EVAL-ADXL346Z Analog Devices Inc, EVAL-ADXL346Z Datasheet - Page 30

• 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

ADXL346
A double-tap event can also be invalidated if acceleration above
the threshold is detected at the start of the time window for the
second tap (set by the window register (Address 0x23)). This results
in an invalid double tap at the start of this window, as shown in
Figure 47. Additionally, a double-tap event can be invalidated if
an acceleration exceeds the time limit for taps (set by the DUR
register (Address 0x21)), resulting in an invalid double tap at
the end of the DUR time limit for the second tap event, also
shown in Figure 47.
Single taps, double taps, or both can be detected by setting the
respective bits in the INT_ENABLE register (Address 0x2E).
Control over participation of each of the three axes in single-tap/
double-tap detection is exerted by setting the appropriate bits in
the TAP_AXES register (Address 0x2A). For the double-tap
function to operate, both the latent and window registers must
be set to a nonzero value.
Every mechanical system has somewhat different single-tap/
double-tap responses based on the mechanical characteristics of
the system. Therefore, some experimentation with values for the
TIME LIMIT
TIME LIMIT
FOR TAPS
FOR TAPS
(DUR)
(DUR)
Figure 47. Tap Interrupt Function with Invalid Double Taps
Figure 46. Double-Tap Event Invalid Due to High g Event
LATENCY
(LATENT)
TIME (LATENT)
TIME
LATENCY
When the Suppress Bit Is Set
DOUBLE TAP AT
INVALIDATES
END OF DUR
TIME LIMIT
FOR TAPS
(DUR)
SECOND TAP (WINDOW)
TIME LIMIT
FOR TAPS
TIME WINDOW FOR
INVALIDATES DOUBLE TAP IF
TIME WINDOW FOR SECOND
(DUR)
INVALIDATES DOUBLE TAP
SUPRESS BIT IS SET
AT START OF WINDOW
TAP (WINDOW)
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DUR, latent, window, and THRESH_TAP registers is required.
In general, a good starting point is to set the DUR register to a
value greater than 0x10 (10 ms), the latent register to a value greater
than 0x10 (20 ms), the window register to a value greater than
0x40 (80 ms), and the THRESH_TAP register to a value greater
than 0x30 (3 g). Setting a very low value in the latent, window, or
THRESH_TAP register may result in an unpredictable response
due to the accelerometer picking up echoes of the tap inputs.
After a tap interrupt has been received, the first axis to exceed
the THRESH_TAP level is reported in the ACT_TAP_STATUS
register (Address 0x2B). This register is never cleared but is
overwritten with new data.
IMPROVED TAP DETECTION
Improved tap detection is enabled by setting the improved tap
bit of the TAP_AXES register (Address 0x2A). When improved
tap detection is enabled, the filtered output data corresponding to
the output data rate set in the BW_RATE register (Address 0x2C)
is processed to determine if a tap event occurred. In addition, an
ac-coupled differential measurement is used. This results in the
timing values and threshold values for improved tap detection
being different from those used for normal tap detection.
When improved tap detection is used, new values must be
determined based on test results. In general, no timing values
(in the DUR, latent, or window registers) should be set that are
less than the time step resolution set by the output data rate.
The threshold value for improved tap detection can typically be
set much lower than the threshold for normal tap detection.
The value used depends on the value in the BW_RATE register
and should be determined through system testing. Refer to the
Threshold section for more details.
TAP SIGN
A negative sign is produced by experiencing a negative accel-
eration, which corresponds to tapping on the positive face of the
device for the desired axis. The positive face of the device is the
face such that movement in that direction is positive acceleration.
For example, tapping on the face that corresponds to the +X
direction, labeled as front in Figure 48, results in a negative sign
for the x-axis. Tapping on the face labeled as left in Figure 48
results in a negative sign for the y-axis, and tapping on the face
labeled top results in a negative sign for the z-axis. Conversely,
tapping on the back, right, or bottom side results in positive
signs for the corresponding axes.
Figure 48. 3D Orientation with Coordinate System
+x
FRONT
(+X)
+z
TOP
(+Z)
LEFT
(+Y)
+y