I2C Slave with a PIC

[pedja089]

SDA and SCL are not good combination in one pair. Because of cross talk.
Much better is to combine GND and SDA on ona pair, GND and SCL on second pair. But capacitance play big roll. Probably CLK must be driven, not with pull up. SDA should have strong pull up.
But do not connect multiple GND on both sides, as that will create long loop antenna, probably...
I thing, but maybe i'm wrong, best chanse to get it to work is:
1. Pair GND and signal on 2 pairs for SDA and SCL, connect that ground only on output port of module.
2. Use third pair for power
3. Ground unused pair master, as GND for signals.
Generally not good idea to run TTL signals out of boards.
If you design master and slave's why not to go with RS485, half duplex or duplex?

[richard]

Personally, I start getting nervous as soon as a signal leaves a board!

me too

spi can get that sort of distance but you need a cs signal for each slave

I wonder if you used a pair of those 3v-5v level shifters back to back if they could act like a repeater ?
could be a cheap solution

wireless may be an option
rfm69 modules and the like can get 300k bps over that range and a master slave setup is no too difficult