Wiring for I2C communication between multiple arduinos

Hi folks.

For a project I have to use 3 or 4 arduino that will communicate using the i2c protocol.

But there is discordant information about the wiring.

One say that you can directly connect all devices on the bus without resistor: http://marcoramilli.blogspot.ch/2011/10/communication-between-multiple-arduino.html

Others say that I have to use a pull-up resistor for the bus wires: http://hacknmod.com/hack/how-to-connect-multiple-arduino-microcontrollers-using-i2c/

As I don't have time to make multiple tests, I ask you which one is the correct way of doing it ?

Thanks for your time

Fabien

AFAIK, the correct way is to use a resistor. 10K should be ok.

That's what I thought.

Thanks Tim!

You can also lower the resistor value to account for higher distributed capacitance of the connected devices or an increase in buss signaling rate. A value of 1K is still safe for the occasions where it's needed.