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