Design and Development of an Accelerometer based Personal Trainer System

By Emer BussmannB.E. Electronic Engineering

April 2008

Introduction

Exercise is the key to a healthy life

Attract interest in running • Allowing user to monitor own

progress• Set achievavle goals

• Satisfaction

Proposal

• Maximum benefit from run• Portability• Low cost

• Track, record and monitor• Achievable goals

Speed Distance

Project Overview

Data Source - Accelerometer• Measures acceleration forces • Capacitance sensor• Triaxial• Minimum cost, portability

and low power consumption • Freescale • X, Y and Z-Axis Channels• Internal Antennae• Status LEDs• Adjustable output frequency• Wireless

SparkFun WiTilt v2.5

Accelerometer Preperation

• Calibration

• Frequency

• Positioning

Bluetooth Suitability

• Wireless• Radio Frequency

• Low power consumption (phone battery)

• Range

Data Acquisistion Unit -LabVIEW suitability-

• Visual programming language • Libraries – functions• Polymorphism • Access of instrumentation hardware

– Serial Communication VI• PDA research

LabVIEW VI Requirements

• Data Importation using serial VI• Data extraction• Save data to file

Serial Communication in LabVIEW

Front panel for the serial communication VI

Data Extraction

Saving Data to a file

 

 

Back end Processing -Matlab Suitability-

• Numerical computing and programming

• Implementation of algorithms • Import Wizard

• Plotting Functions

0 5 10 15

-20

-15

-10

-5

0

5

10

15

20

X-Axis Acceleration

Seconds

Metres/S

econd

2

0 5 10 15

-2

-1

0

1

2

3

4

5

Z-Axis Acceleration

SecondsM

etres/S

econd

2

0 5 10 15-3

-2

-1

0

1

2

3

4

5

6

Y-Axis Acceleration

Seconds

Metres/S

econd

2

Data AnalysisY- Axis• Vertical• Impact

Z- Axis• Anterior-Posterior• Integration

X- Axis• Medio-Lateral

500 510 520 530 540 550 560 570 580 590

-1

-0.5

0

0.5

1

SamplesA

ccele

ration

Stride Counter

• Clear steps• Thresholding

technique• Stride• Distance = (Strides)

(Stride length)• Speed =

Distance/Time

Noisy Signals

• Common signal problem

• Inaccurate spike count

• Use distance between spikes

• Worse during faster run

6 6.5 7 7.5 8 8.5 9

-3

-2

-1

0

1

2

3

4

5

Acceleration

Seconds

Metr

es/S

econd2

Integrator

• Acceleration=>Speed=>Distance

• Area under curve• area 1 is the

previous sample • area 2 is a triangle

formed between the previous sample and the current one

Area = Previous Sample + | Sample-Previous Sample | 2

Data Correction

• Undesirable data (S & I)• Calibration (S & I)

• Filtering (I)• Averaging (I)

Undesirable Data• Unwanted NaN values• Use “isnan” to locate• Replace with average of nearest

neighbours

Calibration

• Average samples over the range• Subtract the offset from the data• Major accuacry improvements

Filtering Data• Set “no movement” states to zero• Use thresholding technique and

control variable• When variable is “1”, data is “0”

Averaging data

• Integration necesity • Window of 64 samples

Justification of Stride Counter

4 6 8 10 12 14-3

-2

-1

0

1

2

3

4

X: 13.54Y: 0.6195

Acceleration

Seconds

Metr

es/S

econd2

X: 3.6Y: 0.8255

0 5 10 15

-10

0

10

20

30

Averaged Acceleration

Seconds

Met

res/

Sec

ond2

0 10 20

-10

0

10

Averaged Acceleration

Seconds

Met

res/

Sec

ond2

0 10 20

-10

0

10

20

Averaged Acceleration

Seconds

Met

res/

Sec

ond2

Failure of Integrator

• Unsatisfactory results• Noisy Data• Purely Graphical information

3 speed

Steady

Stop inc.

Comparison of algorithms

Stride Counter• Simple• Highly accurate• Clean data• Limitations due to

manual user input requirements

Integrator• Unsuitable for

calculating abilities

• Graphical indicator of human movement

Problems Encountered

• Serial Port Issues• Programming Issues

• PDA Issues

Conclusion

The proposed aim of designing and developing a portable, cost effective accelerometer based personal trainer system was reached:

AccelerometerData Acquisition Processing algorithmsFeedback

Future Work

• Incorporate PDA• Stride Counter automation

• Energy Algorithm• Incorporate ECG

References[1] Information on Triaxial Accelerometers

http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=retrieve&db=pubmed&dopt=abstract&list_uids=9216127

[2] SparkFun forum

http://forum.sparkfun.com/search.php?mode=results [3] Useful bluetooth information

http://www.tech-faq.com/bluetooth.shtml[4] Useful background on labVIEW

http://en.wikipedia.org/wiki/LabVIEW[5] Background information on Matlab

www.mathworks.com [6] Signal processing for estimating energy expenditure of elite athletes using triaxial

accelerometersWixted, A.; Thiel, D.; James, D.; Hahn, A.; Gore, C.; Pyne, D.

Sensors, 2005 IEEEVolume, Issue, 30 Oct.-3 Nov. 2005 Page(s): 4 pp. -

Digital Object Identifier   10.1109/ICSENS.2005.1597820[7] Paper on position algorithm implementationFreescale semiconductor application note

Implementing Positioning Algorithms Using AccelerometersBy: Kurt Seifert and Oscar Camacho[8] Useful Information on Accelerometers

http://www.electronics-manufacturers.com/info/sensors-and-detectors/accelerometer-sensor.html  

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