Pull up resistors for I2C

Hello everyone, I am an electronics noob so please have mercy (=

I am planning on making my own little breakout board with a couple of EEPROM chips and I want to use I2C to connect it to my Arduino. While planning the board I remembered that I2C is open drain which - as far as I understand it - means that SDA and SCL need to be connected to 5V through pull-up resistors.

Here is my problem/question: when I want to use my own breakout board as the only slave device on the I2C bus I need to build in some pull up resistors and connect the SDA and SCL line to 5V on the board through them. But what if I want to have more slave devices on the bus? Should they all pull the lines high? Wouldn't that be a parallel circuit which in turn would mean that the overall resistance would decrease and more current would go through the lines?

As far as I know I2C break out boards often implement the pulling up of the two data lines. Can I just use multiple on the same bus regardless?

My question boils down to this: When designing my board, do I need to implement the pull-up resistors for a) "only mode" (only slave device on the bus) b) with multiple slave devices on the bus which as far as I know already implement this.

Thank you for your help in advance (=

It is one pull-up resistor per signal line.

My question boils down to this: When designing my board, do I need to implement the pull-up resistors for a) "only mode" (only slave device on the bus) b) with multiple slave devices on the bus which as far as I know already implement this.

Implement your board with pull-ups but populate them only on one board. Commercial boards often include the pull-ups because the most newbies use just one board and that way it works out of the box. Those people that attach multiple boards often know the basics and desolder the pull-ups on the additional boards.

pylon: Implement your board with pull-ups but populate them only on one board. Commercial boards often include the pull-ups because the most newbies use just one board and that way it works out of the box. Those people that attach multiple boards often know the basics and desolder the pull-ups on the additional boards.

Perfekt answer! Thanks a bunch. Have a great day (=