hi, what would you estimate or know is the maximum useful length of cables for an I2C connection between the Arduino and the I2C thing? Provided that + and GND are available and i only have to extend the SDA and SCL cables?

Keep in mind that the I2C standard was designed for communications between ICs on the same board or at best between boards in the same system via backplane connections. There are I2C buss drivers that can effectively increase the length and using quality twisted pair shield cabling can help, but you…

That was my concearn - that I2C was 'just' made for component communication... In the end i would like to drive a few Port expanders via I2C and the data that is send consists of just a few byte (I2C Adress and Port settings) every few seconds.... And the length would be possibly up to 30, maybe 4…

What speed do you require? You may be able to run longer distances at slower speed. IIRC the I2C spec lists performance data for loads up to 400pF. Take a look at the capacitance per foot of your cable and see how close you are. IIRC TI makes repeaters with higher current drive. For 30 - 40m you …

hm, ok. thank you... The idea of having uCs at both ends is interestering.. would offer some more stuff that's be possible.. hmm... Well.. have to see what i may do about it.. it's yet still just some sort of mind experiment to determine if it is doable at all..

I2C - maximum cable length?

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I2C - maximum cable length?

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