BMX055 Accelerometer Fast Compensation and Magnetometor Data Interpretation

[GMASCIARDT]

Hello,

I'm using the BMX055 IMU in an accessory for motorcycles. I started testing the IMU in our first prototype and I'm successfully able to read the data of ACC, GYRO and MAG via I2C. 

However there are a couple of things that are not so clear to me:

1) I followed the procedure for the ACC fast compensation described at page 31-32 of the datasheet, that is:

     - set the g range to 2g (write 0x03 in register ACC 0x0F)

     -  Set offset target for x, y and z, that in my case are x=0, y=0 and z=1g (write 0x20 in register ACC 0x37)

     - Launch the calibration for x, y and z, that is, write in register ACC 0x36 the value 0x20, 0x40, 0x50, respectively

 but it seems that it has no effect. Am I doing something wrong?

2) I'm not sure how to interpret the X, Y, Z and RHALL data of the MAG for a compass-like application. Is there any data processing/compensation I need to do? I took a look at some drivers/APIs on GitHub and I noiticed that there is a compensation. The thing is that the registers used to get the compensation values appear to be marked as "reserved" on the datasheet. Could you please clarify that?

Thank you in  advance!

[o_o]

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@GMASCIARDT wrote:

1) I followed the procedure for the ACC fast compensation described at page 31-32 of the datasheet, that is:

     - set the g range to 2g (write 0x03 in register ACC 0x0F)

     -  Set offset target for x, y and z, that in my case are x=0, y=0 and z=1g (write 0x20 in register ACC 0x37)

     - Launch the calibration for x, y and z, that is, write in register ACC 0x36 the value 0x20, 0x40, 0x50, respectively

 but it seems that it has no effect. Am I doing something wrong?

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First of all I just noticed a tiny mistake i the datasheet. Section 5.4.1 is actually slow compensation (high-pass filter). Make sure you follow the steps for section 5.4.2. there is also an application note on this: https://ae-bst.resource.bosch.com/media/_tech/media/application_notes/BST-MAS-AN030.pdf

The effect depends on how large your initial offset is. Read back the values of the registers. If they are non-zero then the compensation is active

[o_o]

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@GMASCIARDT wrote:

2) I'm not sure how to interpret the X, Y, Z and RHALL data of the MAG for a compass-like application. Is there any data processing/compensation I need to do? I took a look at some drivers/APIs on GitHub and I noiticed that there is a compensation. The thing is that the registers used to get the compensation values appear to be marked as "reserved" on the datasheet. Could you please clarify that?

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This is the API you want to use : https://github.com/BoschSensortec/BMM150-Sensor-API

The trimming registers are marked as reserved in the datasheet, customers must use the API. See section 9.3.2 of the datasheet