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I2C Pull-up resistors

Pixy Hardware
#1

Hi,
I just received my Pixy and noticed, that there are 10k pull-up resistors from SDA/SCL to +5V (btw. the wiki is wrong here, it says 4.7k: http://www.cmucam.org/projects/cmucam5/wiki/Hooking_up_Pixy_to_a_Microcontroller_like_an_Arduino).

Usually the pull-up resistors are already located at the master side of the bus. As I use 1.8k pull-up resistors in my setup, with the 10k resistors in parallel, this makes a total resistance of ~1.5k. I read somewhere (I2C specification?), that the maximum current draw when the lines are pulled low is 3mA. With my setup the current draw would be I=U/R=5V/1.5k=3.3mA. For now I replaced the pull-up resistors in my setup with 2.2k, which makes in total 1.8k again, everything works fine.

But I’m just intersted: are these pull-up resistors really necessary? Could I (theoretically :wink: ) unsolder them?

Thanks for your answers.

#2

The pullups are there for “extra pull-up assurance”. They don’t do much, but will result in a working system if you leave pullups out of your implementation. They are not the recommended values, for sure. Feel free to desolder, but again, they are inconsequential if you have your own pullups.

thanks!