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Arduino nano 33 BLE pressure sensor strange data
OK, I played a bit...

Main conclusion : when the IMU sensor is running (accelerometer, gyroscope, magnetometer), then the barometer gets some periodic dips. When the IMU sensor is not running, the dips do not appear. In the program that interfaces phyphox to the Arduino nano, all sensors are initialized in the setup, so that even if you run the "pressure" experiment, the IMU has been activated. When you delete the initialization of the IMU (loosing the possibility of running the accelerometer, gyroscope and magnetometer), the pressure experiment works just fine.

I stripped down the program to only these two sensors, I even get rid of the BLE connection and used the serial cable to get the data, and the effect is still here. The only difference between the two graphs below is the following line in the setup of the arduino nano setup() function:

  if (!IMU.begin()) {
    while (1);

So the dips come from an interaction between the barometer and the IMU sensor. I guess I should post a question on the Arduino forum about that...

Note that the frequence of the dips is different (1s instead of 6s when I did the test on my smartphone). Stripping down the program and getting rid of the BLE did have some effect...

If anyone has some insights on the origin of these dips...



Thank you, Fred, for researching this issue. Indeed weird…

I just posted a question on the arduino forum about this problem, since it is not a phyphox question. Here is a link:

Meilleurs Regards,

Some more to this feature... I have modified the program to switch IMU sensors on at 50 seconds after the acquisition start. I observe with my Arduino  a reduction of the noise and a step of the signal. I will try to add this to the Arduino forum.
How have been your boards powered while testing? Battery (What kind) or USB (portable charger, power supply, …)?
The board is powered by USB..

New test:  IMU.begin() at 35 sec and IMU.end() at 70 sec...

Attached Files
.pdf   pressure_via_python2(2021-09-03).pdf (Size: 26.07 KB / Downloads: 337)
Just a quick note that the problem of measuring pressure from the barometer with activated IMU sensors has been resolved in the Nano 33 BLE Sense Rev2. The new board is equipped with two IMU sensors (BMI270 - 6 axis and BMM150 - 3 axis) instead of one on the old board (LSM9DS1 - 9 axis). There are no jumps in the pressure readings anymore.
Ah, that is great news, thank you for testing and posting !



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