I made this dog door out of laser cut acrylic, spring hinges, a servo (hobby grade), an arduino, and a hand full of M3 socket head screws. It automatically opens the dog door at 7:30AM every morning to let the dogs into the backyard. When pushed closed, the door trips a limit switch and the servo rotates into the CLOSED position. If the door needs to be opened again before 7:30AM, there is an override button mounted on the wall that rotates the servo back to the OPEN position. As a safety feature, the door cannot be closed automatically, so that no pets get locked outside.

Features:

Spring hinges

Hobby Servo for holding the door

Door sensing limit switch

Push button release

RTC with battery backup to accurately keep time

Arduino

Next Generation Features:

Door status reporting over wifi

Daylight Savings time mechanical switch

OTA programming