[PSUBS-MAILIST] compass

Wed Oct 31 11:00:39 EDT 2018

Alan,
For the most part, it's about accuracy.  This device has been around for many years, it's true, but that's because the specs are very good.  It also performs all the calculations spitting out compass heading, yaw, pitch, in a directly usable format as well as being tilt compensated up to 60 degrees (I think).  It can be mounted in three different planes which isn't so important from a PSUBS perspective but could be critical in some applications.  So for basic compass purposes it is definitely a Cadillac.
There are many cheaper solid state compasses available but few are tilt-compensated and even a little bit of tilt has a major impact on the measurement output.  The tilt-compensation on the HMC-6343 really works well and it was important to me to know that the output I am seeing is as accurate as possible despite any wave action on the surface, or small balance issues under water.
Any IMU with 9 degrees of freedom can be used to accomplish the same thing but they all output raw data that needs to be calculated, twisted, torqued, torched, hacksawed, and then welded back together again.  The HMC-6343 does that all internally and is simple to configure and program.
The link I showed is a Canadian outlet so price is $188(CAD).  USA suppliers have them for $159(US) although they go into short supply occasionally.  Add on an arduino for $35 and a bit of time programming, and you have a nice accurate compass for less than $200(US).
I have mine mounted in a small 1 inch PVC pipe with caps on both ends.  I will probably fill it with epoxy but I suspect the 1-ATM pvc will hold up fine for the depths I'll be at.  And yes, it will be mounted externally, probably 3 feet or so away from the metal hull.  However, with programming I can filter any deflection offset caused by the metal hull.
Jon

      From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Tuesday, October 30, 2018 10:46 PM
 Subject: Re: [PSUBS-MAILIST] compass

Jon,I have to buy a compass some time so looked it up but it's pretty expensiveat $188-. I also saw a video on it dated 2010, so it's at least 8 years old.There are modules for less than $20- but not tilt compensated.It does say it is "high end" but is there much difference between a cheap& expensive compass? ( I know nothing about this).The thought came to mind that you could possibly cover it with resin &mount it outside the hull away from magnetic interference.Alan 
On 31/10/2018, at 1:36 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hank,
I use HMC6343 tilt compensated compass from Honeywell, with arduino or Raspberry pi microprocessor.  Display can be in many formats.  These are sometimes hard to get but looks like CANAKIT has some.
Compass with Tilt Compensation - HMC6343

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Compass with Tilt Compensation - HMC6343
 Compass with Tilt Compensation - HMC6343  |   |

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      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: irox via Personal_Submersibles <personal_submersibles at psubs.org> 
 Sent: Monday, October 29, 2018 10:48 PM
 Subject: Re: [PSUBS-MAILIST] compass

 Ian, Thank you, sorry about the sharp bracket.  I will mount the new one on a plastic pole behind the CTHank
    On Monday, October 29, 2018, 6:43:07 PM MDT, irox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

Hi Hank!
you could google for "Fluxgate compass" and see what you're comfortable with from an electronics point of view.
You could build your own for ~$50 ($15 for compass, ~ $10 for microcontroller, ~$20 for a display):https://www.adafruit.com/product/1120
But I imagine you'd prefer something more turn key, like:https://www.starmarinedepot.com/clipper-compass-system-w%2Fremovable-fluxgate-sensor.html
The sensor would need mounted outside, away from the hull, like a regular compass.
Cheers!  Ian.P.S.:  Please make it less sharp that the current compass mounting bracket on Gamma. :-)

-----Original Message-----
From: hank pronk via Personal_Submersibles 
Sent: Oct 29, 2018 5:23 PM
To: Personal Submersibles General Discussion 
Subject: [PSUBS-MAILIST] compass

Hi All,It is time to deal with a compass for Gamma.  I would like a solid state compass with no moving parts.  Jon, I think you mentioned I could do something for 200 dollars?  Any ideas are welcome.Hank
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