On my device there are two boards with 10 kOhm resistors between i2c and 5V. This is SparkFun level shift and LCD screen. Do I need to have a pull-up in the chain in only one device?

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closed as unclear what you're asking by Chris Stratton, pipe, RoyC, Elliot Alderson, Dmitry Grigoryev Jan 15 at 14:47

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    \$\begingroup\$ It's not clear exactly what your situation is or what you are asking, but generally a 10K pullup is weaker than recommended for I2C. If you have multiple pullups on the same segment (the same side of the level shifter) their effect would combine. Two 10K pullups in parallel would actually fall just short o the the recommended I2C territory of < 4.7K ohm. 2.2K (net effective) is more typical. \$\endgroup\$ – Chris Stratton Jan 5 at 6:32
  • \$\begingroup\$ Алекс - As Chris has said, unfortunately your design is unclear - e.g. you say that you have "two boards" but does that include the Sparkfun level shift[er] (level translator), or are there two boards in addition to that? It's also unclear how the LCD display is connected e.g. is it on the HV or LV side of the level translator, and does it have any pull-ups of its own? I suggest that you edit the question, add photos of your actual boards, and add a diagram (either drawn in the built-in schematic editor, or a clear hand-drawn one) of the intended schematic. What I2C speed are you using? \$\endgroup\$ – SamGibson Jan 5 at 14:35

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