EVAL-ADXL346Z Analog Devices Inc, EVAL-ADXL346Z Datasheet - Page 33

• Manufacturer Part Number: EVAL-ADXL346Z
• Description: Inertial Sensor Evaluation System
• Manufacturer: Analog Devices Inc

Specifications of EVAL-ADXL346Z

• Silicon Manufacturer: Analog Devices
• Silicon Core Number: ADXL346
• Kit Application Type: Sensing - Motion / Vibration / Shock
• Application Sub Type: Accelerometer
• Silicon Family Name: IMEMS
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

For 2D orientation sensing, the relation of the x- and y-axes to
gravity is used to determine the accelerometer orientation (see
Figure 49 and Table 25). Portrait positive corresponds to the x-axis
being most closely aligned to the gravity vector and directed
upwards, opposite the gravity vector. Portrait negative is the
opposite of portrait positive, with the x-axis pointing downwards
along the gravity vector. Landscape positive corresponds to the
y-axis being most closely aligned with the gravity vector and
directed upwards, away from the gravity vector. Landscape
negative is the orientation opposite landscape positive. The
dead zone regions are shown in the orientations for portrait
positive (+X) and portrait negative (−X) of Figure 49. These
regions also exist for landscape positive (+Y) and landscape
negative (−Y), as shown in Figure 49.
In 3D orientation, the z-axis is also included. If the accelerometer is
placed in a Cartesian coordinate system, as shown in Figure 48 of
the Tap Sign section, the top of the device corresponds to the
positive z-axis direction, the front of the device corresponds to
the positive x-axis direction, and the right side of the device
corresponds to the positive y-axis direction.
The states shown in Table 26 correspond to which side of the
accelerometer is directed upwards, opposite the gravity vector.
As shown in Figure 48, the accelerometer is oriented in the top
state. If the device is flipped over such that the top of the device
is facing down, toward gravity, the orientation is reported as the
bottom state. If the device is adjusted such that the positive x-axis
or positive y-axis direction is pointing upwards, away from the
gravity vector, the accelerometer reports the orientation as front
or left, respectively.
The algorithm to detect orientation change is performed after
filtering the output acceleration data to eliminate the effects of
high frequency motion. This is performed by using a low-pass
filter with a bandwidth set by the divisor bits (ORIENT_CONF
register, Address 0x3B). The orientation filter uses the same
output data available in the output data registers (Address 0x32
to Address 0x37); therefore, the orient register (Address 0x3C)
is updated at the same rate as the data rate that is set in the
BW_RATE register (Address 0x2C). Because the output data
is used, the bandwidth of the orientation filter depends on the
value set in the BW_RATE register, and the divisor bandwidth
values in Table 24 are referenced to the selected output data rate.
To eliminate most human motion, such as walking or shaking, the
value in the divisor bits (Bits[D2:D0]) of the ORIENT_CONF
register (Address 0x3B) should be selected to effectively limit the
orientation bandwidth to 1 Hz or 2 Hz. For example, with an
output data rate of 100 Hz, a divisor selection of 3 (ODR/100)
results in a 1 Hz bandwidth for orientation detection. For best
results, it is recommended that an output data rate of ≥25 Hz in
normal power mode and ≥200 Hz in low power operation be used.
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The width of the dead zone region between two orientation
positions is determined by setting the value of the dead zone bits
(Bits[D6:D4]) in the ORIENT_CONF register (Address 0x3B).
The dead zone region size can be specified as per the values
shown in Table 24. The dead zone angle represents the total
angle where the orientation is considered invalid. Therefore, a
dead zone of 15.4° corresponds to 7.7° in either direction away
from the bisector of two bordering regions. An example with a
dead zone region of 15.4° is shown in Figure 50. It should be
noted that the values shown in Table 24 correspond to the
typical dead zone angle when the gravity vector is completely
contained in only two axes (xy, xz, or yz) and should be used
only as a starting point. If the device is oriented such that the
projection of gravity onto all three axes is nonzero, the effective
sensitivity is reduced, causing an increase in the dead zone angle.
Therefore, evaluation needs to be performed for specific appli-
cation uses to determine the optimal setting for the dead zone.
By setting the INT_ORIENT bit (Bit D7) of the ORIENT_CONF
register (Address 0x3B), an interrupt can be generated when the
device is placed into a new valid orientation. Only one mode of
orientation detection, 2D or 3D, can generate an interrupt at a
time. The orientation detection mode is selected by setting or
clearing the INT_3D bit (Bit D3) of the ORIENT_CONF register
(Address 0x3B). For more details, refer to the Register 0x3B—
ORIENT_CONF (Read/Write) section.
Figure 50. Orientation Showing a 15.4° Dead Zone Region
Figure 49. 2D Orientation with Corresponding Codes
+g
LANDSCAPE
+Y
POSITIVE
POSITIVE (10)
POSITIVE (00)
37.3°
+Y
+X
45°
52.7°
PORTRAIT
POSITIVE
PORTRAIT
DEADZONES
LANDSCAPE
+g
+X
DEADZONE
+X
+g
+Y
NEGATIVE (01)
NEGATIVE (11)
+X
+Y
+X
+g
+Y
+g
ADXL346