Help with 5883L crazyness.

Question

I have collected data and cannot get it to point to the correct heading. Its off quite a bit and I cannot adjust as the amount it is off is non-linear. For example, at 0 degrees it shows 100 degrees. But at 45 degrees it shows 170 degrees. Z axis is level and remain constant for the most part.

Here is the data I collected, does it makes sense? I used a compass on my phone and compared to the readings I am getting.

0 degrees North
X 0
Y 155
Z -530

Calculated heading: 100

90 degrees east

X -165
Y 100 (shouldn't this read 0 since it is pointing in same direction X was just at?)
Z -530
Calculated Heading: 224

180 degress South
X: 0
Y: -290
Z: -540

Calculating Heading: 286

270 degrees West

X: 250
Y: -100
Z: -550
Calculated Heading: 252

One thing I am thinking is odd, if at 0 degrees north X axis reads 0, if I rotate 90 degrees to right, would Y axis now read 0?

I am not sure what the axis is measuring, I thought it was force and it I point x axis in one direction, then Y axis in same direction, they would show the same reading...

X and Y are 90 degrees in parallel plane.
I ordered another magnometer hoping a different brand will help. Its still 5883L but different maker of breakout.

jw0752 · Answer

Is there a correction factor necessary for the angle of the Earth's magnetic field in your area?

The Data Sheet mentions a calibration factor that can be calculated using the self test.

HMC5883L 18 www.honeywell.com SCALE FACTOR CALIBRATION

Using the self test method described above, the user can scale sensors’ sensitivity to match each other. Since placing device in positive bias mode (or alternatively negative bias mode) applies a known artificial field on all three axes, the resulting ADC measurements in data output registers can be used to scale the sensors. For example, if the expected self test value for X-axis is 766 and the actual value is 750 then a scale factor of (766/750) should be multiplied to all future readings of X-axis. Doing so for all three axes will ensure their sensitivity are well matched,

The built-in self test can also be used to periodically compensate the scaling errors due to temperature variations. A compensation factor can be found by comparing the self test outputs with the ones obtained at a known temperature. For example, if the self test output is 750 at room temperature and 700 at the current temperature then a compensation factor of (750/700) should be applied to all current magnetic readings. A temperature sensor is not required using this method.

John

Help with 5883L crazyness.

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