[amsat-bb] Remote sensor for antenna array orientation

Zach Leffke zleffke at vt.edu
Thu Feb 18 20:50:50 UTC 2016

Hi Clayton,
     I used an accelerometer for elevation feedback and a magnetometer 
for azimuth feedback as part of a system that drove arrow style antennas 
on a PTZ camera mount that did not have any feedback sensors built in.  
All purchased at sparkfun (or adafruit can't remember) and driven by an 
arduino atmega328p using (basically the arduino Uno, there was also 
reference arduino code for getting the things up and running on the 
website I bought them from).

I wrote up and published the circuit design for that system in the 
proceedings of the 2013 symposium.  If you need a copy of the paper I 
can probably dig it up from wherever I saved it.

My experience with it was that the accelerometer was rock solid for tilt 
or elevation feedback.

The magnetometer on the other hand was shall we say 'finicky.'  It did 
work for my purposes, but required re-calibration frequently, and 
re-calibration basically every time you moved the set up to a new 
location.  It also had pretty noisy measurement data where the angle 
reported by the device would 'bounce around' even when the sensor was 
stationary.  So I had to play games with the arduino to keep a running 
average of the feedback to smooth out the noisy feedback.  Also, the 
accuracy of the magnetometer data was decent but not great.  If you have 
something like an arrow antenna with a fairly broad beam, then it was 
good enough, but if you need "precision pointing" then the magnetometer 
is probably not the way to go.

All of my experiences were based on a pretty cheap device from spark 
fun.  It could be that cell phone technology has caught up and something 
that you can get on those websites for cheap is more robust than the 
sensor I used.

Hope this helps,

-Zach, KJ4QLP

Research Associate
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

On 2/18/2016 1:58 PM, Clayton W5PFG 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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