I had considered using the Arduino Nano as a base for the control function. It has lots of I/O pins and is dirt cheap. The external circuits would be for input and output signal conditioning and of course a generic source of power. While you could consider a DC power brick for the power, I think having a bunch of little bricks, one for each unit, may be a bit cumbersome, so I was thinking along the lines of an AC power supply that will work from track power or accessory power from around 12 VAC to 22 VAC.
Some of this is getting a little "over the top" for a cheap signal. Also, all of those intricate signalling variations have to be accommodated by the logic. If this starts out so complex that it's a six month development project, it's probably dead already. 
Also, if we start with the hardware base to support some of this stuff, the software can be customized in the future to expand the capability of the signal board.
CGWforever posted:What about two light block signals? I see this show three lights.
You simply don't connect to one of the outputs. Connect to the red and green only, presto, you have a 2-light signal.
