Okay, new question for my electrical genius friends . I had planned on controlling all of my signals (LEDs) directly driven with a series of daisy-chained 74HC595 shift registers. But I saw some cautions regarding the amount of current that the 74HC595 could handle on the outputs -- 20ma per pin, but 70ma total for each chip -- so you can't draw 20ma from all 8 pins at the same time.
With a signal system, I would be illuminating up to 4 of the 8 pins at any one time (either Red or Green, for each of 4 dwarf signals for example.)
Given the above, and the fact that my layout might require that a signal be as far as 50 feet away from my main control area -- can you even drive LEDs from 50 feet away? And if so, will the 74HC595 provide enough current? What value of resistors should I use (I will likely use Z-stuff 2-aspect dwarf signals, if that is relevant)?
Two other options that come to mind would be to use TPIC6C595's, which I *think* are identical to a 74HC595 except that can provide a lot more current (though the data sheet does not use the word "latching." Or, since even Arduino Megas are only $15 each on eBay -- I could place a few Megas in strategic locations around the layout, and let them drive the LEDs directly from their digital I/O pins.
In the second scenario (multiple Arduinos) my concern would be what communication bus should I use -- as I understand that I2C (which I had planned on using between my various dedicated Arduinos) is only good for about one meter or so in length. Similar for SPI.
I suppose RS485 is an option (I need to link several Arduinos) but still would need to understand just how far I can run LEDs from even a "local" Arduino's I/O pins...
Thanks as always for your thoughts!