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RFID question — Parallax Forums

RFID question

redwindredwind Posts: 3
edited 2011-01-26 11:19 in General Discussion
I am looking to automate a dog door. I have noticed that a lot of people have used motion sensors to do the job but for me that wont work since I have a 3 year old running around plus I am also doing this to keep other animals out and the motion sensors would lift for them too. so I decided to go with RFID but the problem is that you have to be with in a few inches to the reader. If I am correct the distance is within the card (correct me if I am wrong) and I need a a tag the will work about 2 feet away from the reader. Does anyone know of where I can find one with that range?

Comments

  • FranklinFranklin Posts: 4,747
    edited 2011-01-25 21:28
    The distance depends on the type of card(its antenna) the reader and the frequency of the two, also power. There is no magic but if you were to build your own reader you might get better range.
  • redwindredwind Posts: 3
    edited 2011-01-25 21:38
    thanks i get the concept of RFID but this is the first time i am actually digging into it. how about an antenna is there such a thing for RFID
  • Mike GreenMike Green Posts: 23,101
    edited 2011-01-26 07:39
    The range is low for several reasons. The biggest reason is that the RFID reader has to supply power to the tag by transmitting it. The tag has to receive it as an RF signal, convert it to DC, then generate its own signal which it transmits back to the RFID reader. The amount of power available falls off rapidly as the square of the distance.

    The RFID reader that Parallax sells uses a signal at roughly 125KHz. There are other frequencies used for RFID tags. Some have greater range, but require more sophisticated (and expensive) equipment, both for the reader and the tags. Do a websearch for "RFID" and do some investigating. That will give you some idea of what's available and how much it costs.

    At 125KHz, the antenna is the coil you see in the RFID reader (and tags). Theoretically you could attach an external antenna, but it would be huge and thoroughly impractical.
  • skylightskylight Posts: 1,915
    edited 2011-01-26 11:19
    This seems to be as much about design as being technical, as it's a dog and presuming the tag will be on it's collar why don't you observe how it approaches the door and the best position for placing the reader would be so that the tag brushes up against it, funny as this might seem, as it's a dog perhaps you could train it to place it's head in a certain place near the door with a treat so that it always places the tag into an optimum place?
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