# I2C question about pullup resistors

**URL:** <https://discuss.blues.com/t/i2c-question-about-pullup-resistors/217>\
**Category:** Hardware\
**Created:** [April 24, 2021, 12:30pm UTC](https://discuss.blues.com/t/i2c-question-about-pullup-resistors/217 "2021-04-24T12:30:21Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Pat](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/pat/32/143_2.png) [@Pat](https://discuss.blues.com/u/Pat)\
**Post date:** [April 24, 2021, 12:30pm UTC](https://discuss.blues.com/t/i2c-question-about-pullup-resistors/217/1 "2021-04-24T12:30:21Z")

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Are there pullup resistors on the Notecard I2C lines already? Or do they need to be added externally?

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**Author:** ![bsatrom](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/bsatrom/32/3_2.png) [@bsatrom](https://discuss.blues.com/u/bsatrom)\
**Post date:** [April 25, 2021, 3:18pm UTC](https://discuss.blues.com/t/i2c-question-about-pullup-resistors/217/2 "2021-04-25T15:18:06Z")

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Hey Pat, good question. There are pullups on the SDA/SCL lines of the Notecard, so you should be ok at the prototype phase using the pullups already on the board. If you’re looking to spin your own board for a pilot or deployment, we suggest putting a scope on the SDA and SCL lines of your design just to make sure the signals perform as you expect, and add additional pullups, as needed.

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**Author:** ![electrobirdy](https://avatars.discourse-cdn.com/v4/letter/e/f6c823/32.png) [@electrobirdy](https://discuss.blues.com/u/electrobirdy)\
**Post date:** [October 26, 2021, 11:06am UTC](https://discuss.blues.com/t/i2c-question-about-pullup-resistors/217/3 "2021-10-26T11:06:39Z")

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Hey, quick followup question: in the **Notecarrier-AE schematic v1.7.pdf** I couldn’t find any hardware pullups on these lines, I could only find the 100 ohm series resistors. Are they internal pullups and do you happen to know the resistance values?

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**Author:** ![gwolff](https://avatars.discourse-cdn.com/v4/letter/g/a88e57/32.png) [@gwolff](https://discuss.blues.com/u/gwolff)\
**Post date:** [October 26, 2021, 12:39pm UTC](https://discuss.blues.com/t/i2c-question-about-pullup-resistors/217/4 "2021-10-26T12:39:46Z")

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Thanks for posting. That’s a great question.

Yes. There are internal pull-ups. They are 10 kOhm.