SCA3000 Series
7. Acceleration data is not available when the SCA3000 is in motion detection mode
8. The INT-pin is activated when motion is detected in the X- or Y-axis direction (Z-axis
direction is ignored), see section 2.7 for detailed INT-pin information.
2.4 Free-Fall Detection
2.4.1 Description
During free-fall in the gravitation field, all 3 orthogonal acceleration components are ideally equal to
zero. Due to practical non-idealities, detection must be done using Threshold Level (TL) greater
than 0.
When enabled, the Free-Fall Detection (FFD) will monitor 8 MSB's of the measured acceleration in
the X, Y and Z directions. If the measured acceleration stays within the TL longer than time TFF
(Figure 4 below), which corresponds approx 25 cm drop distance, the FFD will generate an
interrupt to the INT-pin.
Acceleration
X, Y and Z
+TL
T1
T2
T3
T4
T5
T6
T7
T8
Time
-TL
TFF
INT output
"1"
"0"
T1
T2
T3
T4
T5
T6
T7
T8
Time
Figure 4. Free Fall condition.
2.4.2 Usage
Free-fall detection can be enabled by setting FFD_EN bit in MODE register to "1". See section 3.4
for MODE register details.
Acceleration data is available in registers X_LSB, X_MSB, Y_LSB, Y_MSB, Z_LSB, Z_MSB and
BUF_DATA as in measurement mode. See section 3.3 for output register and section 2.7 for
interrupt functionality details.
2.4.3 Example
A simple example of free-fall detection usage:
1. Write "00010000" (10h) into the MODE register (enable free fall detection, FFD_EN = '1')
2. Acceleration data can be read normally
3. INT-pin is activated when free fall is detected, see section 2.7 for detailed INT-pin
information.
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