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I2C pullups
Moderators: adafruit_support_bill, adafruit

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I2C pullups

by GardenGeek on Sat Nov 27, 2021 9:35 am

So, I am relatively new to AVR programming and electronics, and I am learning a lot as I go. One thing that I have not figured out yet is that I have noticed the other day that all of my I2C sensors have some sort of pullup on them. Some ar 4k7, some 10k. I have also realized that my controller, a Metro M4 Airlift Lite, also has pullups according to the specifications. Everything seems to be working correctly even though I have not cut any traces to the resistors. Having only a couple of sensors, what problems might this cause, and should I see about cutting out any resistors? I have been running a test of my project over the last several days without any issues.

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Re: I2C pullups

by adafruit_support_bill on Sat Nov 27, 2021 10:03 am

In most applications, the exact pullup resistance is not that critical. Since many processors do not have pullups on the i2c lines, we put 10K pullups on nearly all of or i2c boards.

In most cases, you can have at least 3 or 4 of these devices on the bus before the combined pullup strength becomes too much for the processor. If you do start to have i2c communication problems, try removing a device from the bus. If the problem goes away, it is likely a pullup issue. Removing the pullups from one or more devices should solve it.

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Please be positive and constructive with your questions and comments.