I am in the process of rebuilding my distribution panel and trying to clean things up a bit. I have several long I2C runs using Cat6A cable along I2C extenders. All work well but my question is can I use a single extender for multiple I2C connections to the same ESP32.
Using this RJ45 breakout board: [ELECTRONICS-SALON RJ45 8P8C Jack 4-Way Buss Breakout Board, Terminal Block, Connector. ELECTRONICS-SALON D-237, ELECTRONICS-SALON MD-D237-1]
And this I2C extender: [Adafruit LTC4311 I2C Extender / Active Terminator [STEMMA QT / Qwiic] : ID 4756 : Adafruit Industries, Unique & fun DIY electronics and kits]
Can I connect a single extender into the solder pads of the RJ45 breakout board and have it work for all four connections? I do not have an oscilloscope to test it.
I haven’t done this yet myself … but have been looking into it to place some sensors a couple of metres away from the controller in my stand-alone greenhouse.
The Adafruit LTC4311 seems pretty nifty to boost the signals, and one is in my next order to test out … but the real issue is the total length of i2c wiring. I noted that all i2c devices are in parallel on the bus - so it does not matter where the LTC4311 is in the circuit, and got the impression that there would be minimal benefit from multiple LTC4311s. So yes, I also would place it between the ESP32 and breakout board.
I came across a discussion suggesting to use ethernet cable, putting each of the i2c signals down the different pairs with all the earth wires connected to reduce interference for longer cable lengths - which I guess is what you are already doing.
I believe is pretty similar to Sparkfun’s QwiicBus endpoints, which I was thinking of as a backup plan or for longer cables.
Whereas the Sparkfun QwiicBus is intended to create a long chain of i2c devices, the RJ45 breakout board you mention creates a star network. It doesn’t matter which way you go - total cable length is the key factor. If you go with the RJ45 Breakout Board you should consider what signal to connect to which of the 8 screw terminals to ensure they are going down different twisted pairs in the ethernet cable.
I note that some of the newer ESP32 processors allow two i2c busses, so that might be another option.
I would be interested to hear your real world experience.