My accelerometers aren't calibrated.

Andy Green andy at
Wed Nov 26 12:55:26 CET 2008

Hash: SHA1

Somebody in the thread at some point said:
| Mateusz Kondej wrote:
|> Hi,
|> I think that accelerometers in my FR aren't calibrated or driver doesn't
|> work properly. For example, if I use script form
|>, I got this
|> data:
|> X	Y	Z	SUM
|> 54 -18 -1062 1063
|> 54 -18 -1062 1063
|> 36 -18 -1062 1062
|> 54 -18 -1062 1063
|> 54 -18 -1044 1045
|> 36 -18 -1080 1080
|> FR is laying on my table, screen to bottom. So it should return gravity,
|> 981 cm/s^2. But It returns similar values but it's too big for me.
|> How to get properly results from accelerometers? Eventualy How to
|> calibrate them?
| I'm wondering, why the LIS302DL kernel driver returns 16bit values for
| each axis. Because the sensor itself has only 8bit resolution for each
| axis. The next question is if the returned values are normalized to
| "g * 10^-2" or just upscaled raw values (which makes no sense). Because
| 1g in 8bit would be ~64 if the sensor is set to +-2g range (which can be
| changed to +-8g range within the sensor).
| When the returned values are representing "cm/s^2" than you are right
| that the z-value is a bit off.
| But i can't find any related information about how to interpreted the
| returned x/y/z axis values on the wiki page.

It's in mG, the actual 8-bit values are worth 18mG each typically for
that chip.  1000 is 1G then.

So the "calibration" for the original poster is fairly decent allowing
that 1 count is worth 18 and the sensor values change according to exact
mounting detail of PCB to plastic, amount of solder paste under each
side of it, how level his floor and table are, etc.  There's an extra
~80 on 1 full G because his single sample on that device is not exactly
18 but 17.9x, but we don't take care about it.

- -Andy
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