Looking ahead a bit, I envision a bunch of Arduino based controllers placed all over the layout. A full fledged ABS or CTC signaling system could amount to a microprocessor at each block. Add to that controllers for grade crossings and servo controlled switch machines and there could be more than you would want to disassemble for new software upgrades.
What is needed is a way to communicate between the various microprocessors. The good news is that there is hardware that makes this fairly simple; RS485 multi-drop connections. The bad news is that, while I've tried to work out something on this, I have not had much success.
Still, if the Signal Controllers were connected as addressable units, the chaining of signals for block control could be achieved with messages sent one to another. Software upgrades could also be done using the same communication link so that all units of a certain type could be downloaded at the same time and without being extracted from under the benchwork. RS485 is two wires, usually in twisted pairs.
