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4.2.2.1 Motion Detector
Fig. 22 shows the Z-axis acceleration data. Obviously, in Fig. 22, Section 1,
Section 3 and Section 5 are when the device is not moving and Section 2 and 4 are when
the device is in motion. The key of the motion detector is to distinguish between Section
1, 3, 5 and Section 2, 4.
In order to explain this algorithm, Section 1 will be zoomed in as shown in Fig. 22.
The evident difference between ‘motion’ section and ‘stop’ section is that in Section 1
almost all the samples are in a certain range, in this case, [-0.25g 1 -1.25g]. On the
contrary, in Section 2, a large amount of samples are not in [-0.25g -1.25g]. Since in each
cycle the program could only reload 20 ~ 22 samples, first the number of samples that are
not in [-0.25g -1.25g] are counted and then divided by the total number of samples to
calculate the percentage. If 85% of the samples are not in [-0.25g -1.25g], which means
the object is in Section 1, 3 or 5. Otherwise it is not.
1
1g = 9.81 m/s2
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