Open Source AHRS project: giving away hardware

Pascal Gosselin pascal at
Mon May 12 04:21:10 CEST 2014

On 2014-05-11, 11:28 AM, joerg Reisenweber wrote:
> This all assumes a locked and defined mounting situation for the magnetometer.
> Then yes. For an embedded device however this method tells you nothing about
> the magnetometer heading. The embedded device can change relative orientation
> to the vehicle that's driving.
> PS: you must be very sure about the vehicle moving exactly straight ahead as
> well, for anything but a non-sliding car that's not guaranteed, think boat,
> even airplane

We're talking calibration here.  Yes the unit should be rigidly mounted 
for calibration of the sensors.  There are also periods of "stay still 
for X seconds" at various points in such a calibration.   I have done 
and continue to do lots and lots of AHRS calibrations of various types 
on aircraft (airplanes and helicopters).  I would be more than happy to 
share the information that I have on various calibration techniques.

Once the sensors are calibrated (i.e. figuring out the drift of the Rate 
Gyros when sitting still) and the magnetic environment of the device is 
known, what's left is the alignment procedure. Every time you start the 
AHRS code on the device, it would need to be motionless for a while.  
Lying the GTA02/GTA04 flat on a table for example for perhaps 2-3 
minutes might be sufficient.

I feel that this likely the reason why even the latest mainstream phones 
don't have AHRS or IMU capability (an IMU would enable indoor navigation 
over only very short distances in a smartphone, given the rather crude 
quality of the MEMS sensors and horrific gyro drift expected if you are 
bouncing around with the smartphone in your hand and moving rather 
slowly without GPS aiding the Kalman filter).

Application for an AHRS on a smartphone would be for enhanced 
geo-referencing of photos and "Google Glass" type applications that 
don't make you look like a Glasshole.  The other obvious application is 
as an emergency backup attitude (Pitch and Roll) and Heading indicator 
for airplanes and helicopters.... or simply recording of the sensor data 
and doing post-processing on a server to process the data later (think 
extreme sports, like playing back a skydive for example).


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