ADXL346ACCZ-R2 datasheet(33/40 Pages) AD

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Data Sheet

ADXL346

codes. If V2 or V3 are set, their respective code is a valid

orientation. If V2 or V3 are cleared, the orientation of the

accelerometer is unknown, such as when the orientation is

within the dead zone between valid regions.

For 2D orientation sensing, the relation of the x- and y-axes to

gravity is used to determine the accelerometer orientation (see

Figure 50 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 50. These

regions also exist for landscape positive (+Y) and landscape

negative (−Y), as shown in Figure 50.

In 3D orientation, the z-axis is also included. If the accelerometer is

placed in a Cartesian coordinate system, as shown in Figure 49 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 49, 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

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

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.

PORTRAIT

POSITIVE (00)

NEGATIVE (01)

LANDSCAPE

POSITIVE (10)

NEGATIVE (11)

DEADZONES

Figure 50. 2D Orientation with Corresponding Codes

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 51. 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.

PORTRAIT

POSITIVE

LANDSCAPE

52.7°

45°

37.3°

POSITIVE

DEADZONE

Figure 51. Orientation Showing a 15.4° Dead Zone Region

By setting the INT_ORIENT bit (Bit D7) of the ORIENT_CONF

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.

Rev. C | Page 33 of 40

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