accelerometer jitter

[Michael Fisher]

On Sat, Sep 20, 2008 at 4:07 PM, Joel Newkirk <freerunner at newkirk.us> wrote:

> I wrote a short shell script to repeatedly take the raw output from one of
> the accelerometers (/sys/devices/platform/spi_s3c24xx_gpio.1/spi0.1/dump)
> and massage the data to output X,Y,and Z-axis readings in decimal, -128 to
> 128.
>
> With my Freerunner sitting flat, face up, on the concrete slab of my house,
> the 'Z' reading (positive Z is toward the back of the handset, BTW)
> fluctuates between 51 and 56. (X and Y range from -1 to 2)  That's a
> variance of +/- 5%, and I'm fairly confident gravity isn't fluctuating
> significantly... ;)
>
> Is that to be expected, is my Freerunner defective, or am I doing something
> wrong?
>
> I'm trying to develop a simple tool that will determine 'down' based on
> output from the accelerometer, and indicate deviations from various
> 90-degree orientations - will I need to massage the data further to ignore
> variations, should I be averaging several readings, or what?
>
> j
>
>
>
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j

As a bit OT but since you have gone to the trouble of developing the script,
could you run a test while driving/riding in the car and post what the
readings might be? I was thinking of the possibility of having the FR
determine if it was in a moving car or not.

Mike

-- 
Michael Fisher
desNotes at gmail.com
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