LIS331 Implementation

groufosse · ‎2013-10-04

Posted on October 04, 2013 at 16:39

Hello,

I'm hoping to get a bit of guidance here on this application I'm developing using the LIS331HH device.

I have integrated it into the application PCB, and using SPI to communicate with the device. All is well and I can set and read registers, ODR, filters, range, etc. Also, for actual implementation, I have tied the 2 HW interrupt lines to the microcontroller and will be using that in future. For the time, I just want to understand how to implement the right code to deliver the desired outcome. Using some test code, I can see data coming from xL, XH, yL, yH, zL, ZH but don't fully realize how to apply it for the desired outcome.

The application is very straightforward; to measure forces on the PCB that are primarily in 1 axis. After looking at a handful of code samples (there are few to be found) it's gained some clarity but still not there. Also, I didn't find the app notes helpful in terms of actual code implementation.

I understand that the orientation of the device is quite relevant to the data output. The PCB when installed in the assembly can ''roll'' (in x-y) about the Z-axis (meaning Z axis is horizontal relative to me)

So exactly what do I need to do with the output data to meaningfully use it? Here are some questions I hope someone can answer for me:

1 - The range of the device is +/-24g. Can I extend this to just +48g? How?

2 - How do I ''normalize'' the actual position relative to the absolute (calibrated) position and apply this to the data of interest?

3 - I'm primarily interested in the Z force vector. I also understand that there may be relevant applicable forces from x,y contributing to z, as the device rolls about on the z axis. Can I use the simple square root of sum-of-squares to tabulate total force on Z?

I would be mostly appreciative of a code sample, algorithm or clear explanation for this objective.

Thank you, regards,

Gary

#lis331

Thiago REIS · ‎2013-10-22

Posted on October 22, 2013 at 15:11

Hello Gay,

Please check the answers to your questions below:

1 - The range of the device is +/-24g. Can I extend this to just +48g? How?

- This is not possible the maximum FS available in this accelerometer is +/- 24g.

2 - How do I ''normalize'' the actual position relative to the absolute (calibrated) position and apply this to the data of interest?

- I am not sure what you meant by normalize, but you can set up an average to determine your product initial's positioning, and then develop your solution based on that reference.

3 - I'm primarily interested in the Z force vector. I also understand that there may be relevant applicable forces from x,y contributing to z, as the device rolls about on the z axis. Can I use the simple square root of sum-of-squares to tabulate total force on Z?

- I believe the Z-axis of the accelerometer already gives you a good idea of what is going on with the z-forces, that is because the sensor computes each axis indenpendetly, so, if you tilt your product, then, the x - y and z values will show a variation due to that movement.

ST does offer a tool for evaluation that can help you on your development, the Unico plataform that you can find on the link below:

http://www.st.com/web/en/catalog/tools/PF257815

Please do let me know if there is anything else that I can do to support you?

Thank you very much,

Thiago