Let's Make Robots!

The cheapest identification method (an alternative to RFID)

Hi all!

I am very beginner in robots making. I have an issue with my 2 cats (one of them). He eats to much and gets fat: when he finishes with his ration, he switches to another bowl:)

So I decided to build up an automatic cat feeder equipped with recognition system to analyse which cat is near the feeder. I have some ideas on mechanical matter of the device and need to learn a lot about electronic. But I have already stuck with the decision how the system will recognise the cats. I had an idea to make some kind of weight scales, but I thing this is not the way I should follow. Face detection system is also toщ complicated, if not impossible for me. So the best way I can see is to use something like RFID. I can't use RFID because the scanner price is too high, and I will need two of them (one for each feeder).

Can anyone give me an advice what will be the best in my situation?

Thanks in advance.

BR, Yakov.

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Thank you. Yes, I have considered that, but in that case the plate should be that big so the whole cat can step on it with all 4 paws, but my kitchen is not so big:) And I am afraid I will myself step on it on occasion very often, which finally might return me back to start thinking on some other way... and the weight difference is not so significant actually although it is.

I have checked web again and finally found that some of the readers are not so expensive and can be purchased for about $5-10. The thing is that the maximum distance of operation is in the range of 5-10 cm. I might have to think about it, and contrive the shape of the feeder in the way so the reader won't be an obstacle for cats.

Anyway thank you very much for your reply. It is so nice I am not left alone with myself! If you have any other ideas I'll be glad to hear from you!

You need to realize that different tags/tokens have different read ranges. Physical size of the tag is a major impediment on the range. Sparkfun has a decent video about the ranges of different tags that they carry.

I thought the antenna of the reader is a major item in this matter. I have read out many web sites today, and to be honest the more I read the more questions I have))) Everyone say that the strength of the reader antenna depends on its size (and of course voltage it is powered with, and so on). So they say that the signal range is equivalent to the antenna diagonal (for 125 kHz and 13,56 Mhz). So if I use the antenna with the diagonal of 10 cm it will be enough for me. I've already changed the design of the feeder in my mind, so I guess it should work.

Soon I will try to transfer my idea onto the paper to be able to ask further questions to the LMR community, and I'm 200% sure I will have tons of them!)

By the way, could you please share the link to the sparkfun video you mentioned?

Many thanks!

Now I found information on Wiki that you probably meant:

"Tags may be read at longer ranges than they are designed for by increasing reader power. The limit on read distance then becomes the signal-to-noise ratio of the signal reflected from the tag back to the reader"...

Thank you for your usefull and important info! Now before purchase of RFID reader and TAGs I will check the real distance in some local shop I think.


Stick an IR beam across the front of the feeder --either cat breaks the beam and the feeder is activated. Now we know if either cat is in place. From there, just stick a magnet on one of the cats' collars. Now we know if there is a cat there and which one it is.

I had a neighbor once with a cat door like this --all the cats had magnets on their collars and thus, the door kept all the squirels and the like out.

Thank you for the advice. This is good idea. But I think I will stay with RFID, therewith I found very cheap and standalone device (see my previous reply).



That's really cool! Thank you.

This is good idea (design) how to ensure RFID reader can always see the TAG and it is not necessary to have a big range one. By the way I found RFID stuff for acceptable price: http://www.rfidadvance.com/#!home-search. I already receive payment details. So I have to take a final decision now. Seller stated 4" operation distance, more than enough for me))) As soon as I get it, I will post new questions.