FSM#8: How to… test your FSM – Free fall, another algorithm example

[Eleon BORLINI]

This example describes how to set up a finite state machine to enable the built-in detection of the Free Fall. The picture here below shows the steps of the dedicated FSM. The algorithm is able to detect the free fall of an object generating an interrupt if e.g. the z-axis acceleration falls below a certain threshold (e.g. 0.4g).

Input data are the axl output (select ODR >= 26Hz)

Mask selects as interesting orientation axis the overall resultant directions v+, v- (0x03)

Thresholds can be set to 0.4g

Timeout selectable (e.g. 0x03 = 120 ms, that simulates the time duration of the free fall)

Output is an interrupt when a free fall acceleration profile is detected for 120msec

Enjoy!

Link: https://www.st.com/content/ccc/resource/technical/document/application_note/group0/56/95/d6/a1/34/4c/49/6d/DM00517282/files/DM00517282.pdf/jcr:content/translations/en.DM00517282.pdf