Compass bearing by Telemetry - LSM303 module

I have been making some progress with using this module, which has given me problems in the past. The key thing is to make sure that you run the calibration routine for the Arduino regularly. (Not getting the full 0 to 360 degrees is a sure sign of this.)

I have installed the LSM303 with its own Arduino and 16x2 LCD screen in a "water tight" box:



The watertight box is something of an overkill but it was  good 3D printer practise! (It still needs an epoxy resin coating for water-tightness.)

The compass reading goes as an i2c interface to the telemetry (also gives depth and battery voltage) Arduino via a 1m cable. (Still getting some transmission problems with this. Garbage appears on the screen after a few seconds.)

David

Hi David,

Are you using i2C Bus Pullup Resistors?

Is your LSM303 an Adafruit, Pololu or something else?

Are you using i2c for the LCD screen?

Do you get the same issue with garbage data if you run the boards example code?

Perhaps run the i2c scanner to confirm addresses of hardware...

Regards
Jonathan

the original telemetry dingus i made that is/was documented over on subpirates used a pololu device that was a 3d compass and accelerometer to compensate for tilt in any direction...  it ran right next to the arduino pro micro, which was 2 inches from the receiver, and gave me reasonably accurate heading for the hour or so that i ran the sub at a regatta in california a few weeks after i built it.

sadly, i haven't been keeping up on the telemetry side of things, and that dingus has been sitting in a drawer since i got back from that regatta...

the exact part is still available from pololu:

https://www.pololu.com/product/2127


I may be assuming too much, but i would think that is what david is using..

I have used various "compass" boards and found them all a bit frustrating apart from this one - CMPS11 ( now CMPS12) - Whilst expensive it is a solid as a rock.

I notice having pasted the link that this is version 4 CMPS12 which I have not used.

http://www.hobbytronics.co.uk/cmps-12-tilt-compass

The CMPS12 has onboard Kalman filter's  - I can't remember the exact spec of the CMPS11 but if had an onboard buffer of some 25 reads or so to smooth the output

Thanks for the advice Tim and Jonathan.

The LSM303 IS a Pololu.

I have fitted 4.7k pullup resistors to the i2c bus which also has the LCD connected.

The i2c scanner shows the compass Arduino address but only intermittently.

It is looking like a cable fault (I am using 1 m of audio coax) but your suggestion to run the example software is a nice one.

I have also tried  a Honeywell compass module HMC5883L but that never gave good readings - maybe calibration issues again?

I have found compass modules tricky. They work so well in phones!

It is one of the few sensors which works underwater though.

Thanks again,

David

Hi David,

All part of the fun!

I have been playing with a display for my telemetry. In it's early stages but designed to run via wifi on most web browsers so could be on a phone/tablet/pc

No real data yet - just beginning to explore the concept



Regards
Jonathan

I am not using pullup resistors, but as i said, there MIGHT be 2" of wires between the compass module and the arduino. I was able to run the example arduino sketch, and the calibration sketch with zero issues.

I have given up on using the LSM303 in my submarines. It works well on the bench but once you get it into the close confines of a model submarine it stops giving reliable readings. I did try calibrating it "in situ" but this really didn't help.

I also tried feeding it via its own dedicated arduino  but this just made things more complicated.

If you have a very large submarine you may able to find a remote location for the compass module (I was looking to use the waterproof box shown earlier.) but it really starts getting too complicated for only a "nice to have" (compass reading by telemetry.) It will work nicely in surface ships , I think.

On the plus side the 3D printed waterproof box seems to work well. I waterproofed the box by painting the interior with  5 minute epoxy (The "Pound Shop" tube variety.)

I plan to now use the box for some Pinger  R & D!

David

Doh - senior moment - I realise I had already posted about this device - sorry

David,

I have used this compass (below) is several models - works a treat.

Expensive - yes - but look at the detailed spec and see what's under the hood!!!

I love the fact that it has an onboard 45 read sampling buffer to smooth the output

http://www.hobbytronics.co.uk/cmps-12-tilt-compass?keyword=compass

and the detail

http://www.robot-electronics.co.uk/files/cmps12.pdf

Regards
Jonathan