I bought an automated cat door, but it was overly complicated for my needs (I'm not worried about neighbor cats or raccoons coming inside). It also has a loud motor that randomly activated during the day, which was annoying. Plus, the motor startled the cats. Also, not all cats learned to push their way through the door.
We ended up taping the door open every morning after being awakened by the cats very early.
So, I built this winch system that physically opens the door every morning, and closes it every night.
We can also manually open or close the door using buttons on top - red to close, green to open, blue to stop.
Cases are 3D printed from Thingiverse.com designs. I'm using Arduino Nano, DS1307 RTC, 28byj-48 stepper motor, custom programming.
Images and video didn't work for me, so here are links: