Traumatic Brain Injury Eyewear (TB-Eye)
ECE4007 Senior Design Project
Section L03 TB-Eye Team
Project Advisor, Erick Maxwell
Matt Vildzius, Team Leader
Todd Biesiadecki
Matthew C Campbell
Submitted December 16, 2011
Table of Contents
Executive Summary ......................................................................................................... iii
1. Introduction ..................................................................................................................1
1.1
1.2
Objective .............................................................................................................1
Motivation ...........................................................................................................2
2. Project Description and Goals ....................................................................................2
3. Technical Specification ................................................................................................3
4. Design Approach and Details ......................................................................................4
4.1
4.2
Design Approach ..................................................................................................4
Codes and Standards .............................................................................................9
5. Schedule, Tasks, and Milestones...............................................................................10
6. Results and Acceptance Testing ...............................................................................10
7. Budget and Cost Analysis ..........................................................................................11
8. Conclusion and Future Work ...................................................................................12
9. References ...................................................................................................................13
Appendix A .......................................................................................................................15
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Executive Summary
The team has used $234 to build a prototype of the TB-Eye Traumatic Brain Injury (TBI)
monitoring device. The device monitors the acceleration of the wearer’s head caused by an
impact force and uses colored lights to notify him or her if he or she needs medical attention. The
intended market for the TB-Eye system is athletes who are at a significant risk of TBI, including
skiers, snowboarders, and cyclists. No inexpensive, lightweight, and adaptable TBI monitoring
systems are currently on the market. Systems currently available, such as Riddell’s Revolution IQ
HITS football helmet, are expensive and are designed specifically for one sport [1]. The objective
is to create a small, light-weight, battery powered device that attaches to the frame of a pair of
sunglasses. The device uses a three axis accelerometer to monitor the acceleration of the wearer’s
head caused by an impact force and uses colored lights to notify him or her if he or she needs
medical attention. Data from an impact is stored in memory on the TB-Eye monitor and a coach
or doctor may wirelessly download the recorded data to a computer and use the Graphical User
Interface (GUI) for the device to assess the risk of injury and determine what treatment is
required. The project will be tested by impacting a simulated head wearing the device. It will be
shown that the device accurately records the impact, alerts the wearer, and transmits the data to a
PC in range. The total cost of equipment is approximately $234. The outcome of the project is a
functioning prototype of the TB-Eye device.
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Traumatic Brain Injury Eyewear (TB-Eye)
1.
Introduction
The team has used $234.00 to build a prototype of the Traumatic Brain Injury Eyewear (TB-Eye)
device for athletes to wear to detect if they experience an impact to the head that may result in traumatic
brain injury (TBI). The device attaches to the frame of a pair of sunglasses that may be worn for sports
such as cycling or skiing where impacts to the head caused by falls or collisions are possible. The device
monitors the acceleration of the wearer’s head caused by an impact force and uses colored lights to notify
him or her if he or she needs medical attention. Data from an impact is stored in memory on the TB-Eye
monitor and a coach or doctor may wirelessly download the recorded data to assess the risk of injury and
determine what treatment is required.
1.1 Objective
The objective of the TB-Eye design is to create a small and lightweight device that attaches to a
pair of glasses to detect possible traumatic brain injury in people participating in sports. The device will
be usable for several different sports, unlike helmets which are designed specifically for one sport. In
contact sports such as football, head impacts are common and expected, but in non-contact sports like
cycling or skiing head impacts are less frequent and more likely to go unnoticed or untreated especially if
a person is alone or far from medical facilities. Football helmets with integrated sensors already exist on
the market, like Riddell’s Revolution IQ HITS football helmet [1], but they are bulky, expensive, and
cannot be justified for sports with infrequent head impacts. The goal of the TB-Eye device is to record
significant impacts to the user’s head and to be unobtrusive by keeping size and weight to a minimum
while maintaining a reasonable cost and recording significant impacts to the user’s head.
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1.2 Motivation
In the United States, approximately 1.5 million people suffer from TBI each year. Of those,
50,000 die as result of their injuries and 85,000 have long term disabilities. Currently there are 5.3
million people living with these disabilities. Among the causes of TBI are deceleration injuries caused by
the head impacting a stationary object. During rapid deceleration events, the brain moves at a different
speed than the skull and different parts of the brain itself experience differential speed. These differences
in movement rate result in brain swelling, contusion, and individual neurons’ axons being broken; these
are causes of TBI [2].
Mild TBI is the “result of the forceful motion of the head or impact causing a brief change in
mental status (confusion, disorientation or loss of memory) or loss of consciousness for less than 30
minutes” and is often missed at the time of injury because symptoms are not always outwardly visible,
and the victim may be too confused or disoriented to recognize the symptoms [3]. For moderate to severe
injuries, it is particularly important to get treatment in the first hour after an injury to prevent additional
damage to the brain and worsening of the patient’s condition that may lead to death [4]. The TB-Eye
system will allow users to be alerted of injury so that they may seek medical attention immediately.
No inexpensive, lightweight, and adaptable TBI monitoring systems are currently on the market.
Systems currently available, such as Riddell’s Revolution IQ HITS football helmet, are expensive and are
designed specifically for one sport [1]. The TB-Eye system is a new product that will find application in a
wide range of athletic activities and sports without hindering the user’s athletic performance.
2.
Project Description and Goals
The TB-Eye TBI monitoring system will monitor the acceleration experienced by the user and
determine if a significant risk of brain injury exists. The system will consist of an accelerometer to
measure impact, a microcontroller to determine if risk of TBI exists, and a wireless transmitter to report
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the data to a PC. The PC will display the received data graphically and clearly indicate whether the user is
at significant risk of TBI. The device will run on a 3.7 volt battery and will attach to the frame of a pair of
sunglasses. The device is integrated on two separate boards to allow it to be mounted on each side of the
glasses so that the weight may be evenly distributed.
The TB-Eye glasses will have the following features:







Three axis accelerometer to measure impact
Store impact data in the microcontroller’s memory
LED light located in the peripheral field of vision to notify user of impact requiring medical
attention
o Switch located near light to turn light off.
Wireless transmitter to send data to a computer
A rechargeable lithium polymer battery usable for a minimum of one day of operation
o Battery will be located on opposite side of eyewear from device to provide even weight
distribution
A graphical interface to display and analyze data
Minimal form factor proportional to eyewear’s frame, mounted to side of frame.
Unfortunately, an accelerometer with the range necessary for full TBI detection was unavailable. This
limits the ability of the device to determine the severity of an injury, however it will still detect any
impact that it can withstand. The device can be easily modified to include full detection range by
incorporating the proper accelerometers. Additionally, due to difficulties with the implemented
microcontroller, the prototype PCB did not achieve full operation, but a fully functional prototype was
built and demonstrated on a breadboard.
3.
Technical Specifications
The technical specifications for the TB-Eye system are shown in Table 1. The power
consumption, supply voltage, and battery capacity requirements ensure that the device will operate
normally for at least one day without recharging. The power consumption of the device is significantly
lower than the target consumption; this allowed the battery capacity to be reduced without compromising
the operational life of the device. The accelerometer with the target range specified below will measure
any impact an athlete is likely to encounter without any significant loss in sensitivity. The achieved
accelerometer range will not allow analysis of impact severity for anything beyond minor impacts. The
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dimensional properties of the device were modified during design to meet the qualitative requirements of
a lightweight and unobtrusive device. As a result, two separate PCB boards were made so that the size of
each board would meet the target specification.
Table 1. Technical Specifications for the TB-Eye System
Specification
Target
Actual
Power Consumption
Supply Voltage
Battery Life
Battery Capacity
Weight
Size
61.67 mW
3.7 V
1 day of normal operation
400 mAh
50 g
Less than 10.2(4) x 1.5(0.6) x
0.51(0.2) cm(inches) L x W x H
Acceleration Range
Acceleration Recording Threshold
Acceleration Alert Threshold
Accelerometer Sampling Rate
(Idle)
Accelerometer Sampling Rate
(Active)
Wireless Transmission Protocol
Transmission Power
Transmission Range
Data Storage
±100g in all three axes
10g
50g
2 kHz
13.2 mW
3.7 V
1 day of normal operation
110 mAh
14.5g/ 46.2g with glasses
8.64(3.4) x 1.78(0.7) x
0.9(0.35)
(3.68)1.45 x 1.27(0.5) x
0.56(0.22)
±16g in all three axes
10g
10g
3.2kHz
6 kHz
3.2kHz
ANT+
0 dBm
10m
Stores the value of acceleration
and time elapsed since the impact
occurred.
Displays the acceleration data
graphically
Bluetooth
2 dBm
10m
Stores the value of
acceleration
GUI
4.
Design Approach and Details
4.1
Design Approach
Displays the acceleration data
graphically
Overview
The TBI monitoring system features a three-axis accelerometer, a microcontroller, an EEPROM
memory module, a wireless transmitter, a wireless receiver, a PC, an LED, and a 3.7 V battery. The block
diagram, shown in Figure 1, shows how the components are connected. The accelerometer,
microcontroller, memory module, and transmitter are integrated onto a PCB, which is mounted on the
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frame of a pair of sunglasses. A second PCB contains the battery and other power electronics which is
mounted on the opposite side of the sunglass from main PCB. The accelerometer monitors acceleration
data for all three axes of motion and uses internal thresholding to trigger an interrupt pin when
acceleration exceeds the threshold defined in code. The microcontroller then reads the data from the
accelerometer and passes the data to the EEPROM memory module. The microcontroller also activates a
warning LED on the board if the minimum acceleration threshold is reached.
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Figure 1. High-level block diagram for the TB-Eye TBI Monitoring System.
The main PCB, battery, and power board are mounted on the frame of the sunglasses as shown in
Figure 2. The main PCB includes the accelerometer, the bluetooth transmitter, the EEPROM, the
notification LED, and additional passive. The LED is at the end of the board so that it is visible to the
wearer without impairing his or her vision.
Notification LED
Accelerometer
Power Board
Battery
Figure 2. Device mounted on a pair of sunglasses.
Impact Sensing
The device includes an Analog Devices ADXL345 accelerometer. The accelerometer has a ±16g
measurement range in all three directions, and it has a maximum sampling rate of 3.2KHz. Because TBI
events are short, the sampling rate is normally set for the 3.2KHz maximum. The accelerometer
communicates with the microcontroller over a 4 wire SPI connection with wires for MISO, MOSI, Clock,
and Chip Select. There are two additional wires for the hardware interrupt pins, INT1 and INT2, which
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are used to tell the microcontroller when the threshold is exceeded, and when the next data value from the
accelerometer is ready. Having the microcontroller wait for interrupts allows it to be put in sleep mode to
save power, though this feature was not implemented in time for the demo. If the acceleration value is at
least 10g, the microcontroller turns on the LED on the board indicating that the user must seek medical
attention. Upon detection of an above-threshold acceleration, the microcontroller begins to write the
incoming accelerometer data to an array with a length of 300 bytes (50 data points). When the array is
full, the microcontroller ceases to read from the accelerometer and writes the array to the EEPROM
memory chip on the device. When the GUI requests data, the microcontroller reads it in from the
EEPROM and sends it over Bluetooth to the PC.
Wireless Transmission
The wireless transceiver is a Roving Networks RN-42 Bluetooth module, which draws a sleep
mode current of 28uA. When the transceiver receives a signal from the GUI, it relays that to the
microcontroller. The Bluetooth transceiver is connected to the microcontroller by a UART serial
interface. When the signal from the GUI is received, the microcontroller reads the acceleration data from
the EEPROM chip and transmits it through the Bluetooth serial connection.The data can be received by
any device that supports the Bluetooth Serial Port Profile (SPP), which includes most built-in and USB
Bluetooth devices. The data could also be sent to a smartphone or handheld device, however the team did
not have the time or resources to implement this feature.
Graphical User Interface (GUI)
A GUI, shown in Figure 3, implemented in MATLAB runs on a PC connected to the wireless
receiver. A python script is used to handle serial communication with the device because the MATLAB
serial libraries are not well supported on Mac OS X. The script is called by pressing the “Read Data
From Device” button in the GUI. The Python script requests data from the device and formats the raw
data into meaningful acceleration values. The formatting is done by combining each pair of values into
one 16-bit value, normalizing this value according to the resolution of the accelerometer, finding the
magnitude of each triplet of data points, and converting the result into an array of floating point numbers.
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The script then saves the array in a text file to be loaded into MATLAB. The GUI displays the data
graphically, with the acceleration threshold clearly shown. The critical threshold is shown as a red line on
the graph, emphasizing any data over that threshold. Data is displayed both in graphical and tabular form.
Figure 3. GUI displaying force (g) detected by the accelerometer over time (s). Next to the graph is a
table that numerically displays the data.
4.2
Codes and Standards
1. Bluetooth v2.0 is a proprietary wireless networking protocol and embedded system designed for
wireless sensor networks. It features



Flexible PANs
Class 2 power output of 2.5mW
Class 2 range of approximately 10m
2. Universal Serial Bus (USB) is used to recharge the battery. It may also be used to connect a
Bluetooth receiver to a PC if the PC does not have an imbedded receiver. USB features
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


Plug-and-play capability
5V power requirement
480 Mbps data transmission rate [21]
3. Synchronous Serial Interface (SSI) is used by the ATMega368 microcontroller for connection to
the wireless transceiver. It features


Supports Microwire, Synchronous Serial Protocol (SSP), and Serial Peripheral Interface
(SPI) protocols
7.2kHz-24 MHz transmission bit rates [22]
4. (I2C) is used by the ATMega368 microcontroller for connection to the EEPROM memory
module. It features



5.
Attachment of low-speed peripherals to main controller
100kbit/s standard mode speed
Two bi-directional lines for data and clock
Schedule and Tasks
The Gantt chart for the development of the TB-Eye system is shown in Appendix A. All tasks
shown were be performed by all members of the team. The first critical task in the development process
was the schematic design. As shown in the chart, the schematic design was a predecessor for the PCB
layout and assembly of the device. Because of delays in designing the PCB, assembly and testing was
pushed back until the end of November. Complete testing could not be performed on the device.
6.
Results and Acceptance Testing
Full testing could not be performed because the PCB prototype could not be programmed as
expected. As a result, limited testing was performed on the breadboard prototype. To test the prototype
current consumption, the device was powered by a bench power supply connected through a digital
multimeter in DC current mode. The current was measured when the device was in various modes of
operation. Of particular importance is the current in idle mode where the accelerometer is sampling and
checking for samples above the threshold, but the rest of the device is inactive. This is the mode that the
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device spends the most time in, and as a result battery life should be determined in this mode. The
average current in idle mode was measured to be approximately 4mA, which will result in a battery life of
26 hours using the 110mAh battery. The accelerometer is calibrated by aligning each axis to vertical and
calibrating the value to 1G, then aligning each axis to horizontal and calibrating the value to 0G.
Alignment with respect to the earth’s gravity will be checked with a bubble level. This procedure results
in calibration values for the particular accelerometer used, which can be programmed into the code. To
test for accelerometer accuracy, the device will be mounted on a simulated head such as a crash test
dummy head, which will be impacted with forces expected to be similar to impacts that may cause TBI.
The data recorded by the device will be compared to data recorded by a calibrated accelerometer to verify
that the magnitude calibration and timing are correct. The project demonstration was successfully
preformed on December 14. The threshold was set to a low value, 2G, and the device was triggered by
tapping the board. It was shown that this triggered the notification LED. The data was then loaded into
the GUI for display and analysis.
7.
Budget and Cost Analysis
Table 2 shows the cost to build one PCB prototype, the total cost of which is $78.94 The total
cost for all parts and equipment for the project was $234. Not included in these costs is the price of the
Oakley M frame glasses for $129 MSRP, which were loaned to us from GTRI.
Table 2. Cost for one PCB
Quantity
Unit Price
PCB
1
$33
Accelerometer
1
$7.79
Microcontroller
1
$4.87
Battery
1
$6.95
USB Charger
1
$0.85
EEPROM
1
$4.82
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Wireless Transceiver
1
$15.95
Micro USB Port
1
$1.10
Misc parts (resistors,
capacitors, LEDs)
Total
$3.61
$78.94
Table 3. Breakdown of Spending
Development parts
$69.85
Parts for PCB Prototype
$78.94
Unused parts (spare parts, or parts for an older design iteration)
$85.21
Total
8.
$234.00
Conclusion and Future Work
A working breadboard prototype has been demonstrated, and the PCB prototype is complete aside
from issues getting the program to run on it. One important change to be done in the future is switching o
a full 100G range accelerometer. Since all 100G accelerometers on the market are analog, using one will
require more work to be done on the microcontroller, including analog to digital conversion and threshold
detection. For the PCB prototype, additional size reductions are possible by making changes such as using
a multi-layer board, using smaller components, using a thinner board, and eliminating some of the headers
required for prototyping, and using smaller headers when they are required. It may also be possible to
make a custom integrated circuit that combines several of the key parts, however this would be very
costly. Another feature not addressed by this project is integration with the glasses frame. Similar to the
Oakley MP3 sunglasses, the device could be built into the frame if it could be made small enough. It may
also be useful to find a way to more securely attach the device to the user’s head, whether that is more
secure glasses or a different attachment method such as a headband. Finally, additional value could be
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added if a smartphone application was developed, but the decision to use Bluetooth was made late in the
design process and the team did not have the resources to develop a mobile applications.
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References
[1]
Riddell. “Riddell Revolution® IQ HITS™ Helmet”. 2011. [Online]. Available:
https://shop.riddell.com/riddell/app/displayApp/%28cpgsize=20&layout=7.07_2_3_75_12_13_67_78_6_4_5_6&uiarea=6&carea=0000000001&cpgnum=1&citem=000000
00010000000009%29/.do?rf=y. [Accessed: September 21, 2011].
[2]
Traumatic Brain Injury.com, LLC. “What are the Causes of TBI?”. 2004. [Online]. Available:
http://www.traumaticbraininjury.com/content/understandingtbi/causesoftbi.html
[Accessed: September 21, 2011].
[3]
Traumatic Brain Injury.com, LLC. “Mild TBI Symptoms”. 2004. [Online]. Available:
http://www.traumaticbraininjury.com/content/symptoms/mildtbisymptoms.html
[Accessed: September 21, 2011].
[4]
Kluger, Jeffrey. "Dealing with Brain Injuries,” Time Magazine, 6 April, 2009. [Online],
http://www.time.com/time/magazine/article/0,9171,1887856,00.html. [Accessed: 25 September,
2011].
Bibliography
[5]
E. Blackman. Helmet Protection against Traumatic Brain Injury: A Physics Perspective.
[Online]. http://www.pppl.gov/colloquia_pres/WC25MAR09_EBlackman.pdf [Accessed 25 Sept.
2011].
[6]
J. Gever, “Any Football Helmet Hit Can Cause Potential Concussion,” MedPage Today, 7 Dec.,
2007. [Online]. http://www.medpagetoday.com/Neurology/GeneralNeurology/7625 [Accessed 25
Sept. 2011].
[7]
Analog Devices. “The Five Motion Senses: Using MEMS Inertial Sensing To Transform
Applications”, 2009. [Online]. Available: http://www.analog.com/en/mems-sensors/high-gaccelerometers/products/whitepapers/over_Five_Motion_Senses/resources/fca.html [Accessed 5
Sept. 2011].
[8]
Measurement Specialties, “Vibration Sensor - Model 832 Accelerometer,” September 2011.
[Online]. Available: http://www.meas-spec.com/product/t_product.aspx?id=5593 [Accessed 4
Sept. 2011].
[9]
Piezocryst, “Basics: Piezoelectric Sensors,” September, 2011. [Online]. Available:
http://www.piezocryst.com/piezoelectric_sensors.php [Accessed 5 Sept. 2011].
[10]
Measurement Specialties, "Model 832 Accelerometer," Model 832 Accelerometer datasheet, July
13, 2011
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[11]
Microchip Technology, “nanoWatt XLP eXtreme Low Power PIC®MCUs,” Apr. 2010 [Online].
Available: http://ww1.microchip.com/downloads/en/DeviceDoc/39941d.pdf [Accessed 5 Sept.
2011].
[12]
Texas Instruments, “Choosing An Ultralow-Power MCU,” Application Report SLAA207, Jun.
2004.
[13]
Texas Instruments, “Low-Power FRAM Microcontrollers and Their Applications,” White Paper
SLAA502, Jun. 2011.
[14]
Nordic Semiconductor. (September 2006). Single chip 2.4 Ghz Transceiver with Embedded ANT
protocol. (Rev. 1) [Data Sheet]. Available:
http://www.nordicsemi.com/eng/nordic/download_resource/6615/1/97271469 [Accessed: 18
Sept. 2011].
[15]
ANT Wireless. “ANT Wireless – Providing Technologies That Lead the Globe”, 2011. [Online].
Available: http://www.thisisant.com/company. [Accessed: 26 Sept, 2011].
[16]
Erstellt, “Description Pan13XX Series,” Panasonic Elect. Dev. Euro. GMBH, Lüneburg, DE,
App. Note AN-13xx-2400-111, Feb. 2011.
[17]
ANT Wireless. (2011). “ANT+ Connecting Sensors for Life!”. [Online]. Available:
http://www.thisisant.com/ant/ant-interoperability [Accessed: 6 Sept. 2011].
[18]
Bluetooth. “Low Energy”, 2011. [Online]. Available: http://www.bluetooth.com/Pages/LowEnergy.aspx. [Accessed: 26 Sept, 2011].
[19]
ANT Wireless. “Technology”, 2011. [Online]. Available: http://www.thisisant.com/technology.
[Accessed: 26 Sept, 2011].
[20]
ANT Message Protocol and Usage. Rev 2.9. Dynastream Innovations Inc. Alberta, CA. 2 Jul.,
2007. pp.7-15.
[21]
Universal Serial Bus Specification. Rev 2.0. Compaq et. al. Palo Alto, CA, USA. 27 Apr. 2000.
pp. 1-175.
[22]
Jz4740 Peripheral Specification. Rev 1.0. Ingenic Semiconductor Co., Ltd. Beijing, PRC. 2007.
pp. 1.
[23]
P. McCaffrey, Ph.D. (2008). Chapter 11. Traumatic Brain Injury: Effects of Closed Head
Injury. The Neuroscience on the Web Series: CMSD 636 Neuropathologies of Language and
Cognition. [Online].
http://www.csuchico.edu/~pmccaffrey/syllabi/SPPA336/336unit11.html [Accessed: 25
Sept. 2011].
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Appendix A. Gantt Chart.
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