How to calibrate the sensor

[juwei80]

Hello Scott,

Do you have a sample of using the set_acceleration_bias correctly to calibrate the sensor?

Thank you.

[storborg]

I don't, sorry. I implemented the API layer but haven't really gotten familiar with the sensor much yet. I would speculate, though, that you want to do something like:

1. Leave sensor stationary for some period of time (so that filters have settled)
2. Set the acceleration offset to zero
3. Poll the acceleration values
4. Set the acceleration bias to negate the received acceleration values

I think there might also be some auto-calibration functionality in some of the models.

[juwei80]

In the witmotion software (Win) theres a Accel calibration button which is doing the magic I am looking for.
I want to have the same by using python, but don't know how.
If I set the acceleration value presented by the device (multiplied with 1000 as integer since it requires an 16 bit integer) to set_acceleration_bias, I get close to zero but I think I am doing it the wrong way... There must be a much more effective and reliable way I guess.

The auto-calibration seems to be the way I am looking for, but the methods aren't doing anything.

Is there an official API description available which you have used for developing the API?

[storborg]

I've used these two documents:
https://drive.google.com/file/d/1MEI7tDrXXUmLWrQpdVaytGN_O8nbJ2U9/view?usp=sharing
https://drive.google.com/file/d/1G9pWDA5nB9uXNM3DummGCKelPZVeMqSt/view?usp=sharing

Linked from here:
https://www.wit-motion.com/9-axis/witmotion-hwt905-rs232-high.html

Also, I've only run this code against an HWT905, perhaps there are some differences with the bluetooth-capable product.

I don't have a sensor on hand at the moment, but I'll try to test the next chance I get.

[juwei80]

Ah, thank you for pointing to the datasheet.
I've found the following on the BWT61CL page 16.
Looks like the registers differ from HWT905, so that's the reason why only few commands work with the BWT61:

6.2 Config Commands
Instruction content   Function                        Remark
0xFF 0xAA 0x52        Angle initialization            Z-axis to 0
0xFF 0xAA 0x67        Accelerometer Calibration       X,Y axis to 0

With that information I just made it to calibrate the X and Y axis:

    # send to calibrate X,Y
    imu.ser.write(
        struct.pack(
            "<BBB",
            0xFF,
            0xAA,
            0x67
        )
    )