Originally Posted by skidad68
You can have the Driver Station talk to the roboRIO, and then have the roboRIO talk to the Arduino using the serial port or I2C.
I would definitely recommended this - WPIs I2C wrapper is well documented, as is the Wire library for arduino. The approach I have taken before is to manually enable bits in a single byte to represent certain states like the current mode or alliance, as well as any custom flags I had set like if certain buttons were pressed on a joystick, and then simply sent that byte of data over the I2C bus and had the arduino read that data and process it in a similar way. I have an example of this on github if you would like to see this in practice.