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RFID Reader decision

Greg Hitz
Prodigy 20 points

Hi,

I'm looking for some advice on what RFID technology (if any) would best suit my needs. I'm designing a Raspberry Pi-based automatic unlocking system for my house that will unlock the front door when someone with an RFID tag is near the door (specifically, they shouldn't need to take the tag out of their pocket). I have plenty of room for a large reader antenna but I would need to achieve a fairly large range (2 meters or so). Ideally, I could use the sticker tags and attach to the back of a cell phone (or in the future use cell phone NFC).

I've been looking at 13 MHz readers, but I'm having trouble spending the money without assurance that I'm on track. Since this is just a home tinkering project, I'm less concerned about top notch security and RFID encryption. Keeping a low budget is important.

It seems the TRF7970 would fit my needs. Am I off-base thinking that all my goals can be met with this device or even at all? The only price I found for this device was an incredibly reasonable $90 on Amazon (http://www.amazon.com/Reader-13-56Mhz-Multiple-Protocol-TRF7970/dp/B006WS5EGE/ref=sr_1_1?ie=UTF8&qid=1359272235&sr=8-1). How much would this cost from TI?

Thanks,

Greg

  • 0
    TI__Guru* 91306 points

    Greg - you will never get that kind of distance out of passive HF tech, let alone using unknown tag orientation. You should consider changing you requirements to make the person present an HF or LF card or fob (like what all the DDL are using today) or move to a more advanced idea like what is done for car access, whereby a downlink is sent over LF and the tag (with a 3D antenna) is responding with UHF. (could be 433MHz, 868MHz or 902-928MHz, depending on what country you are wanting to operate in)

    http://www.ti.com/solution/car_access_system 

  • 0 in reply to Josh Wyatt
    Prodigy 20 points

    Josh,

    Thanks for the reply! I'm not married to an HF system but I would want passive tags. This ability seems to be integrated into libraries with RFID gates that read passive tags of unknown orientation. I think I could position the reader so even a few foot range might be enough, similar to the gates at a library.

    Greg

    PS - I don't mean to be hardheaded. If you again say what I'm looking for isn't possible, I'll accept it.

  • 0 in reply to Greg Hitz
    TI__Guru* 91306 points

    the library systems i am very familiar with - have a look at this ==> http://www.ti.com/rfid/docs/manuals/appNotes/HFAntennaDesignNotes.pdf (section 8 in particular) as it relates some knowledge about reading HF tags in unknown orientations - this kind of a system i have miniturized, too - but for a doorways and the like, with HF, you would need a pair of antennas like these ==> http://www.feig.de/en/products/obid/product-areas/obid-i-scan-hf/long-range-antennas/id-iscant1700740-clear-gate.html and a high power reader to go with it (Feig also sells these and we used these in conjunction with the antennas described in the design notes pdf link. You would also want to use the largest tag possible as well - usually our ISO15693 45mm x 45mm square tag or larger works great in these kinds of applications. The drawback of course is the cost - for a home, usually no one can spend 10k+ just to get in their house automatically - this is why either using a known orientation approach (like making the user present a tag or fob) is best way overall - you can still get good range (using the TRF79xx parts) using this approach if you choose right size antenna (maybe 300mm x 300mm max, for about 10-12" range), with ISO15693 tags of reasonable size.