The document describes a sports attachment monitoring module (SAMM) that detects impact force to an athlete's head. The SAMM uses an accelerometer attached to a helmet to measure g-forces, an XBee to transmit data wirelessly, and a Raspberry Pi to receive data and alert medical staff if thresholds are exceeded. The SAMM aims to monitor concussions and improve safety for athletes in contact sports.

1. Sport Attachment Monitoring Module (S.A.M.M.)
EE198B
San Jose State University, Department of Electrical Engineering
Fall 2016
Faissal Antar, Wireless ​Communication Systems
faisdnice@hotmail.com
Daniel Beebe, ​Circuit Design
danielbb3​ @yahoo.com
Jesus Flores, ​Software Programming
jesusf510@gmail.com
Kevin Pineda​,​ App Developer
simplykevv@gmail.com
Dr. Robert Morelos-Zaragoza,​ ​Advisor
Robert.morelos-zaragoza@sjsu.edu

2. Table of Contents
Abstract 2
Introduction 3
Project Importance 6
Theory 7
Overview 7
Flowchart 7
ADXL337 Accelerometer 8
Xbee Pro 60mW Wire Antenna Series 1 9
Xbee Explorer Regulated 10
Xbee Explorer USB Dongle 11
RJD3555 Series Coin Cell Rechargeable Battery 12
Adafruit Micro Lipo USB Li-Ion Charge Controller 13
Raspberry Pi 3 15
Python Script (Software) 16
Specifications 18
Manufacturing Costs & Labor 19
Results 20
Future Developments 23
Conclusion 24
References 25
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3. Abstract
This project involves the design of a sports attachment monitoring module that
can be attached to any sporting helmet in order to detect intensity of impact force
experienced to the head. The aim of this project is to monitor concussions that are rapidly
becoming epidemic in contact sports. Once the assigned safety threshold value is
exceeded, medical staffs and coaches on the sideline will be alerted in order to
immediately remove the players from the field to undergo the concussion protocol that
would ensure their safety and thereby prevent further potential injuries. The object of
the S.A.M.M. (Sports Attachment Monitoring Module) will be to provide an extra
resource for monitoring player safety and well being regarding concussions
Introduction
Traumatic brain injuries have become an epidemic among athletes in the United
States. According to the ​Journal of Athletic Training [5] “​An estimated 300 000
sport-related traumatic brain injuries, predominantly concussions, occur annually in the
United States (US)​. In fact, for young people ages 15 to 24 years, sports are second only
to motor vehicle crashes as the leading cause of traumatic brain injury”. Traumatic brain
injury can be incredibly difficult to detect due to no physical indicating signs. This can
lead to sever long and short term brain injuries including dementia, memory loss, and
brain malfunction. Figure 1 below, shows the concussion rate among US high school and
collegiate athletes by a study done by, ​National Collegiate Athletic Association Injury
Surveillance System [6].
3

4. Figure 1​. ​Concussion rate among US high school and collegiate athletes.
Sports have become more popular in high school and collegiate level, and the
number of traumatic brain injuries have been increasing. Concussions represented 8.9%
(n = 396) of all high school athletic injuries and 5.8% (n = 482) of all collegiate athletic
injuries​[5]​. Whether the sport is contract or not, there are still a lot of traumatic brain
injuries in all sports, which includes both sexes. Figure 2 below, shows percentage of
traumatic head injury in all sports, including both sexes. Although there are rules in
place to help maximize the safety of the players; physical and mental damages cannot be
prevented but can be monitored and recorded for better treatment options.
4

5. Figure 2​. Percentage of total Head Injuries.
Depending on the particular individual, the recovery time can fluctuate causing
potential harm to the individual if they are not monitored correctly. The elusiveness of
the concussion makes it extremely difficult for medical staff to detect, therefore delaying
mandatory medical attention. Having the proper training equipment and training staff is
essential in the safety of the individuals. By monitoring athletes head trauma in high
school and collegiate level, there is a better chance to improve the quality of treatment on
an individual and reduce traumatic brain injuries. Figure 3 below, illustrates the
returnable time table for an individual after a concussion has occurred.​[5]
5

6. Figure 3.​ Length of Returnable time table for Individual Athlete.
Project Importance
The S.A.M.M. project aims to address the issue of concussions in sports by
creating an electronic module that can be attached on any sporting helmet in order to
monitor the intensity of impact force that is being applied to the athlete’s head. By
keeping track of the collision forces applied to the head, sideline staff can be easily
alerted when an athlete has been hit hard enough to warrant a concussion protocol check
up. The overall goal of this project would be to Monitor health condition of athletes, raise
awareness of concussions, contribute towards concussion mitigation, and provide a future
for young athletes that are involved in contact sports.
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7. Theory
Overview
SAMM consists of two key elements: a transmitter and a receiver. With these two
elements, changes in forces acted upon a player’s head can be monitored. The transmitter
component will be attached to the helmet. The transmitter consists of 3 components that
include a 3-axis accelerometer, transmitting Xbee (radio module), and rechargeable
battery. The accelerometer produces analog voltage based on the change in gravitational
force it experiences in either the X, Y, or Z direction. These output voltages are
connected to the transmitting Xbee where the analog voltage signal is converted to a
digital signal through the onboard 10-bit ADC on the Xbee. This digital signal is then
sent from the transmitting Xbee to the receiving Xbee.
The receiver unit of the S.A.M.M. consists of the Raspberry Pi 3 microcontroller
coupled with another Xbee module that is configured to be a receiver. The Xbee is
connected to the Raspberry Pi through a Universal Asynchronous Receiver/Transmitter
(UART) connection. UART is a universal method for receiving and transmitting data
between two peripherals. In this case the Xbee will be sending the data to the Raspberry
Pi, where the data will be decoded and interpreted into useful information.
Flowchart
The arrangement of the components of the S.A.M.M can be seen in the flowchart
provided below.
7

8. Figure 4.​ Flowchart showing connection of the components of the S.A.M.M.
Figure 4 ​shows the flowchart with green blocks representing inputs, blue blocks
representing Radio Frequency (RF) modules, and a yellow block representing the main
computing power for the module. As shown in ​Figure 4​, the accelerometer will send
analog voltage data to the transmitting Xbee. Then the data is transmitted between Xbees
through RF communication. Once the data is transmitted between the Xbees, it is send to
the Raspberry Pi through UART. After the Pi receives the data, it is processed, stored,
and displayed on an LCD display connected to the Pi.
ADXL337 Accelerometer
The ADXL377 is a small, thin, and low power, 3-axis accelerometer with signal
conditioned voltage outputs. The main function of ADXL377 accelerometer is to measure
dynamic acceleration produced by movement, shock, or tremor in the form of
gravitational force (g-force). This sensor has a typical full-scale range of ±200g, which
means that the maximum gravitational force it can detect is +200g and a minimum of
8

9. -200g. A single gravitational force of acceleration (1g) is equal to the Earth’s
gravitational force on an object, which is 9.81 ​m/s​2​
. ​The outputs of each accelerometer
axis are output in an analog signal.
Figure 5. ​ADXL337 accelerometer
This accelerometer was chosen for the S.A.M.M. design because it had a range of
200 g's. Research shows that concussions are most likely to be induced after an athlete
experiences over 100 g's of force to the head. In order for the module to monitor
concussions properly, it is important for the accelerometer be capable of handling at least
100g. The ADXL337’s range is large enough to detect a possible concussion, which
fulfills requirements of the objective.
Xbee Pro 60mW Wire Antenna Series 1
The Xbee Pro is a radio frequency module that facilitates reliable wireless
communication between. This RF module is a low cost and power wireless sensor
network that was designed to meet the IEEE 802.15.4 technical standard.
9

10. The project design incorporates the use of two Xbee pro modules with one
configured as a transmitter and the other as a receiver. The Xbee Pro modules were
chosen as transceivers due to low power consumption, high configurability, and long
range data integrity that can cover a distance of a mile which is much greater than the
size of most sport fields. Each module contains a 10-bit ADC converter that welcomes
both analog and digital inputs from various components, therefore is compatible with all
components used in the S.A.M.M.
Figure 6. ​Xbee Pro Module
Xbee Explorer Regulated
The Xbee Explorer regulated is a unique power regulator that is compatible with
all the different types of Xbee modules. The Explorer converts the 5V signals to 3.3V so
that a 3.3V-5V system can be used to any Xbee module. It also contains Xbee sockets
which enables the attachment of any Xbee module onto it. The attachment of an XBee
onto this breakout board will provide direct access to the serial and programming pins on
10

11. the XBee unit. Furthermore, it also contains four LED indicator that shows whether or
not the transmitting and receiving Xbee units are communication with each other or with
the accelerometer.
The Xbee Explorer Board was primarily used to for debugging and design testing
of the SAMM. Although useful, The Explorer Board is not necessary for a Xbee to
transmit or receive data. Due to the limited space inside of many sporting helmets, the
Xbee Explorer Board will not be attached to the transmitting Xbee. The receiving Xbee
will utilize the Explorer Board.
Figure 7. ​Xbee Explorer Regulated
Xbee Explorer USB Dongle
The Xbee Explorer USB Dongle is a module that enables interface with the Xbee
unit. It serves as a gateway between the Xbee unit and the X-CTU software that is used to
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12. configure Xbee modules, test wireless connection, and relay data between a computer and
remote Xbees. This module played a very crucial role in configuring one Xbee as a
transmitter and the other as a receiver by providing a gateway to the X-CTU software that
could configure the input pin of an Xbee as either analog or digital.
Figure 8. ​Xbee Explorer USB Dongle
RJD3555 Series Coin Cell Rechargeable Battery
The battery chosen for the S.A.M.M. was the RJD3555 Series Coin Cell
Rechargeable Battery. This battery was chosen due to its compact size and power
capabilities. The total transmitting circuit required at least ​251 mAh and ​3.6V. A battery
with ​250mAh would allow the S.A.M.M. to operate for about one hour, if it was operating
at max power for the entire time. For a generous buffer of battery life between charges,
this ​3.7V 500mAh RJD3555 battery was chosen. Assuming the transmitting circuit
operates at max power for two whole hours, which is highly unlikely, the S.A.M.M. will
be able to function for two hours. This operation time is well within the playing time of
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13. most sports that will utilize the S.A.M.M. A player wearing a S.A.M.M. will
comfortably know that the battery charge will be enough for at least one playing session
in between charges.
Figure 9. ​RJD3555 Series Coin Cell Rechargeable Battery
Adafruit Micro Lipo USB Li-Ion Charge Controller
Figure 10. ​Micro Charge Controller
13

14. To charge to RJD3555 battery cell, a separate charge controller will accompany
the S.A.M.M.. The charging unit that is used is the Adafruit Micro Lipo USB Li-Ion
Charge Controller. This charge controller was selected based on its quick charging
capabilities and compatibility with the type of battery that is used for the S.A.M.M. This
charge controller also is versatile because of its required micro-USB input, which is
common with many other charging devices.
LCD Screen
The purpose of the LCD screen is to display the results being read from the
SAMM to the user. In order to pair the LCD screen to the raspberry pi; the driver for the
LCD screen provided by the manufacturer has to in installed into the raspberry pi. Also,
the config.txt file for the Pi must be configured in order for the screen to be displaying
properly. The config.txt file is read at each boot by the ARM processor on the Pi to
configure the settings at each boot. Both the driver setup and boot text file configuration
is essential for proper use of the LCD screen​.
14

15. Figure 11. ​Raspberry Pi LCD screen
Raspberry Pi 3
The Raspberry Pi 3 is a small, affordable credit card sized computer that can be
used in several applications. It has a lot of peripheral support, which is perfect for this
application.
Figure 12. ​Raspberry Pi 3 Model B
15

16. For the purposes of the module, the peripherals needed include the the GPIO
pins, HDMI port, and a few of the USB ports on the Raspberry Pi. The Pi comes
equipped with all of these which makes it the perfect computer to handle the processing
needs, the Raspberry Pi was chosen due to its expandable storage capabilities. The Pi is
run off an Operating System which needs to be installed onto a micro-SD card before
being able to power on and function. Since the module is designed to store the data
received, it needs to have a capability of having a large storage space. With micro-SD
card technology advancing to the point where it can store almost terabytes of data, a
micro-SD card is more than capable than handling the storage needs of the module. In
order to interpret the data being received by the Xbee, a python script was written to the
Pi which will continuously run and display the results for the user.
Python Script (Software)
In order to process and interpret the data being received by the Xbee, a program
needs to be implemented to handle all the data. Python was chosen as the language the
program will be written in for its simplicity and power. In order to properly run the code,
some important libraries need to be installed first. The libraries installed include the Xbee
libraries, and the Serial Port libraries. The first step in python program is to open the
Serial Port in which the data is received, which is the UART pin on the Raspberry Pi’s
onboard GPIO pins. Once the connection is open, the script file can now take in data
from the Xbee.
16

17. The first step in processing the data is to set up a zeroed value for all future
readings. The program begins with an initialization at each boot. It samples the first 50
readings from the accelerometer and calculates an average value for all three axes. This
value is store and then subtracted to every new value read in order to zero out the
readings. Since the orientation of the accelerometer affects the base readings, it is
necessary to zero out the readings in order to get an accurate reading.
Once the zeroed out value is determined, the data is collected from the Xbee
through a UART connection. The data for each axis then needs to be separated, as it
comes in from the Xbee as one long string of data. The separated values obtained are hex
ADC values. In order to understand the data, a conversion equation was designed and
implemented into the program to convert the ADC value into a meaningful force reading.
The reading can easily be turned into a voltage reading by using a reference voltage sent
to the Xbee. The reference voltage was set to 3.3 V, which is supplied through the output
voltage on the ADXL337. The sensitivity is used in order to determine how much voltage
is produced for each g of force applied. For the ADXL337, the voltage sensitivity is 65
mV/g. The following equations are used in order to complete the conversion:
( )V OUT = 1023
ADC Reading
* V REF
Equation 1.​ Voltage conversion equation (in V) for a 10-bit ADC
( )FOUT =
V OUT
65 mV /g
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18. Equation 2. ​Force conversion equation (in g) for the ADXL337
Once the data has been properly converted, it is displayed onto the LCD screen.
While the data is being displayed, it is also being stored in a CSV file. This function was
implemented so that the data can be reviewed later if necessary. The data will help show
patterns in where the player gets hit and plays can be altered to better protect the players.
These values can also be represented visually by plotting the force readings over time.
Specifications
The following table shows the specifications of the components used for the
S.A.M.M. These operating conditions need to be constantly satisfied in order to have the
module functioning properly at all times. Since the module is meant to monitor
concussions, it is necessary to maintain steady readings through the entirety of its use.
Table 1. Project Components and their specifications.
Component Function
Power
Dissipation
(mW)
Dimensio
ns (mm)
Weig
ht (g) Operating
Conditions
Accelerometer
3-axis
sensing low power
3 x 3 x
1.45 1.27
1.8V - 3.6V,
300µA, +/- 200 g
Xbee Pro Transceiver 60
24.38x
32.94 4 3.3 V, 215 mA
Raspberry Pi 3 Data storage 12,500
85 x 56 x
17 45 5V, 2.5A
Xbee Explorer
Regulated
Step down
5V to 3.3 V 1-315 35 x 30 1.5 3.3V, 500mA
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19. Manufacturing Costs & Labor
The table below displays the overall costs of the project, with the total cost of the
single sensor model coming out to be $259.93. The SAMM was build while trying to
reduce all costs to a minimum by only purchasing the absolute necessities to ensure that
the prototype was fully functional. The final cost of the project exceeded the estimated
price of 188.97 due to the addition TFT LCD display, the Micro Lipo USB LI-Ion
Charge Controller, and the RDJ 3555 Series Coin Cell Rechargeable Battery.
In regards to labor time, an estimated average time of 28 hours per week was
dedicated to the project itself. A large amount of time was spent on the research during
the summer, and the rest of the time wa spent on building the circuits, configuring the
wireless connection between the xbees, soldering work, and programming the raspberry
pi using python in order to display the results.
Furthermore, in regards to engineering labor costs, the aforementioned
engineering time (28 hours) divided among the four team members comes out to be 7
hours per person. Therefore, a rate of $35/hour for engineering time was used to calculate
that total cost within the last 6 and a half months (26 weeks), thereby yielding a total of
728 hours for project completion. The amount of time dedicated to working on the
project warrants a total $81,500 which is a realistic figure.
Table 2. Overall Cost of project components
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20. Single Sensor Model
Item No. Description Distributor Quantity Price
CM001 Raspberry pi 3 Model B Project Board BlueProton 1 $ 44.44
CM002 Raspberry Pi 3 Case InkBright 1 $ 8.78
CM003 ADXL377 Small, Low Power, 3-axis, +/-
200g
AdaFruit 1 $ 24.95
CM004 XBee Pro 60mW Wire Antenna-Series
1(802.15.4)
SparkFun 2 $ 37.95
CM005 SparkFun XBee Explorer USB SparkFun 1 $ 24.95
CM006 SparkFun XBee Explorer Regulated SparkFun 1 $ 9.95
CM007 RDJ 3555 Series Coin Cell Rechargeable
Battery
Digi-key 1 $ 31.03
CM008 Micro Lipo USB LI-Ion Charge Controller AdaFruit 1 $ 6.95
CM009 Five Inch TFT LCD Display Amazon 1 $ 32.98
Grand Total $ 259.93
Results
Upon reading the individual datasheet for each of the components involved,
components were all implemented together and an early prototype was built. The initial
prototype was implemented on a breadboard in order to test the functionality of the initial
design.
The accelerometer was the first component to be tested due to the fact that the
entire project is dependent upon its analog outputs. This device was therefore tested by
20

21. using a software that contains an inbuilt serial plotter. The X, Y, and Z analog output
component axis of the accelerometer were connected, and a functionality test was
conducted. The result obtained is shown in the figure below. The figure shows a constant
uniform signal for each axis. However, the plotter displayed a big spike every time the
accelerometer was exposed to a sudden movement or a strong hit which indicated a larger
gravitational force (g-force).
Figure 13.​ Serial Plotter Results for analog output component of the accelerometer
Furthermore, as previously mentioned, the module is reduced in size in order to occupy
minimal space within the helmet. As a result, the module will be put on a PCB board, as
shown in the figures below:
21

22. Figure 14. ​PCB board of the Transmitting module with the Xbee
Figure 15. ​PCB board of the Transmitting module with the ADXL377. This is the same
view shown in ​Figure 14 ​with the Xbee not attached.
22

23. The analog output of the accelerometer will be constantly observed on the host
computer in order to keep track of the gravitational forces caused by the intensity of the
collisions. The received data for the X, Y, and Z axis will be displayed on the host
computer, as shown in the figure below. The higher the hit impact, the greater the reading
displayed.
Figure 16​. Readings observed on Raspberry Pi host computer
Future Developments
This prototype has the potential to expand into several different markets. While
the original prototype is meant to target football players, the module can easily be
adjusted to have applications to other sports. This module can be implemented into any
23

24. sport helmet. By simply adjusting the code a little and the casing in which the module is
held it can be retrofitted into the helmet. Big, global potential markets include expanding
the module to be fitted into hockey, baseball, NASCAR, and Formula 1 helmets. By
expanding into other foreign markets, the risk of concussions can be reduced further by
sending players to concussion protocol quicker through the use of the S.AM.M.
Conclusion
The overall objective of this project was to implement better safety precautions
for players in contact sports, as it is nearly impossible to immediately detect whether a
player has received a concussion. Through the use of the S.A.M.M. players will be
monitored through the entirety of the game, with alerts set to go off if any of the set
thresholds are ever surpassed. Early tests show that the designed prototype is functioning
as originally planned. With further tests and research, the S.A.M.M. could lead to a
successful entry into the market.
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25. References
[1] - Digi International Inc., “Xbee/Xbee PRO RF Modules,” Xbee datasheet, 2009.
https://www.sparkfun.com/datasheets/Wireless/Zigbee/XBee-Datasheet.pdf
[2] - Analog Devices, “Small, Low Power, 3-Axis ±200g Accelerometer,” ADXL377
datasheet, 2016.
http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL377. pdf
[3] - Mouser Electronics, “RJD Rechargeable LI-ION Batteries,” iC Illinois Capacitor
datasheet, 2016. http://www.mouser.com/ds/2/88/RJD_series-962351.pdf
[4] - Raspberry Pi • Index page. (n.d.). Retrieved March 02, 2016, from
https://www.raspberrypi.org/forums/
[5] - ​Gessel, L. M., Fields, S. K., Collins, C. L., Dick, R. W., & Comstock, R. D. (2007).
Concussions Among United States High School and Collegiate Athletes. ​Journal of
Athletic Training, ​42(4), 495–503.
[6] - ​NCAA Injury Surveillance System (ISS). National Collegiate Athletic Association.
http://www1.ncaa.org/membership/ed_outreach/health-safety/iss/index.html​.
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