BNO085 calibration and performance

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gammaburst
 
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Re: BNO085 calibration and performance

Post by gammaburst »

Yes, an ordinary AC current meter is probably easiest, if you're careful near that 240 VAC.

I'm unfamiliar with the green Schneider clamp meter. Looks like an economy product. It measures AC current but not DC current. No mention of RMS so it probably measures Average. The datasheet doesn't say much. This Amazon page gives more specs and some customer reviews:
https://www.amazon.de/dp/B07JZ2V4BQ

Your small schematic has a problem. Based upon 11 W and 19 VA and 240 VAC, I estimate the degausser current to be roughly 80 mA AC. Imagine what will happen if you try to measure 80 mA using a 1 milliohm current shunt and an ordinary digital AC voltmeter.

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gammaburst
 
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Re: BNO085 calibration and performance

Post by gammaburst »

Back on Aug 7 you may have successfully degaussed your project. Do you need to worry anymore about the degausser? To confirm good degaussing and good magnetometer calibration, try physically rotating your entire BNO085 project to various orthogonal orientations (north south east west up down), and confirm that the three magnetometer readings remain approximately the same (of course the axes will rearrange and polarity may change).

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lumex
 
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Re: BNO085 calibration and performance

Post by lumex »

Hi,

Regarding the Pair if BNO performance and reproducibility
Yes the degaussed BNOs are now much more satisfactory.
Roll and pitch bias (between the two BNOs, which is a measurement of reproducibility) is very good : a few tenths of degree even with fast movements.
Yaw bias is low (remember that we started with tens of degrees with false north), when « status » (i.e. calibration accuracy) is 3. But higher than roll&pitch: approx +/- 4° and sign depends of the rotation clockwise or counterclockwise (like a screw).
This is not yet satisfactory. I need to make some tests to see if I can workaround this lack of accuracy for yaw.
I don’t specially need to know real heading but as I operate 2+ BNOs, I think I must use a reportType that makes fusion of acc+gyro+mag so they get yaw synchronized.

@jps2000: should I understand that it’s useless to play with tare and that we should just consider the option to force saving to flash memory of calibration data (that are automatically stored every 5 mn, or smth like that) ?
But depending on what?…


Regarding the measurements of AC current in the degausser
It’s interesting to complete that work.
And being able to degauss/gauss/degauss a board with high predictability and reproducibility.

Yes, 80 mA and a shunt resistor of 1mOhm will give a too small voltage!

As a conclusion, I understand that ordinary AC multimeter with current measurement will do the job. I’ll get a new one this week.

As a side work, I think that it’s very interesting to go on experimenting with a current clamp. Or with a home made Rogowski coil.

I didn’t find yet a 220V AC/220V AC coil transformer.

I tried to find a 220V/12V coil transformer to male a 220/12/220 isolation transformer.
But I just found a 220V/12V transformer (LED driver):
220V/12V transformer
220V/12V transformer
D5D13B1D-3B1A-41AA-A5CC-96A00B7E4E8C.jpeg (948.93 KiB) Viewed 169 times
This other model is claimed to be an electronic transformer.
220V/12V electronic transformer
220V/12V electronic transformer
34058C03-0B36-47D8-9C49-F6386435CC72.jpeg (720.42 KiB) Viewed 169 times
« Switch-mode » power supply?

I’m sure it’s not possible to reverse use that device to make a 220/12/220V transformer…
Is it correct?

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gammaburst
 
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Re: BNO085 calibration and performance

Post by gammaburst »

Hi lumex,
Again, the BNO085 datasheet says rotation vector accuracy is typically +/- 5 degrees. You observe +/- 4 degrees yaw error, so your BNO seems to be working as designed. If you need better performance, then the BNO085 is unsuitable and you need a better sensor. Or you could disable the BNO085's fusion firmware and write your own better fusion algorithm (good luck).

If you didn't find any isolation transformers, then you're shopping at the wrong place. However, I don't know your country's distributors. When I search DigiKey (USA) I find a hundred models in stock, and some are 230V:
https://www.digikey.com/en/products/fil ... AvKIw5UMyA

The "LED Driver" module is a DC power supply, not a transformer. You cannot reverse it.

The "ET-60-3" module looks like an ordinary step-down power transformer. Connecting two of them back-to-back should make a 230V-230V isolation transformer.

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lumex
 
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Re: BNO085 calibration and performance

Post by lumex »

Hi gammaburst,

Concerning the BNO accuracy
This is my main concern.
I forgot to mention that yaw bias is quite satisfactory but:
1/ after powering the system off and on, yaw bias becomes huge (say, 68°) and can keep on with that bias
2/ even when yaw bias is low (a few degrees, which is acceptable), yaw of each BNO is still strongly inaccurate (say, 20°, compared with a compass).

Doing eight-figures loops help getting good accuracy.

For unknown reason BNO nbr 2 is jumping -50 then BNO nbr 1 is jumping +50° while the system is in the same volume. Then going back toba 1-2° yaw bias and an individual accurate measure of yaw. That’s very surprising.

I believe at least that I may need to degauss again the BNO
The question is  « How much? When should I stop? ».
And is it the only problem?

I think we already discussed about measuring or testing the magnetic field around the BNOs.

Several ways (as far as I remember or imagine):
- use a hall effet sensor (I’ve bought one, successfully checked, that measures the mag field of a magnet ; I need to test it’s detection treshold for slightly magnetized objects)
- use a compass (the needle is my friend)
- use another magnetometer to detect mag field abnormalities

When I see this behavior with yaw, I wonder whether I really need to just use that « BNO black box » or if I need to manage something and how.

Concerning the isolation transformer (side concern)
I was in a consumer warehouse not specialized in such electrical devices.
The ET-60-3 module is an electronic transformer for powering LEDs. I don’t feel like it’s reversible, isn’t it ?
I’ve identified one isolation transformer I have to collect it.

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gammaburst
 
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Re: BNO085 calibration and performance

Post by gammaburst »

Yaw bias: Previous message you said "not yet satisfactory", now it's "quite satisfactory". Confusing.

Large yaw bias: Be sure you are using "rotation vector". Don't use "game rotation vector" or other special-purpose modes.

Large yaw jumps: The BNO085 doesn't output yaw, it outputs a quaternion. Is the quaternion jumping? Maybe the quaternion is good and the math conversion to pitch/roll/yaw is jumping somehow. (The older BNO055 has a math bug that causes large jumps in its yaw output.)

The ET-60-3 label doesn't say LED. It says 220-240VAC pri (primary), 11.6VAC sec (secondary), and lamp. That sounds like a simple transformer for powering 12V incandescent lamps. But if you don't think it'll work, don't buy it.

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lumex
 
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Re: BNO085 calibration and performance

Post by lumex »

Yaw bias
First, I confirm that roll and pitch are very satisfactory : good accuracy and very low bias, and very stable/reproducible day after day, as I'm playing with it.
Regarding yaw and yaw bias (between 2 BNOs), no it's not satisfactory. Because it's not stable. Hence sometimes it's quite satisfactory (low yaw bias : between +/- 2 and +/- 5° ; AND inaccurate yaw, say 20°), and sometimes yaw bias is crazy (not jumping measures, or jumping measures while moving a few cm).

Thanks for the idea to check quaternion values (even if the quaternionToEuler* fonctions are well known).
I've just programmed Serial and oled screen for displaying these measures
Result :
(r_bias, i_bias, j_bias, k_bias) is not (0.0, 0.0, 0.0, 0.0)
(r1, i1, j1, k1) being quaternion of BNO nb 1
(r2, i2, j2, k2) being quaternion of BNO nb 2

Rq: the 4 lines have a label "r". In fact it's r i j k ; column 1 is for BNO 1 and column 2 for nbr 2.
Last 2 lines are for (r_bias, i_bias, j_bias, k_bias).
---
quaternion_bias_measure_1.jpg
quaternion_bias_measure_1.jpg (224.04 KiB) Viewed 116 times
---
quaternion_bias_measure_2.jpg
quaternion_bias_measure_2.jpg (408.09 KiB) Viewed 116 times
---
I'm less used to quaternions than Euler angles, but we can see that i_bias and j_bias are near 0.0 (which should correspond to pitch bias and roll bias), while k_bias is not 0.0 (which should correspond to yaw bias). I don't exactly know what value should be for r.

Do you agree than the conclusion is "There is no problem with quaternionToEuler* fonctions" ?

"THIS pair of BNOs has a problem with yaw"...

EDIT
Here is another measurement. Labels are correct: r i j k and rb ib jb kb for bias measures.
Note that i and j are 0.0 .
quaternion_bias_measure_3.jpg
quaternion_bias_measure_3.jpg (337.56 KiB) Viewed 115 times
Isolation transformer
I really don't know about ET-60-3. If it was a coil transformer, I'm 100% sure that I can use two units to make a 220/12/220V isolation transformer. But I'm not competent to answer if a 220VAC/11.6 VAC "ELECTRONIC transformer" is reversible. Can I try to power it with 12 VAC and see it outputs 220 VAC at no risk for the component??

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jps2000
 
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Re: BNO085 calibration and performance

Post by jps2000 »

Hi Lumex,
First, quaternion vector sum is always 1. This is a good method to check validity of data.
In absolute orientation mode (rotation vector, 0x05 command in the BNO) it depends on the orientation which quaternions you get. They are very sensitive. So difference in angle can not be estimated just by looking at.
Of course you need to do warm up (>1min) and do calibration movements with both BNO together and then compare yaw pitch roll.
The BNO works best when there is continuous little movement. This is because gyro drift is compensated with accelerometer signals with a not disclosed method.
I would also like to see this heading estimation value the BNO is also sending. There should be a possibility to plot this as well.

Can you disclose what you like to do to need such a high yaw tracking accurracy?

An electronic transformer is NEVER reversable. DO NOT power the secondary with whatever.
ONLY a transformer with windings and iron core is suitable for step up or step down use and reversable. But it works ONLY with AC!!!!

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gammaburst
 
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Re: BNO085 calibration and performance

Post by gammaburst »

Hi lumex,

We may be experiencing "lost in translation" problems. We speak different native languages.

I see the quaternions in your LCD images, but why three images? Are they telling a story? The goal was to observe the quaternions to see if they jump like the yaw value. Perhaps I don't understand what you meant by "jump". To me, "jump" means the value (such as yaw) suddenly changes by a large amount even though you moved the sensor by only a small amount.

I don't know if quaternionToEuler is working properly for you. You are observing unexplained malfunctions, so everything is a suspect.

Have you tried running minimal example code that talks to only one BNO085? Does it work better, or do you still see yaw problems? On August 2 you said the library "works well with one or two or more BNOs", but then you described yaw problems with two BNOs, so one of those statements is incorrect.

I've never heard of an "electronic transformer". Sounds like chinglish. Try outputting a 100mV 50 Hz sinewave from your waveform generator into the "Sec" side of the ET-60-3. That low voltage shouldn't hurt anything. Use your oscilloscope to measure the sinewave on both sides. Does the ET-60-3 step-up the sinewave by about 20 times? If yes, then it's an ordinary transformer with magnetic core and windings. If no, then it could be a switched-mode AC-to-AC converter with a misleading label.

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lumex
 
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Re: BNO085 calibration and performance

Post by lumex »

Hi,

@jps2000
The three images are with rotation vector (0x05). They are 3 sample situations (to answer gammaburst's question about what they are).
2 digits are enough to see measures of i j k changing as with Euler angles.
Moving around Ox changes i and j, same direction.
Moving around Oy changes i and j, opposite directions.
Moving around Oz changes k (as for yaw).
"Status" is growing up to 3 very quickly (seconds) just moving around with BNOs in hands.
This observation gives a bit of intuition about quaternions.

Checking if (normalized) quaternion's norm is 1.0 :

image 1
q1 : 1.00^2 + 0.01^2 + (-0.03)^2 + 0.04^2 = 1.0026
q2 : 0.95^2 + 0.02^2 + (-0.02)^2 + 0.32^2 = 1.0057

image 2
q1 : 0.32^2 + 0.01^2 + (-0.01)^2 + 0.95^2 = 1.0051
q2 : 0.11^2 + 0.02^2 + 0.00^2 + 0.99^2 = 0.9926

image 3
q1 : 0.61^2 + (-0.01)^2 + (-0.00)^2 + 0.79^2 = 0.9963
q2 : 0.47^2 + (-0.01)^2 + (-0.01)^2 + 0.88^2 = 0.9955

Conclusion: quaternions produced but the 2 BNOs have a sound norm.

Hypothesis: as roll and pitch are very satisfactory (great accuracy and reproducibility), it looks like the magnetic field measures are incorrect, especially North measure (hence computed yaw).

Do you agree with that?

@jps2000: "I would also like to see this heading estimation value the BNO is also sending. There should be a possibility to plot this as well."
Do you mean you want to see also yaw on the same screen? (yaw is synonym for heading, afaik). Or do you want to see a graph with plotted values in order to observe jumps/glitches?

I don't need "such a high yaw tracking accuracy". For the time being, yaw is very inaccurate, with poor reproducibility.
I need 2+ BNOs giving the same orientation with a yaw bias of +/- 3 or 5° (maximum). I can accept that yaw is incorrect only if this is the SAME inaccuracy on every BNO (!), i.e. a yaw bias around 3 to 5°, but a yaw bias between 2 BNOs of 20°+ (and "jumping") is not acceptable.

The application is for measuring the relative position (and movement) of two objects possibly mechanically connected more or less loosely (mainly 1, 2 or 3 DOF in rotation + small translations). It's not possible to use a mechanical or optical encoder as in a robot arm, hence I decided to try this absolute orientation sensor.

@gammaburst
Yes, I can also observe jumps with quaternion's measures (yes, jump is "a sudden change by a large amount even though the sensor is moved by only a small amount").
e.g. i_bias jump from 0.00 to 0.40 while just moving like gently water in a bowl then going back to 0.00 .
I can see that i j k are all jumping together.
BUT then I can observe (r_bias, i_bias, j_bias, k_bias) = (-0.05, -0.00, 0.00, 0.02) staying stable.
As with experiments with yaw, I can observe a poor reproducibility with quaternions when doing the same movements I'm now used to do.
(BTW, switching off and on (empty battery) gave then (1, 0) or (1,1) for status. Eight figure loops having no effect on status. Putting the BNO with 0x up, down and the same for Oy and Oz seemed to be a trick. TO BE DISCUSSED).

For that reason and considering the function quaternionToEuler), I think that this function seems not to create that jump.

Do you agree with that?

Minimal example with one BNO085: "Is there any jump in measures?". Let me test that...

I said the library "works well with one or two or more BNOs" : Yes, I meant that starting from nothing I could get measures from 2 BNOs while the library is designed for only one BNO. The trick was to use an I2C mux.
"but then you described yaw problems with two BNOs" : Yes, it's exactly what we are discussing, an accuracy problem with yaw measure.

"The pipe is open": signals/raw data from the sensors are flowing to the arduino program for computation.
Wait a minute...

What I didn't check:
1/ is that I2C pipe sufficient for transmitting the information of 2 BN0s?
I just added a pullup resistor on SDA as suggested by jps2000.
2/ is SPI giving better/other results than I2C ?
PS: I know how to use these two protocols but I'm not an expert in analysis of the I2C or SPI bus of a system.


Regarding the isolation transformer
I'm really not comfortable with this "electronic transformer" (in Chinglish language!!! probably with no coils) and with AC voltage and current measurements until I have a correct multimeter to do that safely.
If I understand correctly these AC measurements, I don't really need an isolation transformer if I have a serious multimeter. Correct ?

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jps2000
 
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Re: BNO085 calibration and performance

Post by jps2000 »

1)You do not need insulation transformer when you have a multimeter with AC current facilities and you keep your hands behind your back when measuring.
2) communication protocols does not matter when it works
3) heading estimation: see sh2 reference manual of BNO085 Chapter 6.5.18.2 The last two bytes are accurracy estimation of heading.
4) to your application: You can always calculate the absolute angle between 2 BNO using quaternions without having a precise abolute position of each BNO. You need however to find a timepoint with a known angle and set an offset as zero.

Below find how to calculate angle between 2 quaternions
//*************************************************************************************
//Angle between quaternions
float dotproduct = Q0 * q0 + Q1 * q1 + Q2 * q2 + Q3 * q3;
float angle = radtodeg * 2.0f * acos(dotproduct);
//*************************************************************************************Jizhong XiaoJizhong Xiao
//**************** dphi calculation************
float argument = (QT0 * Q0 + QT1 * Q1 + QT2 * Q2 + QT3 * Q3); // calculate delta angle to previous sample
if (abs(argument) > 1) argument = 1.0f; // check for N/A

if(asin(argument) > 0) dphi = 2.0f * acos(argument);
else dphi = 2.0f * (PI - acos(argument)); // in case rotation is >360 deg ( quat flip signs)

dphi *= radtodeg; // conversion to deg
if(dphi < 1.4f) dphi = 0.0f; // Noise cancelling (empirical value)
//*********************************************

Could it be that you have not degaussed both BNO? But one can have pos deviation the other a negative. so 5 degrees difference is within spec

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lumex
 
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Re: BNO085 calibration and performance

Post by lumex »

Hi jps2000,

I've just degaussed again the 2 BNOs with the blue degausser:
doing 9 spots on each board according to the discused and understood degaussing procedure.

Test 1: program displaying rool/pitch/yaw.
"status" goes quickly to (3, 3)
First, R bias and P bias are still fine. Y bias is very good and even Y1 is 1° and Y2 is 2° away North that a compass says.
Then, moving around and going back to the same place for measuring again gives an not satisfactory situation:
R and P are still fine BUT Y1 is -5° and Y2 is +10° giving a 15° yaw bias. It can grow up to 25°or even 45°

Test 2: program displaying quaternions.
quick test : satisfactory then some bias appears.

Do you think that the BNOs are degaussed enough?

How can I test that it's degaussed enough?

I think we already discussed about measuring or testing the magnetic field around the BNOs.
There are several ways (as far as I remember or imagine):
- use a hall effect sensor (I’ve bought one, successfully checked, that measures the mag field of a magnet ; I need to test it’s detection treshold for slightly magnetized objects); I imagine moving the sensitive part all around the board
- use a compass (the needle is my friend but will it be sensitive enough?)
- use another magnetometer to detect mag field abnormalities (on a breakout board it's not easy to approach the sensor from the inspected board)


1/ AC current measurement:
Ok. I should get a good multimeter today.

2/ Communication protocols:
Ok, it should just work.

3/ Heading (yaw) estimation:
I can see (6.5.18.2 - sh2 Reference manual) "The units for the accuracy estimate are radians" and in the chart "byte 12 is Accuracy estimate LSB and byte 13 is Accuracy estimate MSB
I can see that it's easily available as a float accuracy in the library
Let's go exploring that...

4/ Application
Thank you for the function dphi. I'll try it out.
I can't calibrate (i.e. "finding a timepoint with a known angle and set an offset as zero"). Each of the two objects that are loosely coupled must manage itself its orientation...
If I can get yaw accuracy of 5° then with the observed excellent roll and pich accuracy, I think it will do the job.

PS: I'm not sure I understand what is "Q point" in the context of SH-2 Reference Manual. Can you explain what it is exactly?

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gammaburst
 
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Re: BNO085 calibration and performance

Post by gammaburst »

Hi lumex,

Your quaternion jump test results suggest that the quaternionToEuler conversion is probably not causing the jumps. (I say "probably" because we should avoid using absolute words such as "never" and "always" when debugging stuff.) Either the BNO or the BNO library is probably causing the jumps, but I don't know which one. I can't seem to reproduce the jumps.

Adafruit says the library wasn't designed with multiple BNOs (or a mux) in mind, so maybe it has an obscure bug that somehow causes jumps when talking to two BNOs. Maybe the jumps will disappear when talking to only one BNO. Maybe.

In February 2021, jps2000 and I discussed using I2C and SPI to talk to multiple BNO085s, and I wrote some experimental speed tests that avoided using the BNO library. (You saw that on July 31.) When I requested data reports faster than the BNO could output them, some reports were lost, but I never saw weird data or corrupted data or jumps. I don't know how much BNO data you need, so I suggest trying I2C first (its easier), and then if it's not fast enough consider SPI.

My test for successful degaussing is to do that orthogonal rotation test (north south east west up down) and confirm the magnetometer reads about the same in every orientation (except for axes swaps/flips), and confirm those readings are similar to the NOAA prediction. In other words, whichever BNO axis points north should correctly read the north component of Earth's field, and so on for each axis.

Remember that nearby ferrous metals, even if they aren't magnetized, can distort Earth's field.

A multimeter with AC current ranges will allow you to easily measure the degausser current, if you are careful near the 240VAC wires.

If that "electronic transformer" is really a switched-mode AC-to-AC converter, then it's a one-way device, so don't apply power to its output pins unless you enjoy smoke/sparks/fire.

Helpful tip, if you use the Arduino IDE:
- Press Ctrl+Shift+M to print your project's serial messages in a text window.
- Press Ctrl+Shift+L to plot your project's serial message data values in a graph window.

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jps2000
 
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Re: BNO085 calibration and performance

Post by jps2000 »

The q point defines the decimal point. That is different depending on the resolution in bit of the raw data in the data stream which is MSB+LSB a 16 bit integer
I use it like this
#define QP(n) (1.0f / (1 << n)) // 1 << n == 2^-n

and here I compute for example heading estimation having QP(12)

h_est = (((int16_t)cargo[22] << 8) | cargo[21] ); // heading accurracy is composed of byte 22 and 21
H_est = h_est * QP(12); // apply Q point this is 12 not 14
H_est *= radtodeg; // convert to degrees

But the bosch library is doing that for you .
This can be programmed differently of course. above is made for 8 bit AVR processors not having divisions
I used the BNO with an ATMEGA 328 using my own not bloated code. (see github)

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lumex
 
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Re: BNO085 calibration and performance

Post by lumex »

Hi gammaburst,

Function quaternionToEuler: ok, should not be the cause.

I2C is enough for the time being: ok. I'll try SPI if more speed is required.

Adafruit library:
I just tested a program for one BNO . After 10 mn playing around with it, I could NOT see any jump in displayed measures.
To avoid using this library, I understand that I need to have a look at jps2000's library or to look at your 2021 speed test.

gammaburst's Degaussing test of a BNO breakout board :
1/ Place the BNO in all orthogonal positions (north south east west up down) and confirm the magnetometer reads about the same in every orientation (except for axes swaps/flips)
2/ Confirm those readings are similar to the NOAA prediction.

I've done a quick test on the corner of a vertical 25 mm thick wooden board put in position with a level bar. One edge of the BNO board is placed to one edge of the wooden board with the accuracy you can imagine (1-3° ?)
On each axis, turning the BNO board 0°/90/180°/270° I could find the expected behavior of swapped/rotated values, BUT with too important bias.

Example : turning the board in 4 orthogonal positions around Oz axis (easy : just turn the board on it's back) gave the following results:
---
degaussing_test_000_red.jpg
degaussing_test_000_red.jpg (209.37 KiB) Viewed 29 times
degaussing_test_090_red.jpg
degaussing_test_090_red.jpg (193.08 KiB) Viewed 29 times
degaussing_test_180_red.jpg
degaussing_test_180_red.jpg (194.5 KiB) Viewed 29 times
(no photo for 270° because of the maximum 3 photos limitation...)
---
0° : Bx = +22.62 uT By = +0.81 uT Bz = -22.69 uT
90° : Bx = -7.56 uT By = -20.69 uT Bz = -26.44 uT
180° : Bx = -32.81 uT By = -3.44 uT Bz = -23.94 uT
270° : Bx = -0.69 uT By = -23.62 uT Bz = -24.25 uT

It's the same with the tests around Ox and Oy.

I'm going to degauss again this BNO board on each side and on the edges...


Thanks for the "Serial plotter" feature. I never used it before. There is a bunch of measures and I can't get the checkbox for selecting what to display like in Arduino IDE 2 Tutorials - Using the Serial Plotter Tool because I'm using v1.8.15 .
One year ago, I heard that arduinoIDE v2 was not very stable. Is it stable now ? Did you try it?

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