Ted YapoThere has been some activity over on GitHub about the MLX90393 Arduino driver, and it caused me to take another look at the datasheet. Guess what? They changed it! The scaling parameters are different now, which makes the output more accurate. I had to revive my Helmholtz coil to test it.
The new scaling factors and a previously undocumented HALL_CONF field (hall effect configuration?) field, which selects 2- or 4-phase hall plate spinning, are in the code and being tested. After a bit more mileage, I'll merge them into master. So far, the results are encouraging:
You can see the scaling numbers in the new datasheet are much closer to the calculated magnetic field in the Helmholtz coil (about 10% high). I previously measured the coil against the Earth's field and estimated it to be within 2%, so there's room for improvement, but it's getting closer!
The temperature compensation for the part is still mysterious and doesn't seem to work for me. I'll have to dig into the new version of the datasheet a little more closely to look for clues.
Temperature compensation appears to be working, as long as you remember to set the offsets relative to 0x8000.
At one point, I figured out how to get accurate offset values using a modified compass calibration algorithm. I'll have to revisit and publish it.
Discussions
Become a Hackaday.io Member
Create an account to leave a comment. Already have an account? Log In.
Hi Ted! Great project!!
I did a 3D magnetic field scanner several years ago, so for me this project is really interesting. My goal was to use it to detect permanent magnets in electronic devices, as well to characterize the permanent magnets that I fabricated during my Phd thesis. I'd suggest you to scan a credit card magnetic stripe or a magnetic ticket such as the underground one (In spain it still have a magnetic band). Now i'm working in other things, always related to magnetism....
At the moment i'm working with the MLX90393, and I would like to know if you have been playing with resolution and gain of the sensor. I have some problems because, when the gain is changed the reading jumps... for instance, if the reading at Gain = 0 is 5uT, changing it to Gain = 1 gives a reading of 15uT. However, if resolution is changed the reading still the same, discarding an error in the conversion operation,
How are settings you are using for this calibration?
In addition, it would be nice to know the intensity of the magnetic field generated by the on-chip coil in the z-axis for calibration purposes....
Thanks in advance and hope to be in contact with you to discuss all you need about the magnetic field scanner!
Are you sure? yes | no