conecting some arduinos

First, sorry for my english. :cold_sweat:
I hope some of you can help me guys- I have one model train layout and I need a way to control the trains. I think this is posible, using one Arduino pro mini in every train and I can use my Due to only send comands to the minis'. The only problem is that I have conection with only two rails an nothing more thats becouse i cant use I2C because also i need the rails for the 12V power for the trains.
My idea is to use 15V betleen the rails for HIGH an 12V for LOW, but i need some kind of protocol or sth to transfer the data and a way to make it not 0V/3.3V but 12V/15.3V.
I hope you have understood my idea and have some ideas for its realisation. :slight_smile:

One way is to use serial data but modulated into tones. With one tone for a logic one and another for a logic zero, like the old fashioned modems.then you can couple this signal to your train track with capacitors at both ends. This means the DC voltage does not affect the signaling.