[Dale Cook] has cats, and as he readily admits, cats are jerks. We’d use stronger language than that, but either way it became a significant impediment to making progress with an RFID-based sensor to allow his cats access to their litterbox. Luckily, though, he was able to salvage the project enough to give a great talk on RFID from first principles and learn about a potentially tragic mistake.
If you don’t have 20 minutes to spare for the video below, the quick summary is that [Dale]’s cats are each chipped with an RFID tag using the FDX-B protocol. He figured he’d be able to build a scanner to open the door to their playpen litterbox, but alas, the read range on the chip and the aforementioned attitude problems foiled that plan. He kept plugging away, though, to better understand RFID and the electronics that make it work.
To that end, [Dale] rolled his own RFID reader pretty much from scratch. He used an Arduino to generate the 134.2-kHz clock signal for the FDX-B chips and to parse the returned data. In between, he built a push-pull driver for the antenna coil and an envelope detector to pull the modulated data off the carrier. He also added a low-pass filter and a comparator to clean up the signal into a nice square wave, which was fed into the Arduino to parse the Differential Manchester-encoded data.
Although he was able to read his cats’ chips with this setup, [Dale] admits it was a long road compared to just buying a Flipper Zero or visiting the vet. But it provided him a look under the covers of RFID, which is worth a lot all by itself. But more importantly, he also discovered that one cat had a chip that returned a code different than what was recorded in the national database. That could have resulted in heartache, and avoiding that is certainly worth the effort too.
Thanks for the tip, [Gustavo].
I love this and am so jealous of the drive to finish. I ended up on a similar path years ago with an rfid cat feeder that had a fatal flaw. It was not water proof and cats tend to like to puke….. all over it…. leaking in to the electronics. So I wanted to co-opt the already wound antenna and roll my own smart cat feeder. Sadly I only ever got as far as disassembling it and seeing how it was intended to work, and getting an arduino up and running with an off-the-shelf rfid kit with a way to small antenna on it.
This talk may be the perfect jumping off point I need to revisit that project to make an affordable, open-source, smart cat feeder(specifically for wet food).
for completeness, this is the rfid cat feeder I was attempting to mod. The entire ring around it has the antenna embedded in it(with surprisingly thick wire and relatively few coils.) It reads both cat tags and standard rfid tags that can be attached to the pets collar.
https://www.surepetcare.com/en-us/pet-feeder/microchip-pet-feeder
Surepet have a patent on how they read the RFID. I did read through it when I was contemplating an IoT cat flap so I could track which cats were where, but it was just so much gibberish to me at the time. This project may help me understand!
Interesting. When I get a cat refill, this suggests that I should not only have them shipped, but have my vet check that the chip is returning the proper value.
(Even indoor cats should be chipped. It’s one of the best tools for recovering if they get out, get lost, and panic.)
Github repo: https://github.com/decrazyo/fdxb