design and development of an accelerometer based personal trainer system by emer bussmann b.e....
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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
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
Data Acquisistion Unit -LabVIEW suitability-
• Visual programming language • Libraries – functions• Polymorphism • Access of instrumentation hardware
– Serial Communication VI• PDA research
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
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”
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
Conclusion
The proposed aim of designing and developing a portable, cost effective accelerometer based personal trainer system was reached:
AccelerometerData Acquisition Processing algorithmsFeedback
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