A Tri-Axial Accelerometer Interface For The
Transmission Of Impact Measurements
Figure 1 [1]
Figure 2 [2]
Heather Marandola SUNFEST 2000
Advisor: Jim Ostrowski
General Athletic
Accelerometer Applications
Figure 3 [3]: Rowing Application
Figure 4 [4]: Hockey Application
The Accelerometer
• What is an accelerometer?
• Defining Characteristics
– ‘g’-rating
– sensitivity
– axes
• Choosing the proper accelerometer
Entran 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
[7]
[8]
Period =
Rset ( W )
125MW
[9]
Noise ( rms ) =
[6]
d ia
500 mg
Hz
x
BWx1.5
f
[10]
F( 3dB) = 1
5mF
( 2 p( 32 kW ) xC ( 2 ,3)) =
C ( 2 ,3)
Accelerometer Data Evaluation
67 Degree
Pendulum
67 Degree
ImpactSwing
4
4
SetupData
ZeroExperimental
Acceleration Raw
4 x 10
x 1 07
4.5
4 x 10
x 10 7
5.2
6
B
B
B
A
x 10
C
4
5
D
4.8
x 10
C
C
2
5
E
Accelerometer
attached to a block
at the end of the
E
pendulum rod,
D
axes oriented
as shown
4
4.6
6
3
Vcc5
2
E
4.4
C
4
4
C
Vcc
1
D
A
4
0
GND
D
E
4.2
1
0
0
200
400
3
0
D
B
B
4
7
D
3.5
GND
C
B
Vcc B
A
7
6
B
B
6
5
4
A3
B
B
5
4
B
500
1 0 0 03
1500
600
reading
2000
800
1000
1200
0
200
400
3.8
2500
3000
3500
4000
4500
GND
0 3
500
1000
1500
reading
600
reading
2000
2500
800
3000
3500
1000
4000
reading
1200
4500
‘A’ indicates the release point of the pendulum
A
B
y impact with the wall
‘B’ indicates the point
of the
first
x
‘C’ indicates the point of the second impact with the wall
‘D’ indicates the point
of the
third impact with the wall
C
D
‘E’ indicates the pendulum’s recoil period
2
1
0
2
500
1000
1500
reading
2000
2500
3000
1
0
500
1000
1500
reading
2000
2500
3000
Accelerometer Data Evaluation (cont.)
Calibration Test
0.6
2.5
0.4
2
1.5
1.5
0.2
A
1
A
0
1
-0.2
g’s
0.5
g’s
D
1.5
1
g’s
0.5
-0.4
-0.6
D
B
0
g’s
0.5
A
0
0
A
C
-0.8
-0.5
-1
-0 . 5
-0.5
-1.2
-1
0
50
100
150
-1
200
reading
250
300
350
0
50
100
150
reading 2 0 0
-1
250
300
350
B
-1 . 5
C
4
100
0
200
-1.5
300
400
500
0
600
6
100
200
2
300
400
500
600
reading
reading
4
0
‘A’
‘B’
‘C’
‘D’
2
‘A’
-2
x
-4
g’s
y
g’s
x
-6
y
y
x
-8
x
y
0
x
-2
y
-4
-10
-12
0
50
100
reading
150
200
250
-6
0
50
100
reading
150
200
250
Display Mechanism
Acceleration Display Mechanism
Display
0
0*
0**
“
0********************
Overload
Acceleration Range (g’s)
0 to .25
.25 to .75
.75 to 1.25
“
9.75 to 10.25
> 10.25
Transmission & Reception
Linx Technologies LC Series Wireless Data Modules
315 Hz Transmitter:
315 Hz Receiver:
[11]
Benefits:
• low cost
• low power consumption
• very compact
[11]
[11]
Other Transmission Considerations
• Choosing an Antenna
The “Splatch”
0.062” thick
(easily concealed)
[12]
• Data Encoding
The Scenix
Microcontroller
[13]
Transmission/Reception Eval Boards
Scenix
Programmer:
Scenix
Programmer:
In from
PC (Sxkey)
In from
PC (Sxkey)
GND
GND
Vcc
Vcc
RF in (ant)
GND
GND
GND
GND
Vcc
GND
GND
VccVcc
Vcc
Vcc
Vcc
GND
GND
GND
x-in into
Data out from receiver,
microcontroller from accelerometer
y-in
Data out from microcontroller,
into transmitter
RS232 Communication
Transmitting the #1:
S 1
0
0
0
0
0
0 0
S
PIC
PIC
PC
ACCEL
TX
RX
Transmitting the
x-zeroing
data
acquisition value (42265) and the y-zeroing value (42489)
conversion from
and
RS232
The
four byte serial output to be sent is: series to parallel
communication
1010010111111001 (x-accel) 1010010100011001 (y-accel).
S 1 000 1 1 1 1 SS 1 0 1 00 1 0 1S S 1 00 1 1 000 S S 1 01 00 1 0 1S
1st x-byte
2nd x-byte
1st y-byte
2nd y-byte
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.
References
1. http://www.exploratorium.edu/hockey/checkig1.html
2. http://members.tripod.com/Yale_Football/yale.html
3. http://www.analog.com/industry/iMEMS/markets/consumer/sports_training/sports_tr.html
4. http://www.geocites.com/SunsetStrip/Palms/2366/ozolinsh.html
5. http://www.entran.com/ega.htm
6. http://www.analog.com/industry/iMEMS/products/X1210eb.pdf
7. http://www.analog.com/pdf/ADXL210_10_b.pdf
8. 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.html
12. http://www.linxtechnologies.com/f_antenna.html
13. http://www.scenix.com/tools/parallax.html