RAK3172 RUI3 I2C mulfunction

I am trying to attach I2C sensors to the RAK3172 module. Actually I am using the RAK3272S board but in my case i guess it doesn’t matter.
I use the RUI3 framework v3.4.2. I’ve flashed the sensor node example without any modifications and took a look with an oscilloscope at the I2C pins. The datagram is really odd. I looks like the I2C pins are configured in ‘slow mode’ and they are not changing their state quick enough. Especially the CLK pin
As a consequence none of the I2C sensors I have work.

Can you give me any hint how to configure I2C to operate correctly?

Thank you

Update: I’ve tried to witch I2C from 400kHz mode to 100kHz mode. The behavior of the signal remains the same:

Welcome to RAK forum @aho ,

This is a strange problem. Maybe you can double check the I2C bus wiring? Like the value of pullup resistor, if there possible extra unnecessary connections, etc. Also for sanity check, maybe you can try to connect a different I2C device than the one you currently use?

Hi @carlrowan and thank you)
The datagram is taken from the module without any connected devices. There are literally only power pins connected to the 3272S board.
Do I need to use external pullup resistors? I remeber I saw somewhere in the documentation that for 3172 I2C pullups are not needed. But now I was not able to quicly find the proof link, sorry :slight_smile:
I have a couple of raw 3172 modules. I can try to unsolder the one on 3272 and replace with another 3172 module I have if it looks like a hardware module issue

Maybe this is on the RAK3172 Evaluation Board documentation?

The RAK3272 (RAK3172 in breakout board) doesn’t have an pullup resistors so it is still needed :+1:

Ok, updating the thread
With 1K pull-up resistors I get rise time of ~150ns. The I2C sensor seems to like it and works ok.
With 4K7 pullups the rise time is ~500ns and the sensors do not work

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Good thing to know it works somehow. But 1k seems low as a pullup. What is the sensor? Do you think there is some kind of parasitic capacitance in your setup that causes the slower rise time? On our WisBlock Base boards, we only use 4.7k and got no issue communicating with the modules.

The diagram and rise time measurements are taken without connected sensors. So it’s only the Rak3272S in the circuit.
@carlrowan can you get the oscilloscope diagram from hardware guys please? For the reference.

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