I took a piece of cardboard and some unused 1/8 inch rivets, poked the non-rivet end into the cardboard and set the Relay Shield on top of them using the mounting holes. Not a good long term solution, obviously, but it kept the boards from sliding a round while I was wiring everything up.
This project is going to need a much more solid base because the wires for the irrigation system are pretty heavy. I'm thinking about getting a nice, thick sheet of clear acrylic for mounting. I will also have to go find a screw terminal block and use that in between the relay boards and the irrigation wire. Fun! And, I also need to figure out how to get an ethernet connection into my garage where the current irrigation controller lives. Heh.
Arduino Pin Use Limitations: Pin 10, 13I have a total of 12 relays I can control with the Relay Shields, and I was hoping to use pins 2 to 13 for that purpose. Well, trying that didn't go so well. Apparently the Arduino Ethernet Shield lays claim to pin 10 and so I cannot use it for output. Also, pin 13 (which is connected to the ADK board's LED) gets flashed a lot during program uploads. So, if I connect one of my relays to pin 13, it gets opened and closed dozens of times a second while I'm uploading a new Arduino program. That's going to cause unwanted wear and tear on the relay and possibly overheat it as I noticed when connecting the relays to pin 0 and 1.
So now I'm down to using only 10 relays of my 12. That's more than enough for my project, and if I really need them the ADK lot's more digital outputs. I was hoping to be able to control twelve relays with just the pins available on a Arduino Uno though. Maybe I can use the analog pins to control the relays?