Anyone use Arduino on layout

Well, that might not be the way I'd solve it, but I was looking for a canned solution.  I figured this would isolate all the leads, including the ground.

I believe you only need one lead, but you do need to isolate the ground as well, so it calls for a separate power supply that is isolated from the one that the rest of the logic runs from.

I suspect if I looked a bit there are pretty cheap single channel opto-isolators for RS-232 as well.

Here's one at a much cheaper price.

http://www.serialcomm.com/seri...ct_general_info.aspx

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!

This is pretty easy, you don't need 20ma for LED's.  For signals, you can easily get by with 10ma or even less.  I think if you try the signals on 20ma and 10ma, you'll see that there is very little difference in the appearance.

With 50 feet of #24 wire and 10ma, the voltage drop for the round trip (100 feet total) would be about .05 volts.  I don't think that's going to be a problem.

I'd tend to use the KISS principle and use just one processor to run this.  Building the communcation between multiple units runs up the complexity for no significant gain that I can see.  If you just want to do it as an intellectual exercise, it might be fun.

You can also put the 74HC595 shift registers around the layout and just run the signals to the, using some modest noise filtering.  We're not doing space shots here, so designing for bulletproof operation isn't as critical as some.  I've run digital signals 100's of feet on a current loop and never run into any issues.  I build digital keypads for video display systems with a 20ma current loop and I ran the wires many hundreds of feet back to the controller.  There was never an issue with reliable operation.

Drive each load with an emitter follower.