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An anonymous reader requested a hack today to solve a particular kind of kitty problem. Specifically, the reader wants to know if there's a way to have a cat door that grants access to particular cats while restricting entry or exit for others. Not being a cat owner, I don't follow cat electronics too closely, but I have heard of a project or two that are similar in nature, and I'd like to open this up for further discussion in the comments.
The photo above is from the Flo Control project. This cat, Flo, had a nasty habit of bringing in dead mice to the house. Her owner created a computer controlled system that captures an image of the cat as it approaches the door. The PC does some image recognition to determine if the cat's silhouette is atypical (ie. carrying something nasty) and only unlocks the door if the cat is sans-mouse.
One element that's used in the Flo Control setup is a cat door product made by Cat Mate. They make a few different models of cat doors that require your cat to wear a special collar to be allowed through. These are typically operated by a magnet or infra-red beacon in the collar which is able to mechanically or electronically unlock the door. My guess is that something like this will probably will do the job, but if your neighbors start doing the same thing, there's nothing to keep other cats with a collar from getting in.
A more interesting idea is to use RFID to uniquely identify a particular cat and grant access accordingly. There's a commercial product called Pet Porte that is able to do this with the RFID chip implants that some owners are sticking on their animals these days, but I figure it might be more fun to make your own, perhaps using a tag on a collar.
There are a number of RFID sensors for the Arduino and Basic Stamp microcontrollers. It'd be straightforward to program one of these to accept specific RFID tags and then trip the lock switch in a slightly hacked Cat Mate door. The only problem I see is devising a collar that wouldn't bug the cat and would also place the RFID tag in close enough proximity to the reader. Any readers out there with thoughts on this?
The Flo Control Project - Link
RFID Enabling Your Front Door - Link
Using the Arduino with the Parallax RFID reader - Link
> The only problem I see is devising a collar that wouldn't bug the cat and
> would also place the RFID tag in close enough proximity to the reader.
As I understand it, the bulk of passive RFID tags are antennas to pick up the energy and signal, and a regular sized collar (even one that was twice as wide shouldn't be too uncomfortable) that had a antenna buried in it could conceivably have a range of a foot or so, which, if the receiving antenna was wrapped around the cat door, should be /plenty/. Tear apart a typical store tag and you'll see what I mean. They are picked up at distances of two feet or more by the theft detectors at the exits
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This has already been done :)
http://www.smarthome.com/6191c.html
http://www.smarthome.com/6197.html
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I agree: RFID would seem to be the way to go. Parallax makes a nifty RFID reader that can be hooked up to an Arduino. They also sell poker chip-shaped RFID tags that would be perfect for a collar if you drilled a hole in one of them. I'd suggest a Parallax PIR so that when motion is detected the Arduino would scan for the tag. If you wanted to get fancy you could set the Arduino to powersave until it gets a signal from the PIR, scan for the tag, and then shut down again to keep your battery longer. Now Radioshack actually sells both modules, which is quite convenient, and the surprising bit is that they're only $2 more than the Parallax price on average. A howto on the PRFID is here: http://www.arduino.cc/playground/Learning/PRFID
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Need to do a Cat scan? Consider UHF RFID. Tag size, durability, and range should be exactly what you need. In fact, if you also tag all the mice and birds in the area, you won't need the image recognition system.
I don't know this tag vendor from experience, but it will give you an idea of what is out there:
http://www.rfidsolutionsonline.com/content/productshowcase/product.asp?docid=%7B88132B76-BDC0-4EE7-93BC-6A7B7EA79AB1%7D
As for the reader - full size ones are expensive and overkill. Look for vendors who sell UHF RFID modules and order just the module, or a module with a development kit.
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