[Gta04-owner] Making sense of the sensors.

Benjamin Deering ben_deering at swissmail.org
Thu Aug 9 02:12:54 CEST 2012

I played a bit with valacompass on GTA04.  Libsensmon would need a 
BMA150 module for tilt compensation to work, but I commented out the 
accelerometer code in my build.

The hmc5843 driver for the latest SHR kernel has the sysfs files in a 
different place.

I changed .Sensmon/config to include:

The sysfs file 'rate' seems to have changed to sampling_frequency.

X,Y,and Z values come from separate files.  I'm not a vala programmer, 
but I can send what I did to get them.

I had to adjust in_magn_range to get the Y axis to show anything but -4096.0

I don't know how important the tilt compensation is, but with all my 
changes the needle in valacompass does not point north.  The direction 
it points seems to change when I rotate the phone, but it is very 
noisy.  I think there is some interference from the speaker magnets as I 
was able to get a reading on the Y axis without adjusting the range if I 
brought a magnet near the phone.  I have Slyon's 3d printed speaker box 
and 2 speakers, maybe those with a single speaker will have different 


On 08/04/2012 02:10 PM, Michele Brocco wrote:
> On 8/4/12, NeilBrown<neilb at suse.de>  wrote:
>> The compass seems to have a strong bias on all axes. Presumably some magnet
>> in the GTA04 (speaker?) needs to be compensated for.  Has anyone played
>> with
>> this at all?  Figured out how to calibrate, then how to convert the 3
>> numbers
>> into  a compass direction?
> hi neil,
> I wrote a proof of concept user space compass application for the
> navigation board (http://wiki.openmoko.org/wiki/ValaCompass). you can
> take a look at the source code if you want. i wanted to update the
> application once the kernel in shr will support this sensor and the
> accelerometers. but currently I am very busy and could not chek if
> everything is there already.
> regards,
> Michele
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