I finally got around to joining BYC, although I've been using its resources for almost a year! haha. This is my version of an automatic chicken door. Just thought I'd share. It works flawlessly, and its never locked a chicken out in the cold. As long as the light inside the coop stays on after the sun goes down, the chickens head inside as soon as its dark. Which is good because lately its been dipping down below -50'C here. Yes you read right, -50'C. The door is just plywood, it is operated using a 12volt linear accuator bought from princess auto for $60. It has internal limit switches that stop its movement in and out. I wired up a simple DPDT 120volt relay to a lamp timer that switches the 12volt polarity for up and down operation. (red+ black- it goes up, red- black+ it goes down) Here is a similar circuit to what I came up with that works great. The Vcontrol is my 120Vac timer circuit, and the Vmotor is a constant 12Vdc.