I made this robotic cat door for my cat Peewee, who had very specific needs. It’s made from Robotic Mindstorms Lego. It includes four touch sensors, one light sensor, and one motor, and several programs. I made Peewee wear a magnetic collar, which acted as a key that would only let him inside. I lived by myself at the time and would frequently stay out for more than one night, so the cat door needed to allow my cat the freedom to enter and leave whenever he wanted. When wanted in, he simply stood outside of the door. The rare earth magnet in his collar activated a teeter-totter mechanism inside the cat door that caused a change in light intensity, which the light sensor could read. This then activated a program in the RCX (Lego brain) that told the motor to turn on, which caused the Plexiglas elevator-type doors to open until they hit a touch sensor that told the motor to stop and pause and then reverse. A safety switch was included, in case the doors closed on my cat. To get outside, Peewee simply needed to stand in front of the door. A large padded teeter-totter mechanism would move slightly when stepped on, which hit a touch sensor that activated the “open door” program. The whole padded teeter-totter mechanism was designed to roll and fold up like a draw bridge when the door was opened for people to get in and out.