i2c pull-up resistors, and chaining PicoBorg Reverse with other devices

Submitted by lars_the_bear on Tue, 02/02/2016 - 09:37

Forums:

Hi

I'm trying to work out whether the PB Reverse, and platforms that employ it, are suitable for my project.

My understanding is that multiple i2c devices can be connected in parallel to the same GPIO pins, but there should only be one pull-up resistor to +3.3V. I understand that there is a little flexibility in what value of pull-up to use, but values of 3k3 to 10k seem to be common.

So -- does the PB Reverse have internal pull-up resistors? If so, what values are they? Can they be removed if necessary?

Best wishes
Kevin

piborg's picture

piborg

Tue, 02/02/2016 - 13:03

The PicoBorg Reverse does not have any pull-up resistors fitted for the I2C.
The reason for this is that the Raspberry Pi provides the pull-up resistors for the I2C line itself.

I believe the Raspberry Pi has 1.8 KΩ pull-up resistors to the 3.3 V line.
As far as I am aware these can be removed if you needed to, but I do not know which ones they are on the board or how easy they would be to remove.

lars_the_bear

Tue, 02/02/2016 - 14:32

Hi

OK, thanks. Given the presence of on-board pull-ups, I'm not sure why some i2c-based devices have their own pull-ups.

This thing:

https://learn.adafruit.com/assets/1857

seems to pull up to 5V, if I am reading their documentation correctly. This seems a bit dodgy on 3.3v pins, but maybe I'm missing something.

Oh, well, not your problem.

Best wishes
Kevin

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