Step 4: Electronics
For the electronics, a simple on/off switch would have worked. But I wanted to get a little fancier and control the timing of the doors opening and closing. I made the circuitry from components that are readily available at Radio Shack and Sparkfun.com. The circuitry just waits for the button to be pushed then switches the air valve on so the door will open. After a few seconds, the valve switches back off and the door closes.
I mounted a DIP socket, a relay, and a few other components on a Radio Shack perf board, and placed the whole thing inside a plastic junction box. I also wired in two AC power switches, one supplying AC power to the wall adapter for the circuitry, and the other supplying power to the compressor in the attic. I wanted the whole system to be enabled and disabled from this "control panel", including the air supply.