I purchased 2 of the new DIY Drones Rev 1.1HMC5843 boards back in late NOV.
The data I'm get from them seems to have way too much "jitter".
With the magnetometers stationary and flat and level:
unit 1's readings vary by 54 count in X, 57 counts in Y and 62 counts in Z
unit 2's readings vary by 103 counts in X, 110 counts in Y and 102 counts in Z
when I apply the POSITIVE BIAS (unit still stationary, flat and level) the readings vary by:
unit1 75 counts X, 64 count Y and 109 counts Z
unit2 143 counts X, 170 counts Y and 194 counts Z
by vary I mean: for example readings range from 750 to 607 (unit 2 +BIAS CAL) 750-607 = 143
The i2c comm seems to be working as I can change modes, output rate etc.
But the variance of reading when sitting still seem WAY out.
I can't obtain meaningful scale factors or offsets with the readings jumping around so much.
Has anybody seem this problem or have any suggestions as to what's wrong.
Any help would be appreciated.
Thanks,
James
attached are raw data files for unit1 and unit2
in each data file:
1st group of readings are with the magneto stationary flat and level pointing approx 130 deg
2nd group is with positive bias applied
3rd group is with negative bias applied
Replies
Hi Jim,
the magnetometer is actually very very sensitive to magnetic noise. You should check if there are sources for magnetic noise in the vicinity. Try to toutput the HMC readings from another computer. They should vary +/- 5.
However, the difference between your 2 units in not explicable this way.
From when are these chips actually? I know there had been an issue with the chips from 2009 production which could be fixed by adding an external capacitor. Search in the sparkfun forum for this issue.
Andreas