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FALL DETECTION WITH THE BT-BOX
Ben Valdovinos
Sonoma State University
Engineering Science
Introduction• Physical activity• Methods to measure physical activity• Accelerometers• My work with Accelerometers and PIC• Progress • Limitations• Future work
Why Measure Physical Activity (PA)?• PA links human movements to health status• Studied in the areas of cardiovascular diseases• Falling is one of the most significant causes of injury for
elderly citizens
MainlyFalling is one of the reasons why many otherwise healthy individuals are forced to leave the comfort and privacy of their own home to live in an assisted-care environment.
• Physical activity• Methods to measure physical activity• Accelerometers• My work with Accelerometers and PIC• Progress • Limitations• Future work
Current Methods for Measuring PA• Pedometers• Actometers• Gyroscopes• Video recording
• Physical activity• Methods to measure physical activity• Accelerometers• My work with Accelerometers and PIC• Progress • Limitations• Future work
The Best Method: Accelerometers• Measuring PA using accelerometry is preferred• Acceleration is directly proportional to external force• This reflects the intensity and frequency of human
movement• Some accelerometers even provide tilt sensing data
• This allows the classification of posture
Brief History of Accelerometers• Earliest development is credited to Burton McCollum and
Orville S. Peters [7]• Weight: 1lb• Size: ¾” x 1-7/8” 8-1/2” • $420 in 1923• Implemented in bridges, dynamometers, and aircrafts
Common Types of Accelerometers• Capacitive Change in capacitance related to acceleration
• Piezoelectric Piezoelectric crystal– voltage output converted to acceleration
• Piezoresistive Resistance changes with acceleration
• Hall Effect Motion converted to electrical signal by sensing of changing magnetic fields
• Magnetoresistive Material resistivity changes in presence of magnetic field
• Heat Transfer Location of heated mass tracked during acceleration by sensing temperature
Acceleration in Human Terms• What are some “g” reference points?
Description “g” level
Earth’s gravity 1g
Passenger car in corner 2g
Bumps in road 2g
Indy car driver in corner 3g
Bobsled ride in corner 5g
Human unconsciousness 7g
• Physical activity• Methods to measure physical activity• Accelerometers• My work with Accelerometers and PIC• Progress • Limitations• Future work
Create Something
Process
Goals
Idea
Lit ReviewConstraints
Evaluation
Goals• Harness accelerometer technology• Detect a human fall• Making device practical • Incorporation into everyday rehabilitation practice• Provide user with the feeling of safety• Complete my Capstone Project course
Goals
Idea
Lit ReviewConstraints
Evaluation
Goals
Idea
Lit Review
Constraints
Evaluation
The Answer• Perfect resolution to this problem:• incorporate fall detection in to smart phones• They are small, robust, decent battery life• People already carry them
Embedded Inside
Goals
Idea
Lit ReviewConstraints
Evaluation
Adjustment• Make it an acceptable Senior Project
Embedded Inside
Goals
Idea
Lit ReviewConstraints
Evaluation
What is it?• The BT-Box is a general purpose Bluetooth based data
acquisition system • BT-Box’s technology is general purpose and its
applications are very diverse• Applications in the medical field
• Fall Detection
• Applications in the environmental field• Temperature and humidity sensing
What does it do?• Connects computers or smart phone to sensors• Bluetooth communication • Data storage on micro SD card• Accepts different sensors • Reprogrammable• System runs on a re-chargeable battery• Implement Fall-Detection Algorithm
SENSORS
BT-Box
SD Card
Bluetooth
MCU
Various Sensor Input
Micro USB
System Level Block Diagram
Fall Detected!!
Fall Detection Application
Information
Intervention
Current Project State• Accuracy of clock waveforms• Accessing all IO Pins• Developing I2C
Fall Detection• Start of the Fall
• Vector sum of 3-axes will tend towards zero
• Substantially less than 1-g • FREE-FALL interrupt
• Impact• Shock detected by ACTIVITY interrupt
• Aftermath• Human body doesn’t rise immediately
after fall• INACTIVITY interrupt
• Compare before and after
Fall Detection
Accelerometer
Accelerometer fall detection• 8 interrupts
DATA_READY, SINGLE_TAP, DOUBLE_TAP, ACTIVITY, INACTIVITY, FREE_FALL, WATERMARK, and OVERRUN
• Algorithm• Determine the start of the fall• Detect impact, which has
largest impact• Aftermath: body doesn’t rise
immediately• Comparing orientation
before and after.
Other Applications
Small Weather Station
• Connect other sensors:• Temperature• Humidity• Etc.
• Save data on SD Card
Use Your Imagination
• Hardware is provided:• SD Card for data storage• IO Ports for control• Bluetooth capability
Cost
Hardware Software
Item Price
32-bit PIC $5.00
Bluetooth Module $15.00
Accelerometer $13.00
SD Card $4.00
Various Parts $25.00
Total $62.00
Item Price
MPLABX Free
Eagle Free
Python Free
Timeline
Team of 3 Team of 2 Solo0
1
2
3
4
5
6
Time To Market
Months
Software on PC• Python programming language
• Allows communication to the BT-Box• Freely usable and distributable, even for commercial use
• Eagle • Free• PCB Design
Related EE Courses• Microcontrollers – ES 310• Electronics – ES 330/230• Wireless Communications – ES 485-03• Analog and Digital Communications – ES 442• Electromagnetic Theory – ES 430• Any course that requires deep problem solving
References• [1] J. A. Stevens, P. S. Corso, E. A. Finkelstein, and T. R. Miller, "The costs of
fatal and non-fatal falls among older adults," Inj Prev, vol. 12, pp. 290- 5, 2006.
• [2] Microchip website: http://www.microchip.com • [3] Dr. Farahmand’s website: http://www.sonoma.edu/users/f/farahman/ • [4] SD Group Technical Committee, SD Card Specifications: Physical Layer,
Version 3.01• [5] Detecting Human Falls with a 3-Axis Digital Accelerometer, Ning Jia,
Analog Dialogue 43-07, July (2009) 7• [6] http://www.sonoma.edu/users/f/farahman/sonoma/courses/capstoneproject_1/syllabusweb.htm
• [7] Walter, Patrick L. The History of the Accelerometer: 1920 – 1996. Ft. Worth, Texas. 2006
Questions?• www.benvaldo.com