximeters can cost
hundreds or even thousands of US dollars. Low grade devices can be purchased for around 20 US
dollars, but may not meet medical standards or may not come with needed features for use in a
low income situation. Market analysis is required to obtain a true target cost that is viable for low-
income countries. One could imagine a scenario where some of the cost could be offset through
philanthropic means.
1.4 Proposed / Design
The testbed pulse oximeter design outlined in this thesis showcases an example of a
mobile phone turning it into a medical device. Mobile phones have many desirable characteristics
that make them well suited for the task. For example, they are readily available throughout the
world. As of May 2014, there were nearly seven billion mobile subscriptions worldwide
(MOBITHINKING, 2014). 5.4 billion of those subscribers are in the developing countries with a
90.2% market penetration (MOBITHINKING, 2014). Phones provide a reliable source of power.
This is directly achievable by harvesting energy from the phone. Indirectly, the phone’s charger
or a spare battery pack can serve as a power source. Mobile phones have ample computational
power and storage for many medical diagnostic applications. Mobile phones can provide an
avenue for telemedicine by storing data and sending diagnostic results to trained clinicians for
analysis and monitoring. Finally, phones can run applications to guide untrained users. These
applications can provide real-time feedback, medical advice, and operator instructions.
The audio headset jack offers a path to interface medical devices with a mobile phone
(Kuo, Verma, Schmid, & Dutta, 2010). University of Michigan’s Hijack project demonstrated
that data and power can be transferred over the common headset jack opening a method to
connect sensors to existing mobile phones. Drawing power from the headset jack eliminates the
need for batteries or alternate power sources thus keeping cost, size, and weight down. It reduces
the logistical need for batteries to keep the devices operating. Sending diagnostic results through
the audio headset jack forgoes the need for a proprietary data communication port. Almost all
5
mobile phones have a headset jack so it can serve a near universal solution for transmitting low
bandwidth data to a mobile phone. In addition, a modular platform could be developed around the
headset jack interface to add other sensor modalities such as EKG, temperature, blood pressure,
etc. (Kuo, Verma, Schmid, & Dutta, 2010). The remainder of this document addresses design
approaches for the development of a testbed pulse oximeter that is powered by and sends data
through a mobile phone audio headset jack.
1.5 Candidates Contribution
The effort to develop a pulse oximeter testbed was led by the thesis candidate and this
involved the management of fellow students. A summary of work for this project included: (1)
literature research and a design trade study, (2) electronics design and layout of two custom
circuit boards: a mobile phone audio breakout board test fixture and a testbed for pulse oximetry,
(3) the assembly of three breakout boards, (4) managed vendors and manufacturers for test
equipment, parts procurement, PCB manufacturing, and assembly work, (5) wrote MCU test
software in C language and analysis software in MATLAB, (6) wrote thorough technical and
programmatic documentation, (7) tested the hardware, (8) turned over a working example to a
Northeastern University undergraduate capstone group for future improvements.
6
CHAPTER 2: SYSTEM DESIGN
The pulse oximeter system design takes into account the unique environment, use cases,
and constraints presented with a design for the developing world. This chapter covers: (1) general
and specific design goals that were derived from an initial needs assessment, (2) several design
approaches that were considered, (3) a system architecture and behavioral model.
2.1 Design Goals
The needs assessment and design goals that are listed in tables 1 and 2 are forward
looking with the intention that the testbed described in this thesis will make an incremental step
towards meeting the goals listed in this chapter.
General Design Goals
Description
Public Acceptance ● The device must be accepted by users and medical providers of the developing world.
Safety ● The device must pose a very small safety risk to the users. This includes the use of non-hazardous materials/coatings, no choking hazards, no cutting hazards, no electrical hazards, etc.
Reliable ● The device must be very reliable during product lifetime and during operation.
Ease of Operation ● The device must be easily setup. This includes the uses of hardware and software
● The device will display user instructions in real-time.
Performance ● The device must operate in accordance with industry standards for pulse oximetry.
● The device may not perform at the same standards as a high-end medical device in favor for power savings, cost minimization, public acceptance, and ease of operation.
Table 1: General Design Goals
7
General Design Goals
Description
Minimum Cost ● The final price of the device must be affordable to medical providers in low income countries.
Minimum Cost ● The final price of the device must be affordable to medical providers in low income countries.
Use of Standard Parts ● The device will incorporate commercial-off-the-shelf (COTS) electronics and mechanical components to minimize cost.
Ease of Construction ● The device will have minimal physical parts to simplify construction.
● The device will be designed to demonstrate a path for high volume manufacturing.
● The device will be disassemblable.
Minimum Maintenance and Ease of Maintenance
● The device will require light cleaning after each use. ● Design cost minimization will be weighted heavier than ease
of maintenance. ● The device will run self-diagnostics to determine if it is
operating within specifications. If it detects that it is not operating within specifications, it will deactivate and provide user feedback.
Reconfigurable ● The device will work with a broad range of mobile devices. ● The device will work with adults, children, and infants. ● The device itself will not be reconfigurable in favor of cost
minimization, ease of use, ease of construction, ease of maintenance.
Durability ● The device will be ruggedized for field use. ○ The device will handle repeated drops from 2 meters
off the ground onto solid pavement. ○ The device will be liquid resistant.
● The device will operate in environmental conditions unique to its operating locale.
Environmental Protection
● The device should be fully recyclable. ● Should minimize the use of materials and energy to construct
the device. ○ Low SWaP (size weight and power)
● The device should have minimal toxic materials.
Table 1: General Design Goals Continued
8
Specific Design Goals
Description
Physical ● Finger size form factor ● Incorporate finger sensor (photodetector and LEDs) into device ● Robust cabling
Functional ● Must operate for the duration of a surgical procedure ● Audible feedback ● Alarm modes
○ High PR ○ Low PR ○ No PR ○ Desaturation
● Will operate in low power mode ○ Detect inactivity
● Will harvest energy from phone ● Compatible with as many mobile phones as possible ● Telemedicine ● Provide real-time help ● Bidirectional data transmission over mobile phone headset jack
Environmental ● Regional operating requirements
Economic ● Quantities in the thousands to hundred thousands
Legal ● Must meet most medical regulatory requirements as long as they do not interfere with high-level goals
● Open intellectual property ● Open source hardware and software
Human Factors & Ergonomics
● Compatible with adults and children
Table 2: Specific Design Goals
9
2.2 System Architecture
At the top level the system is comprised of a mobile phone and a pulse oximeter device.
The next layer down includes the components that make up the phone and the pulse oximeter
device. The final layer is made up of the software that runs on both devices.
Several design approaches and architectures were considered for the pulse oximeter
device. The design goal to reduce the overall system cost led to some ideas to use the mobile
phone’s audio circuitry to directly drive the pulse oximeter functionality with minimal
components. This approach would reduce the universality of the solution by limiting the different
types of phones that would work with the device. The pleth measurement performance would also
vary with the phone type.
Another approach was to design the pulse oximeter device circuitry using discrete
electronic components. This is certainly a valid approach that could be cost-effective depending
on parts selection. The disadvantages of this choice include an increase in the number of parts and
a modest increase in physical volume and complexity.
The approach that was selected for this thesis work included the use of a purpose-built
integrated circuit for pulse oximetry. This approach offers several advantages: increased pleth
measurement performance, a reduction in parts count, increased manufacturability, and the cost
drops significantly with volume. The disadvantages might include: a reliance on a single vendor
for the integrated circuit, and the unit cost for small production quantities. As of April 2015, the
current price for 2500 pieces of Texas Instruments part number AFE4490RHAR is 8.94 USD.
While the price may seem a little high, and it may be considered to be a disadvantage it is worth
mentioning that AFE4490 is a medical grade part that can be found in high end instruments. Also,
high production volume will offer a reduction in price and it is likely a business arrangement
could be made with Texas Instruments that would further the cause.
10
Tables 3 and 4 list the pulse oximeter device and mobile phone components for the
selected design approach.
Pulse Oximeter Component
Subcomponents Description
Printed Circuit Board
Photodetector, IR LED, & red LED Sensor probe
Analog front-end for pulse oximetry Detector, LED illumination, signal
digitization, and timing electronics
Microcontroller Provides SpO2 calculation, analog
front-end control, and serial data
communication
Power management electronics Power harvesting, regulation, &
storage
Enclosure Probe/Sensor Fixture Mechanical enclosure features that
holds LEDs and photodiodes
Finger Clip Hinge mechanism and enclosure
body
Data & Power Interface Cable Assembly
Shielded four conductor cable Cable assembly connects the mobile
phone to the pulse oximeter 3.5mm audio connector
Table 3: Pulse Oximeter Device Components
11
Mobile Phone Component
Description
Processor Provides computation power to process and display data.
Memory Provides data storage.
Display Provides graphical user interface.
Speakers Provides audible feedback to the user.
Data & Power Interface Audio jack provides data and power interface.
Radios Provides access to the internet and remote monitoring station.
Battery / Power Pack Provides power through an internal mobile phone battery or an external power pack.
Charger Mobile phone charger that can be solar, thermal or a standard wall adapter.
Table 4: Mobile Phone Components
Figure 2 System Diagram shows interconnect between electronic components. This
includes the communications between the analog-front end, MCU and phone. The diagram shows
a phone’s right audio channel supplying the power management block with a power signal. The
power management block supplies power to the MCU and phone while the MCU has some
control authority over the power management block.
12
Figure 2: System Diagram
13
2.3 System Behavior
Much of the system behavior is defined by the device code. The code will include an
Android mobile phone application for user interface and microcontroller code for hardware
management.
2.3.1 MCU
The microcontroller firmware will have many components; most of which are shown in
Figure 3 MCU Firmware Component Diagram. There will be an initialization routine that occurs
during power up plus components for power management, diagnostics, and debugging. There will
also be two control loops: the first is for ambient light cancellation, the second is for automatic
gain control and LED output. There will be routines for calculating SpO2 and pulse rate (PR).
The SpO2 calibration data will be stored in MCU memory. The MCU will handle
communications between the AFE4490 analog front-end for pulse oximetry and the mobile
phone.
Figure 3: MCU Firmware Component Diagram
14
On power up, the MCU will initialize chip settings, GPIO pin settings, USART,
interrupts, etc. It will enable the primary LED voltage regulator, and then it will send the default
settings to the analog front-end. The MCU will handle the power management, sequencing, and
monitoring. It will report diagnostic values from the analog front-end and error states to the
mobile phone. Debugging code will be embedded for testing communications and test modes of
operation.
A minimum of two control loops are needed for the device to operate in a dynamic
environment. One control loop will be used for ambient light cancellation. The other control loop
will be used to automatically adjust LED current levels and amplifier gain settings. The ambient
light cancellation loop will input ambient data from the analog front-end then estimate the
ambient value to be cancelled. Finally it will adjust the cancellation current by digitally
controlling the ambient-cancellation DAC (Texas Instruments, 2014). The loop adjusts the dc-
biased signal coming from the photodiode I-V amplifier to the midpoint value of the second gain
stage amplifier (Texas Instruments, 2014). The automatic gain control (AGC) loop adjusts the
amplifier gain settings and the LED current levels to maximize the signal-to-noise ratio (SNR)
while limiting power consumption to the available energy capacity. An additional power
optimization control loop could be implemented that would change the measurement duty cycle
and current levels to meet power consumption needs.
Data communication to and from the analog front-end will be accomplished through
serial peripheral interface (SPI) bus. The microcontroller comes with an SPI hardware peripheral
that is controlled by setting MCU registers. An SPI library with functions for initialization,
reading, and writing registers will be used in the main program. The mobile phone data
communications will be sent over the phone’s headset jack by AC-coupling audio signals to
microcontroller GPIO pins. The headset jack audio signals will contain Manchester coded binary
data. The microphone channel will handle the transmission of data to the phone, and the left
stereo channel will be used to receive data from the phone. A library of interrupt driven functions
will be used for the phone audio communications.
2.3.2 Mobile Phone Application
The mobile phone Android application will contain the following components: a
graphical user interface (GUI), a real-time user help module, an alarm handler, an audible pulsed
tone generator, an audio data communication interface, a sinewave generator for device power, a
data logger, a cloud server internet client, and device communication debugging interface. Figure
4 Mobile Phone Functional Diagram details some of these components.
15
Figure 4: Mobile Phone Functional Diagram with Android Application Components
The GUI will provide easy-to-understand instructions to an unfamiliar user. The device
interface will be similar to professional medical grade instruments in the operating room, so that
trained medical staff will be comfortable utilizing the device. After launching the Android
application the user will be presented with graphical instructions that explain the setup of the
device. Figure 5 Pictorial Start-Up Instructions is an example series of screens that could be
displayed to a user.
16
Figure 5: Pictorial Start-Up Instructions
First the device must be plugged in, and then the Android application will generate a sine
wave audio signal on the right audio channel to power the device. Adjusting the mobile phone
volume to maximum provides the most energy to the device. After the device initializes, the
mobile phone application will initiate communications with the device over the left audio channel
and mic channel. After communications with the device is established, the main screen will
appear. If any error states exist the user will be presented with graphical instructions on how to
correct the problem. Figure 6 shows four example Android application screenshots. The two
rightmost images are concepts created with Google Draw, and the two leftmost images are
screenshots from an early Android GUI prototype application.
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PREL
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100
VII. WORK STATUS UPDATES
101
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
09/7/2014 03/31/2015 Paul Bohn
● Worked on thesis document 08/31/2014 09/06/2014 Paul Bohn
● Distributed information to capstone team members ● Wrote short tutorial on how to load mcu project code ● Worked on thesis document
08/24/2014 08/30/2014 Paul Bohn
● Met with Mark Niedre to discuss progress ● Collected a lot data ● Created slideshow with latest results
○ figured out register settings for AFE4490 ● Attended telecon with capstone group
08/17/2014 08/23/2014 Paul Bohn
● Identified schematic error ○ On board photodiode pinout is reversed ○ Modified custom PCB to fix photodiode pin reversal
● Updated schematic ● MCU Code
○ Added diagnostic code ○ Changed power up sequence
08/10/2014 08/16/2014 Paul Bohn
● Successfully powered up custom device (LED lights up and ADC samples) and
1 of 18 10003001
102
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
captured real data for the first time! ● Offered to provide a bare PCB to capstone team members for hardware development
testing ● Provided capstone team members with a list of task options that would drive to project
forward ● Suggested that capstone team members should call me on the phone so I can help
them with task planning ● MCU Code
○ Configured/wrote default register settings into AFE4490 ○ Refined AFE4490 register settings and added comments ○ Fixed gpio pin assignment errors ○ Setup pin interrupt service to capture data when ADC_RDY signal goes high
● Shared MCU code with capstone group 08/03/2014 08/09/2014 Paul Bohn
● Completed preliminary MCU SPI code to read and write AFE4490 registers ○ Successfully wrote registers to custom board
● Attempted to coordinate meeting with capstone team members 07/27/2014 08/02/2014 Paul Bohn
● Completed the development of a MATLAB script that will import a binary file containing raw AFE4400 SPI data into the workspace. The script parses the raw data into matrices that correspond to AFE4400 registers. The data was captured with a Total Phase Beagle SPI protocol analyzer.
● Processed the imported raw SPI data with analysis script pox.m ● Removed power to ground short on second custom PCB by cutting trace away ● Tested power supplies on second custom PCB
○ The board comes up fine 07/20/2014 07/26/2014 Paul Bohn
● Developing a MATLAB script that will import RAW AFE4400 data from a SPI protocol
2 of 18 10003001
103
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
analyzer 07/13/2014 07/19/2014 Paul Bohn
● Released preliminary MATLAB script for analyzing RAW AFE4400 data ● Communicated with Dan Thompson via email. Pointed him towards information that is
pertinent to MCU cell phone communication. ● Developing a MATLAB script that will import RAW AFE4400 data from a SPI protocol
analyzer 07/06/2014 07/12/2014 Paul Bohn
● Developing MATLAB script pox.m to analyze RAW AFE4400 data 06/29/2014 07/05/2014 Paul Bohn
● Developing MATLAB script to analyze RAW AFE4400 data ○ Able to calculate rough SPO2 values
06/22/2014 06/28/2014 Paul Bohn
● Completed SPI data capture slide show ● Developing MATLAB script to analyze RAW AFE4400 data
06/15/2014 06/21/2014 Paul Bohn
● Provided cost estimate information ● Created SPI data capture slide show
3 of 18 10003001
104
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
06/08/2014 06/14/2014 Paul Bohn
● Added SPI code to project directory ● On campus meeting
○ Turned over hardware to capstone team ● Started work to grab SPI data from development board (requires hardware mod)
05/01/2014 06/07/2014 Paul Bohn
● Installed LEDs on development boards ● Development of SPI MCU code
05/25/2014 05/31/2014 Paul Bohn
● Bringing capstone team uptospeed by distributing project information ● Development of SPI MCU code
05/18/2014 05/24/2014 Paul Bohn
● Updated the 10100001_RevA_PhonePulseOx_Development_Plan ● Met with capstone team ● Bringing capstone team uptospeed by distributing project information ● Contacted Chris Poling from ProTEQ Solutions to get a loaner Oscilloscope
05/11/2014 05/17/2014 Paul Bohn
● Updated the 10100001_RevA_PhonePulseOx_Development_Plan ● Met with Gunar and Mark to discuss project and how to bring in capstone group ● Going through MCU training material
● Located Totalphase SPI debugger cable ● Consolidated all project parts and equipment ● Requested assistance to build a future team to complete the project
● Submitted solder paste gerber file to assembly house ● Supported board assembly by answering questions ● Attended Monday team meeting ● Received boards on Friday (3/28) ● Started testing board
○ identified and fixed minor layout error ○ voltage regulators power up and adjust ○ confirmed device can be powered by a cell phone
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
Paul Bohn ● Packaged and edited PCB design files for archival ● Put parts kit together ● Shipped parts kit to assembly house ● Researched DXF to Gerber file conversion so a so a solder paste stencil can be made ● Generated a solder paste gerber file from a dxf file using linkcad7 and gerbv ● Attended Monday team meeting ● Met with Prof. Mark Niedre to give a status update
03/09/2014 03/15/2014 Paul Bohn
● Purchased Gerber Files ● PCBs arrived ● Newark parts arrived ● Digikey parts should arrive early next week ● Attended Monday team meeting
03/02/2014 03/08/2014 Paul Bohn
● Submitted Digikey order (Web ID 49783172 Access ID 76224) ● Updated 10900001_RevA_PhonePulseOx_Part_Numbering ● Submitted Newark Electronics order ● Submitted ExpressPCB order
02/23/2014 03/01/2014 Paul Bohn
● Completed PCB Layout ● Updated schematic, BOM, and Digikey order (Web ID 49783172 Access ID 76224) ● Sent design to a very experienced electrical engineer for review ● Requested quote from assembly house and worked out a deal for free assembly
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
● Attended Monday team meeting 02/16/2014 02/22/2014 Paul Bohn
● Sent information to Janki on PCB design ● Routing PCB ● Updated schematic, BOM, and Digikey order
02/09/2014 02/15/2014 Paul Bohn
● Attended Monday team meeting ● Did a factory restore on Janki’s new laptop ● Made PCB footprint ● Modified schematic ● Completed rough PCB parts placement ● Worked on Digikey order. It is basically complete at this point. ● Requested information from OSI Optics ● Started team building and recruitment
○ Identified four potential team members ● Started routing PCB
8 of 18 10003001
109
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
01/26/2014 02/01/2014 Paul Bohn
● Worked on proposal text ● Received budgetary pricing for Fluke Spo2 device $2000.00 ● Worked on design description write up ● Met with Coilcraft sales engineer. Can get any number of free samples. Modified and
custom inductor designs are possible ● Met with Janki and discussed cell phone app. Started to development of app behavior
model ● Researched Android market penetration in the developing world
01/19/2014 01/25/2014 Paul Bohn
● Wrote draft proposal text ● Updated work breakdown structure and budget ● Worked on design description write up ● Request quote for SPO2 tester ● Supported Tier1 seed grant proposal preparations
01/12/2014 01/18/2014 Paul Bohn
● Worked on pcb footprints ● Updated BOM ● Requested information from new NEU group “ENABLE” ● NEU campus meeting ● Created a Google Drive tutorial ● Developed strawman proposal document ● Created proposal budget ● Encouraged Janki to balance spring14 schedule to make time for this project
01/05/2014 01/11/2014 Paul Bohn
10 of 18 10003001
110
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
● Worked on pcb footprints ● Started digikey order: Web ID 49783172 Access ID 76224 ● Updated BOM
12/29/2013 01/04/2014 Paul Bohn
● Parts from TI have arrived ● Consolidated parts to one box ● Worked on pcb footprints ● Updated BOM
12/22/2013 12/28/2013 Paul Bohn
● Parts came in from OSI Optoelectronics ● Parts from TI have shipped
○ Went with AFE4490 because AFE4400 was backordered 12/15/2013 12/21/2013 Paul Bohn
● Updated 10303001_RevA_PhonePulseOx_Main_Board_BOM to include part package dimensions
● Making PCB footprints for the circuit board layout ● Requested samples from Texas Instruments and OSI Optoelectronics
12/08/2013 12/14/2013 Paul Bohn
● Updated 10303001_RevA_PhonePulseOx_Main_Board_BOM to include PCB footprints
● Making PCB footprints for the circuit board layout
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
● Researched Design Spark CAD tools for next version ○ http://www.designspark.com/
Mark Nakib
● Returned Analog Discovery to Ufuk Muncuk 12/01/2013 12/07/2013 Paul Bohn
● Worked on schematic and submitted draft for review ● Updated 10303001_RevA_PhonePulseOx_Main_Board_BOM ● Making PCB footprints for the circuit board layout ● Started designing an integrated PCB sensor ● Secured samples from
○ Coilcraft ○ Linear Technology
● Parts from OSI Optoelectronics are being shipped from overseas ● Attended meeting at NEU
11/24/2013 11/30/2013 Paul Bohn
● Worked on schematic and power calculations ○ Schematic is close to completion
● Requested samples from ○ Coilcraft ○ OSI Optoelectronics ○ Linear Technology ○ Silicon Labs
● Contacted Fluke medical and Silicon Labs ● Updated Google Doc 10101001_RevA_PhonePulseOx_Documentation ● Organized project directory ● Installed Google Drive for PC to streamline workflow
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
● Watched WHO pulse ox training video ● Worked on schematic and bill of materials for main board ● Created main board calculations spreadsheet ● Organized project folder and added documentation ● Applied part numbers to project files ● Design research
○ Selected parts ○ Read datasheets ○ Reviewed reference designs ○ Reviewed reference material ○ Reviewed code
Janki Bhimani
● Did reverse engineering and to the operation algorithm from code of AFE4400 ● found on which formulae it works ● traced the algorithm of operation
11/10/2013 11/16/2013 Paul Bohn
● Worked on development plan slideshow ● Made some mobile phone cartoons for slideshow ● Updated part numbering for documentation ● Capturing schematic for main PCB ● Absorbing training material created by the World Health Organization
Mark Nakib
● Installed analog discovery software ● Began experimenting to become more familiar with system
11/03/2013 11/09/2013 Paul Bohn
● Made another pass at WBS task details ● Worked on development plan slide show ● Updated audio breakout board documentation
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
● Committed audio breakout board to SVN ● Tracked down analog discovery ADI module ● Added a mobile phone study section to PhonePulseOx_Documentation ● Performed design research
Mark Nakib
● Picked up analog discovery 10/27/2013 11/02/2013 Paul Bohn
● Started a development plan slide show ● Installed TI AFE4400 development kit GUI ● Updated phone audio breakout BOM ● Assembled and tested 3 phone audio breakout boards ● Delivered phone audio breakout boards to NEU ● Updated file directory structure readme ● Created budget tracking spreadsheet ● Created configuration management part number assignment spreadsheet
Mark Nakib
● Met with Paul to pick up audio breakout boards 10/20/2013 10/26/2013 Paul Bohn
● Researched Silicon Labs Gecko MCU families ● Worked on schematic capture for cell phone pulse oximeter ● Updated nuForge wikipages ● Updated Phone Pulse Oximeter Google Document with design requirements ● Made first cut at an action item list ● Installed TortoiseSVN ● Research version control methods ● Status update meeting with Mark Niedre ● Started development of a work breakdown structure
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
● Retrieved dev kit from Mark Nidre ● Installed TI AFE4400 development kit GUI ● Experimented with TI AFE4400 development kit
Mark Nakib
● Researched mobile phone sinewave generator applications ● Requested source code for mobile phone application software ● Researched mobile phone software development
10/13/2013 10/19/2013 Paul Bohn
● Released first version of system block diagram ● Submitted project background reading material to team members ● Created project action item list ● Created instructions to submit ExpressPCB order ● Met with Janki and divided up tasks ● Started schematic capture for cell phone pulse oximeter ● Researched Silicon Labs Gecko MCU families ● Updated nuForge wikipages ● Updated Phone Pulse Oximeter Google Document
10/06/2013 10/12/2013 Paul Bohn
● Completed cell phone audio breakout board PCB layout and documentation ● Submitted breakout board design for review ● Made PCB footprint for AFE4400 ● Reviewed development board schematic ● Started to develop system block diagram
9/29/2013 10/05/2013
15 of 18 10003001
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Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
Paul Bohn
● Completed a detailed read of AFE4400 datasheet ● Completed detailed read of AFE4400 development kit user guide ● Evaluated DesignSpark CAD tools as a possible longer term solution ● Installed and used PCB Library Expert 2013 to aid layout
9/22/2013 9/28/2013 Paul Bohn
● Started to layout PCB for cell phone audio breakout board ○ using express pcb for design (http://www.expresspcb.com/)
● Met with PI on 9/23 to discuss embedded design ● Submitted items for purchasing ● Started reading AFE4400 datasheet ● Started to record design goals in design documentation
9/15/2013 9/21/2013 Paul Bohn
● Performed some design research ● Started development of a cell phone audio breakout test fixture
○ captured schematic ● Created bill of materials for audio breakout test fixture ● First parts arrived on 9/17 from allheart second order came in on 9/20 ● Started to take a closer look at the TI AFE4400 ● Read a paper AudioDAQ: Turning the Mobile Phone's Ubiquitous Headset Port into a
Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
● Gathered costing information for dev kits and parts ○ https://docs.google.com/spreadsheet/ccc?key=0Ag57FuC6l3MXdHFpSEZOSG
hUZnU1M3BYSXp4M2JtbVE#gid=0 ● Decided to develop the following as intermediate steps
○ Cell phone audio jack interface test fixture ○ Digital Stethoscope
● Purchased parts from medical supplier allheart
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Mobile Phone Pulse Oximeter Project Status Updates
Northeastern University
9/1/20123 9/7/2013
● Performed some design research ● Learned about mobile phone capabilities ● Read about hijack project (paper)
○ http://web.eecs.umich.edu/~prabal/projects/hijack/ 7/27/2013 8/31/2013 Paul Bohn
● Met with PI on 8/1 and 8/28 ● Project Research and Design Ideas ● Researched PAT instrumentation ● Read “Technologies Global Health.” and many app notes on pulse ox