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MPU-9250 instead of MPU-9255?
#1
Hi Sean,

Finally the IMU arrived, but now it appears to be a 9250 instead of a 9255...
Does it work with the MPU-9250? Or do I have to make modifications for that?
Currently the heading is very unstable, is there a calibration procedure?

regards
Hans Fix
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#2
Yes, both IMUs work.

https://docs.sailoog.com/openplotter-v1-...alibration
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#3
(07-17-2018, 02:12 PM)Sailoog Wrote: Yes, both IMUs work.

https://docs.sailoog.com/openplotter-v1-...alibration

Thanks Sailoog,

I am using the Pypilot image of Sean, does that have the same calibration feature?
(I can see the level calibration, and there is a button 'lock calibration')

regards
Hans
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#4
you can lock the calibration with tinypilot as well.

I recommend upgrading pypilot to latest git. I think openplotter 1.0 doesn't have the latest calibration fixes.

Would it be useful to "upgrade pypilot" similar to "upgrade opencpn" in the menu?
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#5
Yes, it is.
Latest calibration fixes were added in openplotter v1.1.0
I will add any change you make in every major update.
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#6
I don't think it is a calibration issue. I connected it to a rpi3 with an openplotter image that i dowloaded yesterday. First i had the same problems there. Than I added two pull ups of 3k3 on the i2c lines, and it all became stable.
Sadly enough not for the rpi zero.. that remained unstable.
So I continued testing on the rpi3 which went well untill 5 minutes ago, than it became unstable again. After rebooting it was stable again.
Do the i2c interfaces use different speeds on the two devices? Can I switch it to a lower speed?
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#7
After some measurements on i2c: communication seems to be ok. there was a wrong connection with pull ups, but that didn't cause the problems.
Also suspected a capacitor which was not soldered correctly, but that doesn't seem to improve it either....
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#8
I believe the speed is 100khz. If you have issues with i2c connection, it is most likely hardware.
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#9
Hi, I 've put the oscilloscope on it, and the signals seem to be ok, from the power supply there was a small spike, but with an other power supply the results were the same.
So still strange why it is working on the Rpi with open plotter and not on the tiny pilot image.

I think, I will wait for a new IMU sensor, and see what happens with that one...
(After some changing between the two boards, the thing is not working at all any more, although it is detected by the Rpi-Pypilot as a MPU-9250/MPU-9255 ....)
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#10
If it works with openplotter it should work with tinypilot because the driver is the same.

There is a bug in tinypilot that if you change to a different sensor, it won't work. If you delete RTIMULib.ini it will work again. I will correct this soon, I am currently working on supporting more sensors. the library may technically detect them and give data, but many sensors need to calibrate the accelerometer bias unlike mpu925x.

The new mpu9255 with orange (not yellow) capacitor also need accelerometer bias calibrated, so beware of this. Currently I have some that have bias so far wrong (more than 1 g) that they saturate the 2g range even when perfectly still. This needs additional work to automatically switch to 4g range in the driver, and will lose a bit of precision (which should be ok)

So at the moment I suggest only mpu9250/mpu9255 with yellow capacitor or otherwise factory calibrated accelerometer (range .098 to 1.02 g) but I will support other sensors soon, and it requires additional calibration for accelerometer bias.
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