Electronic – arduino – Reduce noise on 2m I2C bus using motorcycle power

When using I2C you must remember to put a pull-up resistor (something like 3.3kohm or 4.7kohm will work) from each line to power. I2C has the ability to communicate to multiple devices on each line using device addresses, so you will have to check what the device address of the xbee is in it's data sheet. Here is the I2C reference page for Arduino which will come in handy:

http://arduino.cc/en/reference/wire

Edit:

I just recalled that Xbee does not support I2C directly, but instead uses UART for communication. Simply use the Tx and Rx pins on both your Arduino and Xbee. No pullups are required for UART. Here is the UART arduino page: http://arduino.cc/en/reference/serial

IIC is going to be problematic. You are sending a clock signal out to the remote devices and that clock signal (when it arrives) clocks back data to the master and the master reads the data by clocking it back in but the clock the master is now using bears little resemblance to the delayed clock at the sensor and the data coming back is delayed even more. This has to mean running as slow as you can get away with.

Given that you have interference issues I'd suggest running clock and data down coaxial cables - at least try it to see if it helps - it won't help the data be more aligned to the clock at the master but it might stop interference giving you a hard time.

I had to send SPI bus to a remote device at 10m - data was being sent from the master only so both clock and data were properly aligned (cable length same distance) - I was using 2MHz clock but I decided that the only way it would work reliably was with differential drivers and receivers on both clock and data. It worked of course and I might have got away with coax but I'm sure regular unshielded cable and single-ended data and clock wouldn't work reliably.