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ADXL210 View Datasheet(PDF) - Analog Devices

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ADXL210 Datasheet PDF : 11 Pages
1 2 3 4 5 6 7 8 9 10
ADXL202/ADXL210
STRATEGIES FOR USING THE DUTY CYCLE OUTPUT
A DUAL AXIS TILT SENSOR: CONVERTING
WITH MICROCONTROLLERS
ACCELERATION TO TILT
Application notes outlining various strategies for using the duty When the accelerometer is oriented so both its X and Y axes are
cycle output with low cost microcontrollers are available from
parallel to the earth’s surface it can be used as a two axis tilt
the factory.
sensor with a roll and a pitch axis. Once the output signal from
the accelerometer has been converted to an acceleration that
USING THE ADXL202/ADXL210 AS A DUAL AXIS TILT
varies between –1 g and +1 g, the output tilt in degrees is calcu-
SENSOR
lated as follows:
One of the most popular applications of the ADXL202/ADXL210
Pitch = ASIN (Ax/1 g)
is tilt measurement. An accelerometer uses the force of gravity
Roll = ASIN (Ay/1 g)
as an input vector to determine orientation of an object in space.
Be sure to account for overranges. It is possible for the acceler-
An accelerometer is most sensitive to tilt when its sensitive axis
ometers to output a signal greater than ± 1 g due to vibration,
is perpendicular to the force of gravity, i.e., parallel to the
earth’s surface. At this orientation its sensitivity to changes in
tilt is highest. When the accelerometer is oriented on axis to
gravity, i.e., near its +1 g or –1 g reading, the change in output
acceleration per degree of tilt is negligible. When the accelerom-
eter is perpendicular to gravity, its output will change nearly
E 17.5 mg per degree of tilt, but at 45° degrees it is changing only
at 12.2 mg per degree and resolution declines. The following
table illustrates the changes in the X and Y axes as the device is
tilted ± 90° through gravity.
T +90؇
Y
E X
0؇ 1g
–90؇
L X AXIS
ORIENTATION
TO HORIZON (؇)
X OUTPUT
Y OUTPUT (g)
PER
PER
DEGREE OF
DEGREE OF
X OUTPUT (g) TILT (mg) Y OUTPUT (g) TILT (mg)
O –90
–75
–60
–45
S –30
–15
–0
15
30
B 45
60
75
O 90
–1.000
–0.966
–0.866
–0.707
–0.500
–0.259
0.000
0.259
0.500
0.707
0.866
0.966
1.000
–0.2
0.000
4.4
0.259
8.6
0.500
12.2
0.707
15.0
0.866
16.8
0.966
17.5
1.000
16.9
0.966
15.2
0.866
12.4
0.707
8.9
0.500
4.7
0.259
0.2
0.000
17.5
16.9
15.2
12.4
8.9
4.7
0.2
–4.4
–8.6
–12.2
–15.0
–16.8
–17.5
shock or other accelerations.
MEASURING 360؇ OF TILT
It is possible to measure a full 360° of orientation through grav-
ity by using two accelerometers oriented perpendicular to one
another (see Figure 15). When one sensor is reading a maxi-
mum change in output per degree, the other is at its minimum.
Y
X
360؇ OF TILT
1g
Figure 15. Using a Two-Axis Accelerometer to Measure
360 ° of Tilt
Figure 14. How the X and Y Axes Respond to Changes in
Tilt
REV. B
–9–
 

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