I2C bus length between 2 Arduinos

I'm wondering what sort of experience others out there have had with connecting 2 boards over I2C. I've done a few searches and everything is kind of vague. I'm interested in understanding the "standard" possibilities for 2 boards running at 16Mhz without an extender, and just a couple simple pull up resistors on the master.

Here's my experience: I thought telephone wire would be a nice choice: 4 conductors, easy to find, modular connectors, cheap, etc. At about 12' the boards would sometimes communicate, for a little while before loosing sync. At about 8' it seems to be pretty reliable.

Other conductors? Would shielded microphone cable work better and if so how much?

Did you follow the guide lines on cross talk for cabling for I2c ?.

Use Twisted cable and twist SCL and SDA with Gnd or Power ?
Don`t twist SCL / SDA together .

"Did you follow the guide lines on cross talk for cabling for I2c ?." - LOL, of course not! I just grabbed some wire and tried it!

Peter - Thanks for the "twisted" advice. I wasn't sure what the strategy for that would be. So I take it that twisting both SCL and SDA with Gnd would be a good arangement. I'll try to read up on those guidelines (where ever they are) I thought about using some Cat5 cable, but the stuff I have has solid core wire so I didn't bother (I need flexibility). What kind of run could be expected with Cat5 hooked up that way? Do you have any numbers?

So I take it that twisting both SCL and SDA with Gnd would be a good arangement.

This would be a bad arrangement according to peter247’s post. SCL and SDA should not be twisted together at all. Twist one with power and the other with ground

Thanks DaruDude I understood that they shouldn't be twisted together, but I had the impression that each line being twisted with a ground wire (separate ground wires for each) would be OK. So if I understand things fully (doubtful) SDA can be twisted with Vcc or Gnd and SCL gets the opposite one (Vcc or Gnd)

http://www.scribd.com/doc/4569852/The-I2C-Bus-Specifications http://www.i2cchip.com/i2c_connector.html