Understanding accelerometer data

Neil Jerram neiljerram at googlemail.com
Thu Oct 29 22:36:42 CET 2009

I'm struggling to understand my accelerometer data.  Here's what I
see, opening and reading the /dev/input/event[2,3] files every 4
seconds, when my FR is flat on its back on the table.

(event2 -36 54 198)(event3 -72 108 234)
(event2 -36 54 198)(event3 -72 90 234)
(event2 -36 54 198)(event3 -72 108 252)
(event2 -36 54 198)(event3 -72 108 234)

I'd expect the x and y values to be much smaller than the z values
(compared to the ratios here) because of the z value including
gravity.  Am I misunderstanding what the data is telling me?

To put it another way, if I accept that the z values here do mean 1g,
it looks like there are x and y accelerations going on of between 0.1g
and 0.5g - which is unexpected given that the FR is not moving.

Thanks for any enlightenment!


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