accelerometer jitter

Joel Newkirk freerunner at
Sat Sep 20 22:07:02 CEST 2008

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

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

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?


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