BMA253
Data sheet
Page 29
4.7.5 Slope / any-motion detection
Slope / any-motion detection uses the slope between successive acceleration signals to detect
changes in motion. An interrupt is generated when the slope (absolute value of acceleration
difference) exceeds a preset threshold. It is cleared as soon as the slope falls below the
threshold. The principle is made clear in figure 7.
acceleration
acc(t0)
acc(t0−1/(2*bw))
time
slope(t0)=acc(t0)−acc(t0−1/(2*bw))
slope
slope_th
time
slope_dur
slope_dur
INT
time
Figure 7: Principle of any-motion detection
The threshold is defined through register (0x28) slope_th. In terms of scaling 1 LSB of (0x28)
slope_th corresponds to 3.91 mg in 2g-range (7.81 mg in 4g-range, 15.6 mg in 8g-range and
31.3 mg in 16g-range). Therefore the maximum value is 996 mg in 2g-range (1.99g in 4g-
range, 3.98g in 8g-range and 7.97g in 16g-range).
The time difference between the successive acceleration signals depends on the selected
bandwidth and equates to 1/(2*bandwidth) (t=1/(2*bw)). In order to suppress false triggers, the
interrupt is only generated (cleared) if a certain number N of consecutive slope data points is
larger (smaller) than the slope threshold given by (0x28) slope_th. This number is set by the
(0x27) slope_dur bits. It is N = (0x27) slope_dur + 1 for (0x27).
Example: (0x27) slope_dur = 00b, …, 11b = 1decimal, …, 4decimal.
BST-BMA253-DS000-01 | Revision 1.0 | August 2015
Bosch Sensortec
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Note: Specifications within this document are subject to change without notice.
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