compass module

[aruna1]

Hi
I'm thinking of buying a compass module for my robots
cheaper one will be better.

I have no idea what are the things i should consider when buying a compass.
can someone help me here
thank you

[waltr]

What are your requirements for the Compass?
Just a heading on level terrain?
Or do you need a heading with the Bot tilted?

SparkFun carries several:
http://www.sparkfun.com/search/results?term=compass&what=products

I have used the Compass Module - HMC6352 with reasonable success.
http://www.sparkfun.com/products/7915

[aruna1]

well most of time it would be used on flat terrain.anyway much of tilt this can compensate? I mean evan we thought terrein is flat it can be laces we cant identify

[aruna1]

Hi can i use this as a compass? its cheaper than sparkfun
http://cgi.ebay.com/Dual-axis-Magnetic-Sensor-Module-UART-I2C-0-359-/350418221692?pt=LH_DefaultDomain_0&hash=item51968dba7c#ht_4406wt_957

[waltr]

I guess you could if it is fully documented. It does have a UART (asynchronous data) which is a little easier to interface to a uController than the I2C used by the other compass modules.

[aruna1]

Hi
I have attached datasheet here
http://www.sure-electronics.net/download/down.php?name=DC-SS504_Ver1.0_EN.pdf
can you please take a look at this?

[waltr]

Well the data sheet does look to be complete. A couple of things to note:
1- It seems that the UART interface is only used to initialize calibration and set the local magnetic deviation and is the only way to do these functions.
2- To read the magnetic data I2C must be used. The data sheet seems to explain how to do the I2C sequence in detail.
3- The SET & RESET of the magnetic sensor elements must be done by the Master processor (its not automatically done internally by the compass)

[aruna1]

so in that case this sensor (without i2c) (more cheaper than previous) will also do the trick right?
I mean with both sensors I have to use I2C

and what is this dual axis thing?
http://cgi.ebay.com/Dual-axis-Magnetic-Sensor-Module-2-c-Interface-/230558944655?pt=LH_DefaultDomain_0&hash=item35ae624d8f

[UAE]

I have never used them before but I'm planning to use them and I was reading a lot on them

From what I understood,

It depends on your application
there are 2(dual)-axis and 3-axis compasses and it depends on your application

If you are going to use it on a flat terrain then 2-axis will be good

If you may use them on rugged terrains (sand, grass, eg.), a 2-axis compass might give you inaccurate data because of the tilts and in this case you might need a 3-axis compass