I ran into a problem while testing my Arduino system on the layout, so I thought I would update everyone on what happened and what I did to fix it. I would welcome any thoughts people have about the situation.
After I connected a few of the Atlas switches to the relay outputs, I started noticing some kind of electrical interference when power was removed from the switch coils. The interference would almost always cause the indicator lights on the relay boards to flicker, and it would sometimes cause relays to activate unintentionally. Here is what I did to get rid of the problem:
1) The problem only occurred when I had power going through the relay outputs, so I first changed the power supply that I was using for the Atlas switches to a DC transformer with a capacitor across the inputs. This improved the situation a little but did not eliminate the problem.
2) Next I changed the way I was powering the Arduino. I had been using a 12v power supply plugged into the barrel jack of the Arduino. I switched to a 5v supply that I connected directly to the 5v and ground pins of the Arduino. I also ran power to each of my separate boards directly from the power supply instead of through the Arduino. This change eliminated the unintentional relay activation, but I still noticed an occasional flicker.
3) Finally I added a flyback diode across the Atlas switch coils. This seemed to completely fix the issue. I have 16 switches connected, and they have been working perfectly for a few days.
