[amsat-bb] Remote sensor for antenna array orientation

Steven Kalmar pista01 at gmail.com
Sun Feb 21 18:42:02 UTC 2016

I've been experimenting with 9-DOF boards for a custom AZ/EL rotator and
controller build I'm doing.  DOF chips require filtering to reduce the
noise levels of the raw data and to calculate a heading.  Even with
filtering, the values tend to bounce around a lot, by more than a few
degrees.  They also need to be calibrated by moving them around.  Obviously
this is an issue when it's mounted to a rotator as you can't easily move it
around when powering it up.  Some DOF libraries will allow calibration data
to be saved and re-applied after restart.  The noisy data and processing
required for the filters has been the main issues for me.

I just received this one from Adafruit -

It has an onboard processor that filters the raw data and returns absolute
position in degrees, with no math on the Arduino and no bouncy readings.
Once the board is calibrated and the calibration setting saved, it's just a
matter of loading the saved calibrations when the board powers up.

I haven't had this board long enough to determine how well it will work
long term, but so far I've been impressed with it's noiseless and
consistent readings over many restarts.  It even returns a consistent
compass heading when it's pointing north and it's rotated 90 degrees along
the E/W axis..  The previous board I tried didn't do so well for compass
readings when the board wasn't flat.  My plan is to use this to calculate
compass and elevation from it's boom mounted position for initial rotator
zeroing and as a secondary sensor for sanity checking AZ/EL positions.


On Thu, Feb 18, 2016 at 1:58 PM, Clayton W5PFG <w5pfg at amsat.org> wrote:

> Has anyone ever mounted a mutli-axis accelerometer or a magnetic compass
> sensor to their antenna crossboom for making adjustments to point of aim?
> I'm currently using Hall Effect sensors but experiencing several degrees
> of drift over a short period of a few days.
> 73
> Clayton
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