Building my own Digital Solid-state Compass

[Flyboy]

I'm interested in making a digital compass that I can install on my truck, just for the fun of it. I've looked online and found some simple 8-point designs, which is probably suitable for what I have in mind, but it did raise the question: What would it take to make one capable of resolution on par with a typical airplane standby/"whiskey" compass, which is usually got for 1 degree resolution? Is it something that can be done at home and interfaced with an Arduino, or would it take specialist hardware?

 

[DaveE]

You can buy this in IC or development board format. Check the Adafruit, Sparkfun, MikroElektronika, Digikey, Amazon, eBay, etc. web sites.

I don't know about accuracy, this often depends on your calibration in SW because of nearby metals and such. It also raises some complex questions regarding the difference between accuracy, repeatability, resolution, etc. Even those whiskey compasses with no electronics require some calibration in situ. Boats, for example, often just have a table printed to show the deviation because really great calibration is a pain.

For the old school "steampunk" version, which you could really build from scratch, look into "flux gates", which is a magnetic device sort of like a transformer and some associated control circuitry. This is what you would find in electronic compasses before 1990, or so. These will be a bit difficult to get really good performance, so it's probably not the best way, but I think the underlying concepts are really interesting.

 

[DaveE]

BTW, TIL "whiskey compass" got that name because early compasses were filled with alcohol to keep them from freezing.

 

[berkeman]

I'm interested in making a digital compass that I can install on my truck

Sounds like a fun project. Have you done any mapping of your truck yet with a regular magnetic compass? I was very surprised at all of the error that I got when trying to mount magnetic compasses in my Explorer and Suburban SUVs. The middle of the front windshield seemed to have the least error, but it was still significant (and hard to null out with the simple adjustment that those compasses had at the time.

You might consider a little more advanced project where you use 2 GPS antennas to give you a lot more accurate compass reading...

https://oceannavigator.com/gps-compass/

 

[Flyboy]

You can buy this in IC or development board format. Check the Adafruit, Sparkfun, MikroElektronika, Digikey, Amazon, eBay, etc. web sites.

I don't know about accuracy, this often depends on your calibration in SW because of nearby metals and such. It also raises some complex questions regarding the difference between accuracy, repeatability, resolution, etc. Even those whiskey compasses with no electronics require some calibration in situ. Boats, for example, often just have a table printed to show the deviation because really great calibration is a pain.

For the old school "steampunk" version, which you could really build from scratch, look into "flux gates", which is a magnetic device sort of like a transformer and some associated control circuitry. This is what you would find in electronic compasses before 1990, or so. These will be a bit difficult to get really good performance, so it's probably not the best way, but I think the underlying concepts are really interesting.

I'll have to look into the dev boards. I'm just trying to understand how they arrange the senor(s) and what type of sensor it is.

Re: accuracy of standby compasses: Yeah, aviation ones have a correction chart, in 30 degree increments, and get recalibrated every so often. You take them out to a designated area and use a handheld "master compass" to guide the plane to point the right direction. Person inside the plane then takes note of the actual readings and will correct as needed. There's usually a couple of degrees of error at the 45s, i.e. NW, SW, NE, SE. Cardinal points are usually pretty spot on.

As for flux gates, I think I've got some stuff on them from my mechanic school books, as they're still used in some aircraft. I remember then being called flux valves, and they're very picky about what hardware you use to mount them and their inspection panels. Even tools have to be carefully selected.

BTW, TIL "whiskey compass" got that name because early compasses were filled with alcohol to keep them from freezing.

Yep! These days, it's a kerosene derivative, iirc.

Sounds like a fun project. Have you done any mapping of your truck yet with a regular magnetic compass? I was very surprised at all of the error that I got when trying to mount magnetic compasses in my Explorer and Suburban SUVs. The middle of the front windshield seemed to have the least error, but it was still significant (and hard to null out with the simple adjustment that those compasses had at the time.

You might consider a little more advanced project where you use 2 GPS antennas to give you a lot more accurate compass reading...

https://oceannavigator.com/gps-compass/

I haven't mapped anything yet. Was waiting to see what kind of accuracy was possible first before I got that detailed. And even then, I was planning on using the aviation approach of setting it up in an environment with minimal disturbances and pointing the truck at intervals, then taking note of the reading. I figured I could probably turn that into a table that an Arduino could use as a correction.

GPS might be a later addition. It's a bit more than I'm willing to dive into right now, but in the future could be handy. I've got some projects in the future that might need that.

 

[Borek]

Google for HMC5883L (just as an example).

 

[berkeman]

@Flyboy -- I saw the post below in my Facebook feed and it made me think of your project. How is it coming along?