A Tri-Axial Accelerometer Interface For TheTransmission Of Impact Measurements

Heather Marandola SUNFEST 2000Advisor: Jim Ostrowski

Figure 1 [1] Figure 2 [2]

General AthleticAccelerometer Applications

Figure 3 [3]: Rowing ApplicationFigure 4 [4]: Hockey Application

The Accelerometer

• What is an accelerometer?

• Defining Characteristics– ‘g’-rating

– sensitivity

– axes

• Choosing the proper accelerometerEntran Devices [5]

EGA Miniature Accelerometers(3.56 x 3.56mm to12.7 x 12.7mm)

The Evaluation Board

T2

T1 A( g) = (T1/T2 – 0.5)/12.5%0 g = 50% DUTY CYCLE

PeriodRset

M=

( )WW125

F dBk xC

FC

( )( ( ) ( , )) ( , )

3 12 32 2 3

52 3

==pm

W

Noise rmsg

Hzx BWx( ) .=

5001 5

md ia f[6]

[7]

[8]

[9]

[10]

Accelerometer Data Evaluation

Vcc

GND

VccGND

GND

Vcc

0 500 1000 1500 2000 2500 30001

2

3

4

5

6

7x 10

4

0 500 1000 1500 2000 2500 30001

2

3

4

5

6

7x 10

4

reading reading

Zero Acceleration Raw DataAccelerometer

attached to a blockat the end of the pendulum rod,axes oriented

as shown

Experimental Setup

xyA

C D

B

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 4 5 0 03

3 . 5

4

4 . 5x 1 0

4

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 4 5 0 03.8

4

4.2

4.4

4.6

4.8

5

5.2x 1 0

4

A

A

B

C

B

D

B

C

C

BB

D

B

B

D

B

C

B

D

B

reading reading

67 Degree Pendulum Swing

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 00

1

2

3

4

5

6

7x 1 0

4

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 00

1

2

3

4

5

6

7x 1 0

4

A

AB

B

CC

DD

E

EE

E

reading reading

‘A’ indicates the release point of the pendulum‘B’ indicates the point of the first impact with the wall‘C’ indicates the point of the second impact with the wall‘D’ indicates the point of the third impact with the wall‘E’ indicates the pendulum’s recoil period

67 Degree Impact

Accelerometer Data Evaluation (cont.)

0 100 200 300 400 500 600-1.5

-1

-0.5

0

0.5

1

1.5

0 100 200 300 400 500 600-1.5

-1

-0.5

0

0.5

1

1.5

g’s g’s

reading reading

A A

A AB

BC

CD

D

‘A’ ‘B’ ‘C’ ‘D’ ‘A’

x

x

xx

x

y y

y y

y

Calibration Test

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0-1

-0.5

0

0.5

1

1.5

2

2.5

g’s g’s

readingreading

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0-12

-10

-8

-6

-4

-2

0

2

4

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0-6

-4

-2

0

2

4

6

g’s g’s

reading reading

Acceleration Display Mechanism

Display Acceleration Range (g’s)0 0 to .250* .25 to .750** .75 to 1.25“ “0******************** 9.75 to 10.25Overload > 10.25

Display Mechanism

Transmission & Reception

Linx Technologies LC Series Wireless Data Modules

315 Hz Transmitter: 315 Hz Receiver:

Benefits:• low cost• low power consumption• very compact [11]

[11][11]

Other Transmission Considerations

• Choosing an Antenna

• Data Encoding

The “Splatch” 0.062” thick(easily concealed)

The Scenix Microcontroller

[12]

[13]

Transmission/Reception Eval Boards

Vcc

GND

Vcc GND

GND

Vcc

x-infrom accelerometer

y-in

GND

Vcc

GND

GND

Scenix Programmer: In from PC (Sxkey)

Data out from microcontroller,into transmitter

Vcc

GND

VccGND

GND

Vcc

Vcc

GNDGND

Scenix Programmer: In from PC (Sxkey)

Data out from receiver, intomicrocontroller

RF in (ant)

RS232 Communication

ACCELPIC

data acquisitionand RS232

communication

TX RX

PIC

conversion from series to parallel

PC

S 1 0 0 0 1 1 1 1 S S 1 0 1 0 0 1 0 1 S S 1 0 0 1 1 0 0 0 S S 1 0 1 0 0 1 0 1 S

1st x-byte 2nd x-byte 1st y-byte 2nd y-byte

S 1 0 0 0 0 0 0 0 S

Transmitting the #1:

Transmitting the x-zeroing value (42265) and the y-zeroing value (42489)The four byte serial output to be sent is:

1010010111111001 (x-accel) 1010010100011001 (y-accel).

Conclusions

• Preliminary filtering, scaling, & display mechanisms completed

• LC Series transmitter and receiver of sufficient caliber

• Transmission board capable of sending RS232 data across RF link

• Reception board capable of converting series to parallel

• Link must be established between the transmitter and receiver

The Future

Accelerometer applications within impact monitoring systems are numerous. I believe the future of this device

lies in the development of wireless interface system compatible with each of the applicable environments - a universal accelerometer interface requiring only minor

alterations when switching from one application to the next.

1. http://www.exploratorium.edu/hockey/checkig1.html2. http://members.tripod.com/Yale_Football/yale.html3. http://www.analog.com/industry/iMEMS/markets/consumer/sports_training/sports_tr.html4. http://www.geocites.com/SunsetStrip/Palms/2366/ozolinsh.html5. http://www.entran.com/ega.htm6. http://www.analog.com/industry/iMEMS/products/X1210eb.pdf7. http://www.analog.com/pdf/ADXL210_10_b.pdf8. http://www.analog.com/pdf/ADXL210_10_b.pdf (pg 7)9. http://www.analog.com/pdf/ADXL210_10_b.pdf (pg 8)10. http://www.analog.com/pdf/ADXL210_10_b.pdf (pg 7)11. http://www.linxtechnologies.com/f_modules.html12. http://www.linxtechnologies.com/f_antenna.html13. http://www.scenix.com/tools/parallax.html

References