I am currently building a smart cat door. One of its functionalities is that it keeps the door locked until our cat comes close to it, then it unlocks the door.

I tried using RFID, the RC522 because I read that it can work fr a range of 1m. But after testing, the max range I could get out of it was less than 10cm.

After doing some research I found out that the protocol used in the RC522 can't do more than 10cm.

Another solution I came up with was to use Bluetooth instead, but the problem with Bluetooth is that it has a long detection distance for our application (with class 2 having a range of 10m). This will mean the door will detects the cat even if she is just setting in it's vicinity and we don't want that.

Is there any other sensor combination that can accomplish this task?

  • It doesn't have to be RFID or Bluetooth.
  • It has to detect the cat at a short range, lets say no >2 meters and no <1 meter.
  • It is preferable if the tag/module that goes on the cat is unpowered, or requires low power.

Thank You

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    \$\begingroup\$ cross posted here : engineering.stackexchange.com/q/25721/10902 \$\endgroup\$ – Solar Mike Jan 29 '19 at 13:49
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    \$\begingroup\$ Such a system already exists: 1) if your cat isn't "chipped" already, have that done. The cat will then have a small RFID tag (as small as a grain of rice) in its neck. 2) Buy a PetPorte: store.intl.petsafe.net/en-nl/microchip-petporte-smart-flap I have had this system for a couple of years already. Not cheap but works very well. With other systems the cat would have to wear a collar, cats don't like collars so that collar might "get lost". Also, controlling the range will be a challenge when using bluetooth. \$\endgroup\$ – Bimpelrekkie Jan 29 '19 at 13:52
  • \$\begingroup\$ @SolarMike, I figured I posted it without the related information, and I think it was on the wrong stackexchange, sorry about that. \$\endgroup\$ – MrAbdul Jan 29 '19 at 13:56
  • \$\begingroup\$ @Bimpelrekkie, Thank you for your input, I took a look at the smart flap, however this is for a capston project, and I can't just purchase a finished product and present it as mine. \$\endgroup\$ – MrAbdul Jan 29 '19 at 13:57
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    \$\begingroup\$ If you know the GPS location of the cat and the GPS location of the door, can't you figure out if the cat is near the door? I assume this is a very large cat to be able to haul around all of this equipment and its batteries. \$\endgroup\$ – Elliot Alderson Jan 29 '19 at 15:54

Why such a huge range?

When I built my smart cat door 40 years ago I used RF. I used a 10nF polyester capacitor, and wound a few turns of wire around it, and potted it in resin, including a small hook to attach to the cat collar to make a dongle for the cat. Then built an oscillator at its resonant frequency. I built a flat search 'coil' using veroboard (for stability) with copper wires soldered between the strips, total size probably 25x50 mm. With the cat's head in contact with the flap, the dongle was within 100mm of the bottom of the cat flap, where the search coil was. That's enough coupling to increase the loss of the coil, especially since the orientation of the cat approaching the flap ensured the collar, and hence the dongle, was coaxial with the search coil. Rectify the voltage across the coil, trigger on a dip. The point about using a resonant dongle was it could be relatively small and light.

  • \$\begingroup\$ Now that's keeping it simple. Love it! What was the frequency? Few hundred kHz? (I'm gathering this is basically a grid dip meter kind of thing.) Or perhaps something more like this? quick drawing of another possible approach \$\endgroup\$ – jonk Jan 30 '19 at 6:17
  • \$\begingroup\$ @jonk It was inspired by grid dip, but I was young and not confident of making such a sensitive oscillator, so I made a separate LC osc. Due to the time elapsed, I am probably safe in admitting that it was bang in the middle of the AM band, roughly 1MHz. I kept it low power, the 'antenna' was very inefficient for radio (near field magnetic in fact), the signal was very clean, and not near any strong stations, and I didn't have neighbour complaints in the several years' of operation. \$\endgroup\$ – Neil_UK Jan 30 '19 at 7:23

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