HMC5883L Magnetometer chip Possibilities.

[gunayburak]

if the device is held so that the xy plane is perfectly!!!! level then the xy angle is magnetic north (sort of). if the device is tilted then the xy angle needs to compensated for that tilt . the device alone cannot really be used as a compass . the device output is a 3d vector as drawn by the black line in my previous post, as you can see the result is relative to the devices orientation , if that is unknown (and it is without an external reference ) then its virtually impossible to ascertain a direction from its output. even a small tilt creates substantial error.
furthermore magnetic field lines are not parallel with the earths surface they tilt into the earth or up to the sky depending on location. not to mention magnetic inclination/deviation etc
basically the concept of using this chip as a compass is unworkable see post 47

That was a nice a explanation Richard ... As you've previously said , we can at least use this IC to observe the pitch then ... For example I'm intending to read XZ or YZ to see the pitch angle for the control of an inverted pendulum ... I personally thought it's a low cost way of doing it compared to an encoder ... Bye the way .. For my module , should I keep it horizontally flat just like in the picture or upside down , does it matter ?

Here is my module

[richard]

For example I'm intending to read XZ or YZ to see the pitch angle for the control of an inverted pendulum ... I personally thought it's a low cost way of doing it compared to an encoder

not sure how effective that will be , it would probably need to be calibrated every time you relocate it (or maybe even rotate it) . don't forget its own orientation is its only reference point . an accelerometer might be more appropriate

[gunayburak]

Well , Yeah actually I'm planning to calibrate it right before every operation with a quick push button click ... So that It can assume the present values as exact zero .. It's all about math I guess .... I'm also aware of that It won't be that accurate ... But I still wanna use it ... Thanks for your all prompt answers Richard ...

[towlerg]

For example I'm intending to read XZ or YZ to see the pitch angle for the control of an inverted pendulum ... I personally thought it's a low cost way of doing it compared to an encoder

Surely what you need is an accelerometer, you know that the period is always the same, it just moves faster when first set in motion (I'm not totally sure that's correct, my knowledge of basic physics is pretty ragged). If that's correct, there will be a relationship between angle and acceleration. With calibration you should end up with a look up table of acceleration/angle. Of course you'll only need to generate the table once.

Also I cant imagine how you would orient the magnetometer to even hint at the angle.

BTW anyway, you couldn't use an encoder if you want the pendulum to be "true", pivot must be frictionless.

Sounds like an interesting project, have fun.

George