Getting I2C to work with two devices (one with internal, one with external pull-up resistor)

[robertrondo]

Hi,

i have an Arduino Portenta H7 Lite connected two Xsens MTi-3 IMU's to it. One of the MTi-3's is placed on a Development Kit, which has integrated 2k7 pull-up resistors for I2C communication. The other MTi-3 is placed on a PLCC28 socket adapter and i added the 2k7 resistors manually. The Arduino and the two MTi-3 are connected via breadboard as shown in the following picture (i hope it is clear enough, otherwise sorry i am new to the field of arduino etc.). The yellow lines show the 2k7 resistors.

Now when i first tested the MTi-3 with the Development Kit alone it was working fine (the other was not connected). Also when testing only the MTi-3 on the socket adapter (also the other MTi-3 was not connected to the arduino) it was working fine. But my problem is, when i connect both of them as shown in the picture above, the arduino can't find any I2C slave. I discovered, that when i unplug the 3V3 wire of the socket adapter, i can find the MTi-3 on the DevKit. As soon as i plug in the 3V3 wire of the MTi-3 with extern pull-up resistors again, i can't find any of the two IMU's. I thought maybe it is enough if the DevKit has the resistors and they are connected on the same line on the breadboard. But if i don't use the external 2k7 resistors, the two IMU's also can't be found. Is it impossible to communicate via I2C with two devices, one with and one without internal pull-up resistors? Or what do i need to change?

This may be a small problem, but i searched the internet and couldn't find such a problem or the solution. So thanks in advance and best regards!

Edit: I ensured that the two devices have a different address. And it worked for both of them with each their own address. So i guess the problem is in the setup/wiring.

[ZX80]

Do they have the same I2C address ?

[robertrondo]

No i made sure they have a different address (see my edit )

[ZX80]

Two pairs of pullup resistors should not be necessary.
I know it is not an ideal solution; but you could try with one connected to SPI or serial.

[robertrondo]

Also had this idea but sadly my SPI and Serial are already used.

Is my wiring (parallel connection of SDA & SCL) correct? If i connect them parallel, for my understanding the pull-up resistors of the DevKit should also effect my other IMU, am i right?

[Idahowalker]

Wire them in parellel and get rid of the external pullups and use the internal pull up of the device for both.

[robertrondo]

I just tried that, it doesn't work

But when i unplug the 3V3 of the MTi-3 w/o internal, the other can be found. So the one without internal is crashing the I2C communication, i have absolute no idea why.

I just discovered, that when i run my detection script for a longer time and not just a few seconds, the one with internal pullups gets detected every once in a while. Very strange. Seems like a little traffic jam on the bus.

[Idahowalker]

I2C scanner

I2CScanner - Arduino Reference

Arduino | How to Scan and Detect I2C Addresses | Adafruit Learning System

What did the I2C scanner report?

[robertrondo]

Most of the time it says "No I2C devices found". Randomly and not very often, the one with internal pullups gets detected.

[Idahowalker]

post an image of your project wired up with both devices.

[robertrondo]

i hope the wiring is halfway seeable, it looks chaotic. But the wiring is as in my picture above, just with the difference, that i don't use the resistors.

[Idahowalker]

You know about this and you have adjusted you breadboard accordingly. The wiring images are not all that good at showing much details.

Bread board power rail split

[robertrondo]

i tried to take better pictures. For my breadboard the power rail is continous

[robertrondo]

I will check if there is any damage at the wiring.

One more information: Yesterday i discovered one weird thing. When fully wired (both devices connected) the I2C scanner detects/not detects the MTi-3 on the DevKit in a regularity. First it started and didn't detect any device for a while (about 1 minute or so). Then the scanner detected the MTi on the DevKit once. Afterwards he didn't detect it 5 times. After that he detected the DevKit again. Then he didn't detect it two times. This cycle then repeats mostly constant. The cycle: detect, 5 times no detect, detect, 2 times no detect. For my interpretation it seems like there maybe is an internal buffer or capacity that leads to this behaviour.

[robertrondo]

After measuring electrical continuity i now face a new behaviour:

The I2C scanner detects both devices, but also not everytime. And again we have some kind of regularity. Here is a snippet of the output of the I2C scanner:

12:49:24.513 -> Scanning ...
12:49:30.088 -> No I2C devices found
12:49:30.088 ->
12:49:35.067 -> Scanning ...
12:49:38.822 -> No I2C devices found
12:49:38.822 ->
12:49:43.799 -> Scanning ...
12:49:49.391 -> No I2C devices found
12:49:49.391 ->
12:49:54.390 -> Scanning ...
12:49:59.953 -> No I2C devices found
12:49:59.953 ->
12:50:04.945 -> Scanning ...
12:50:07.560 -> I2C device found at address 0x6A !
12:50:07.560 -> I2C device found at address 0x6B !
12:50:08.074 -> done
12:50:08.074 ->
12:50:13.039 -> Scanning ...
12:50:18.620 -> No I2C devices found
12:50:18.620 ->
12:50:23.641 -> Scanning ...
12:50:29.178 -> No I2C devices found
12:50:29.178 ->
12:50:34.181 -> Scanning ...
12:50:36.827 -> I2C device found at address 0x6A !
12:50:36.827 -> I2C device found at address 0x6B !
12:50:37.294 -> done
12:50:37.294 ->
12:50:42.313 -> Scanning ...
12:50:47.858 -> No I2C devices found
12:50:47.858 ->
12:50:52.871 -> Scanning ...
12:50:58.406 -> No I2C devices found
12:50:58.406 ->
12:51:03.436 -> Scanning ...
12:51:08.978 -> No I2C devices found
12:51:08.978 ->
12:51:13.968 -> Scanning ...
12:51:17.978 -> No I2C devices found
12:51:17.978 ->
12:51:22.965 -> Scanning ...
12:51:28.511 -> No I2C devices found
12:51:28.511 ->
12:51:33.492 -> Scanning ...
12:51:39.050 -> No I2C devices found
12:51:39.050 ->
12:51:44.083 -> Scanning ...
12:51:46.722 -> I2C device found at address 0x6A !
12:51:46.722 -> I2C device found at address 0x6B !
12:51:47.235 -> done
12:51:47.235 ->
12:51:52.206 -> Scanning ...
12:51:57.786 -> No I2C devices found
12:51:57.786 ->
12:52:02.766 -> Scanning ...
12:52:08.334 -> No I2C devices found
12:52:08.334 ->
12:52:13.316 -> Scanning ...
12:52:16.014 -> I2C device found at address 0x6A !
12:52:16.014 -> I2C device found at address 0x6B !
12:52:16.482 -> done
12:52:16.482 ->
12:52:21.470 -> Scanning ...
12:52:27.052 -> No I2C devices found
12:52:27.052 ->
12:52:32.026 -> Scanning ...
12:52:37.570 -> No I2C devices found
12:52:37.570 ->
12:52:42.602 -> Scanning ...
12:52:48.146 -> No I2C devices found
12:52:48.146 ->
12:52:53.167 -> Scanning ...
12:52:57.122 -> No I2C devices found
12:52:57.122 ->
12:53:02.136 -> Scanning ...
12:53:07.682 -> No I2C devices found
12:53:07.682 ->
12:53:12.664 -> Scanning ...
12:53:18.253 -> No I2C devices found
12:53:18.253 ->
12:53:23.224 -> Scanning ...
12:53:25.878 -> I2C device found at address 0x6A !
12:53:25.878 -> I2C device found at address 0x6B !
12:53:26.344 -> done
12:53:26.344 ->
12:53:31.355 -> Scanning ...
12:53:36.915 -> No I2C devices found
12:53:36.915 ->
12:53:41.937 -> Scanning ...
12:53:47.470 -> No I2C devices found
12:53:47.470 ->
12:53:52.483 -> Scanning ...
12:53:58.057 -> No I2C devices found
12:53:58.057 ->
12:54:03.041 -> Scanning ...
12:54:07.143 -> No I2C devices found
12:54:07.143 ->
12:54:12.128 -> Scanning ...
12:54:17.670 -> No I2C devices found
12:54:17.670 ->
12:54:22.687 -> Scanning ...
12:54:28.229 -> No I2C devices found
12:54:28.229 ->
12:54:33.261 -> Scanning ...
12:54:35.871 -> I2C device found at address 0x6A !
12:54:35.871 -> I2C device found at address 0x6B !
12:54:36.386 -> done
12:54:36.386 ->
12:54:41.357 -> Scanning ...
12:54:46.910 -> No I2C devices found
12:54:46.910 ->
12:54:51.927 -> Scanning ...
12:54:57.468 -> No I2C devices found
12:54:57.468 ->
12:55:02.476 -> Scanning ...
12:55:08.026 -> No I2C devices found
12:55:08.026 ->
12:55:13.067 -> Scanning ...
12:55:17.128 -> No I2C devices found
12:55:17.128 ->
12:55:22.116 -> Scanning ...
12:55:27.707 -> No I2C devices found
12:55:27.707 ->
12:55:32.696 -> Scanning ...
12:55:38.271 -> No I2C devices found
12:55:38.271 ->
12:55:43.258 -> Scanning ...
12:55:45.917 -> I2C device found at address 0x6A !
12:55:45.917 -> I2C device found at address 0x6B !
12:55:46.383 -> done
12:55:46.383 ->
12:55:51.363 -> Scanning ...
12:55:56.920 -> No I2C devices found
12:55:56.920 ->
12:56:01.949 -> Scanning ...
12:56:07.484 -> No I2C devices found
12:56:07.484 ->
12:56:12.473 -> Scanning ...
12:56:15.163 -> I2C device found at address 0x6A !
12:56:15.163 -> I2C device found at address 0x6B !
12:56:15.630 -> done
12:56:15.630 ->
12:56:20.642 -> Scanning ...
12:56:26.192 -> No I2C devices found
12:56:26.192 ->
12:56:31.180 -> Scanning ...
12:56:36.726 -> No I2C devices found
12:56:36.726 ->
12:56:41.737 -> Scanning ...
12:56:47.279 -> No I2C devices found
12:56:47.279 ->
12:56:52.320 -> Scanning ...
12:56:56.283 -> No I2C devices found
12:56:56.283 ->
12:57:01.274 -> Scanning ...
12:57:06.857 -> No I2C devices found
12:57:06.857 ->
12:57:11.842 -> Scanning ...
12:57:17.382 -> No I2C devices found
12:57:17.382 ->
12:57:22.370 -> Scanning ...
12:57:25.024 -> I2C device found at address 0x6A !
12:57:25.024 -> I2C device found at address 0x6B !
12:57:25.535 -> done
12:57:25.535 ->
12:57:30.515 -> Scanning ...
12:57:36.062 -> No I2C devices found
12:57:36.062 ->
12:57:41.081 -> Scanning ...
12:57:46.616 -> No I2C devices found
12:57:46.616 ->
12:57:51.646 -> Scanning ...
12:57:54.297 -> I2C device found at address 0x6A !
12:57:54.297 -> I2C device found at address 0x6B !
12:57:54.762 -> done
12:57:54.762 ->
12:57:59.787 -> Scanning ...
12:58:05.319 -> No I2C devices found
12:58:05.319 ->
12:58:10.302 -> Scanning ...
12:58:15.888 -> No I2C devices found
12:58:15.888 ->
12:58:20.876 -> Scanning ...
12:58:26.421 -> No I2C devices found
12:58:26.421 ->
12:58:31.455 -> Scanning ...
12:58:35.545 -> No I2C devices found
12:58:35.545 ->
12:58:40.520 -> Scanning ...
12:58:46.104 -> No I2C devices found
12:58:46.104 ->
12:58:51.107 -> Scanning ...
12:58:56.655 -> No I2C devices found
12:58:56.655 ->
12:59:01.647 -> Scanning ...
12:59:04.299 -> I2C device found at address 0x6A !
12:59:04.299 -> I2C device found at address 0x6B !
12:59:04.767 -> done
12:59:04.767 ->
12:59:09.765 -> Scanning ...
12:59:15.354 -> No I2C devices found
12:59:15.354 ->
12:59:20.350 -> Scanning ...
12:59:25.870 -> No I2C devices found
12:59:25.870 ->
12:59:30.906 -> Scanning ...
12:59:33.520 -> I2C device found at address 0x6A !
12:59:33.520 -> I2C device found at address 0x6B !
12:59:34.034 -> done

[robertrondo]

New update for behaviour:
When only MTi-3 on DK connected the scanner detects him every time.
When only MTi-3 on plcc-socket connected with external pull-up resistors after a short time the scanner detects him most of the time in the cycle: detect, 6x no detect, detect 2x no detect
When both connected after a short time the scanner detects them both most of the time in the cycle: detect, 6x no detect, detect 2x no detect

So in conclusion, as long as the MTi-3 on the socket is connected, there is a irregularity in detecting the device(s). But because when both connected, there is also suddenly irregularity for the MTi-3 on the DevKit, it seems to me wiring is defenitely correct and the problem lies within the communication process itself. But i have absoulte no idea why. Because it is now kind of a new problem, i will open a new thread where i will describe this problem.