Wanting to control a split flap display that was not near a computer [Tom] looked to a common solution for communicating over distances not practical for I2C or SPI. He developed his own hardware and packet format using the RS-485 protocol.
This is part of a larger project he has been working on to feed data to a split flap display that he plans to hang on the wall. RS-485 is designed to work over long distances and overcome noise issues. The core of the communications system is the board seen on the left. It uses a MAX1483 chip, a pair of RJ45 jacks for Ethernet cables, and two terminal blocks for power and communications. There are a few nice things about this. The board acts as a pass-through making it easy to chain nodes together, and the data structure is completely independent of the hardware itself. Because of this [Tom] developed his own packet format that will be a bit more resilient than the Arduino networking scheme we looked at the other day.