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 W5PFG

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Clayton, 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 - https://www.adafruit.com/products/2472

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.

Steve KD8QWT

On Thu, Feb 18, 2016 at 1:58 PM, Clayton W5PFG w5pfg@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 W5PFG

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Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb