We have two cats

Gus

and Penny:

They live indoors and outdoors. Some other cats from the neighborhood learned that the food my wife buys is better than what they get from the owners, so regularly we find other cats in our garage feasting on the food.

I'm a programmer and I like to build stuff... so I had to build something to solve the problem.

Meet the Tweeting Cat door:

Each cat has a small RFID tag on the collar. When a cat is in the close proximity of the door, a small RFID reader reads the tag and if the cat is authorized, a servo will unlock the cat door. The RFID reader and the servo controller are connected to an old laptop. The software on the laptop is written in Delphi and for each "cat door event" is sending a Twitter message and a picture to twitter.com:

1. USB Hub. Used to connect all the components together.

2 . Micro switch. The micro switch is connected to the joystick hardware. When the cat door is open, one of the joystick buttons is pressed. This helps the software decide if the cat went in or out.

3. Cat door.

4. Servo. I used "HiTec HS-322HD Standard Servo".

5. This originally was the electronics from a joystick. Currently, I use the electronic board from a guitar made for the game "Guitar Hero". The original joystick hardware burned after few days of use. 

6. Servo controller. I used "PhidgetServo 1-Motor". 

7. RFID Reader. I used PhidgetRFID. 

8. There is also a Webcam (not visible in the picture) used for the "Tweeting cat door". 

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Listen to the story of the Tweeting Cat Door on Canadian Public Radio: cbc.ca

Tweeting Cat Door on Spiegel.de

Here is a funny story. My son, Vlad, (he's 11) always plays pranks on me... and one Saturday while I was sitting on the toilet reading the news on my handheld internet enabled computer (Nokia N810),  I heard him saying to my wife "I saw a weird animal outside, around the cat door dad made!". Curious to see what he is talking about, I fired up VNC and connected to the laptop that handles the cat door and.... here is the picture I found...

I didn't know how to get out of the bathroom fast enough to see what the heck was the animal in the picture! Of course, when I got out, he was laughing and I realized that he's the monster!