I have a working i2c line pullups setup for my i2c gpio expander chip on a breadboard.
What I am aiming for now is an official pullup setup for my circuit, without a breadboard.
I am having a hard time finding out if that board has any internal pullups to just directly connect cables to i2c ports, or are there any other external pullup quick minimal workarounds? As during this time, ordering a designed PCB is the very very last and least favorable option for me.
You can enable the internal pull-up resistors in the MCU, however the value is around 40k ohm’s and may not be enough to operate i2c reliably at higher frequencies and longer device wiring distances.
Here’s a recent post with some further information.
I recommend external 10k resistors for a pullup, this has the advantage that it is independent of the MCU, even when it is in deep sleep or suspend mode. When you have long cables between the I2C device and the MCU lower values are required to get stable signals, e.g. down to 1k for 2 meter cables. For longer cables (>15cm) check the signals via a scope and than decide the pull-ups.