Thingy91: Problem with motion detection using ADXL362

[WaStefan]

Hello everyone,

I am currently using the Nordic-Thingy-91 to test the nRF9160 and other components on the board.
Now I am trying to implement a simple motion detection with the low power accelerometer ADXL362.
The goal is a simple state information, if the board is moving or not.

The strange thing is, it works in all cases, except when the Thingy91 lies flat (= -1g on Z axis).
In all other maximal positions (1g on X, -1g on X, 1g on Y, -1g on Y, 1g on Z) it detects the lack of motion correctly.
In the case of -1g on Z it does not detect inactivity.

I have implemented the motion detection according to the ADXL362 datasheet. Here is my configuration:

• Range: +-2g
• Absolute activity/inactivity detection in Loop-Mode
• Active threshold set to 1200
• Inactive threshold set to 1100
• Inactive time set to 24 (~4sec)
• ADXL362 operating in Wakeup mode
• Mapped AWAKE bit to INT1, which I monitor with the controller

I have read back all the registers to make sure the values are written correctly and they are.

I have also tried "Referenced" activity/inactivity detection as it is described in the datasheet (Application examples, page 36),
but I could not make it work. It just didn't detect inactivity.

As I said before, it works nicely in all cases, except when Z = -1g, then it doesn't detect inactivity.

Has anyone encountered this problem before?
Or has anyone implemented a stable and working motion detection?

ADXL362 Silicon revision id: 3

Thank you!

[JONATHAN LL]

Hi,

Could you  share your code, I can test it out on a couple of thingy91 to see if the problem persist on different HW versions.

Regards,
Jonathan

[WaStefan]

Sure, here you go.

MotionDetection.zip

It is a simple application that sets the LEDs according to the motion state.

- Red: Unknown state (should never happen)
- Green: Moving
- Blue: Still, not moving

[JONATHAN LL]

Pardon for taking so long to get back,

What NCS version did you use for this project? Hawing some trouble getting it to run properly.  Do you have a hex file i could test ?

Regards,
Jonathan

[WaStefan]

I use 1.5.

Here are two .hex files, I don't know which one you need, so here you have both ^^

2677.merged.hex

0523.zephyr.hex

[JONATHAN LL]

Was able to build and successfully flash a Thingy91(v1.4.0) with your code and your code seems to work perfectly fine, when not connected to a USB to see what comes out on the terminal everything seems to work as you described. The device turns green when i move it and once placed regardless of orientation it turns blue within some seconds.  If i do have it connected via USB  it seems to be a bit finicky and does not seem as reliable,  it takes a couple of tries but it turns blue when left alone eventually. 

You can check the version of your Thingy91 by looking at the sticker, underneath the PCA number. 

Regards,
Jonathan

[WaStefan]

I also have a Thingy91 with v1.4.0.

I was able to achieve the same results as you did. It really seems that a connected USB cable affects the accelerometer data!

When I connect the cable it doesn't work properly as described in the original post. But when I remove the cable it works fine... strange ^^

But thank you for your help and your tip with the USB connection!