PN532 NFC/RFID reading multiple tags

[paulofloresjunior]

Hi,

I have one PN532 NFC/RFID and I need to read multiple tags to know how many objects are near to PN532.
In reading program example (from Arduino SDK) I can reading 2 tags in same time, but I want to read all tags, how can I do that?

Thanks in advanced,
Paulo

[ktownsend]

You can only physically read max two cards. The spec and HW is defined tha way.

[paulofloresjunior]

You can only physically read max two cards. The spec and HW is defined tha way.

Do you know another hardware that can do that?

Thanks,
Paulo

[ktownsend]

It's not a HW problem in terms of the chip, it's a limitation of the NFC and appropriate ISO standards. Being able to read two cards at once is already an added feature ... I don't see how you can read a stack of cards, so no ... I don't know anything that can do that.

[GordieGii]

This card seems to be able to handle up to 15 at a time (http://www.dlpdesign.com/dlp-rfid2-ds-v10.pdf) so I don't see how it could be a limitation of the protocol...

So is it a limitation of the chip or the library?

Gordie.

[dennisma]

There is no RFID limitation in the spec that I have ever heard of. On the contrary there are readers that can read tens/hundred RFID tags simultaneously.

Here is a post from the RFID Journal that briefly discusses this http://www.rfidjournal.com/article/view/7853. It states:

One way to understand this is to think of a teacher trying to take attendance in a room containing a lot of students, but with no list of the children's names. The instructor might announce, "If your last name begins with the letter A, stand up." If five children stand up, he or she might say, "If your last name starts with AA, remain standing. If not, sit down." That might leave one child to communicate with. Then the teacher can say, "If your last name starts with AB, please stand up." And so on.

RFID systems have a variety of different means of doing this as rapidly as possible. But essentially, they all come down to the same processes of polling the tags, and narrowing down the requests until the reader can communicate with one tag at a time. It happens very quickly, so it appears you are reading 50 or so tags at the same time, when, in fact, the reader is communicating with only one tag in any given interval.
...
I have seen the firm read 100 tags on documents stacked one on top of another. I have also witnessed NXP Semiconductors interrogate tags on 90 drug vials without a problem.

[GordieGii]

OK. I'm new here. How does one get a decisive answer from Adafruit re this subject.
Does the chip / board(s) / library support 'simultaneously' reading from more than two tags?

Gordie.

[adafruit_support_bill]

How does one get a decisive answer from Adafruit re this subject.
Does the chip / board(s) / library support 'simultaneously' reading from more than two tags?

Ktownsend is the designer of the board. His answer was at the top of the thread:

You can only physically read max two cards. The spec and HW is defined tha way.

[GordieGii]

Oops! Didn't realize. Please accept my apologies.

Then ktownsend is the right person to ask.

So as I understand it, the limitation must be that the chip is designed for phones, not inventory readers, and therefore has only implemented resources enough to keep track of two tags at a time (but can chat with other phones). Hacking the library isn't going to help. So if I want to be able to read more than 2 tags at a time, then, unless there is a more (or differently) capable chip that could be subbed onto this shield I will have to get something else. (...like the DLP-RFID2)

Does that sound accurate?

BTW: Is the library for this card open source? I wouldn't want to write an interface from scratch if I could modify an existing one. (...by which I mean "I wouldn't want to get my son to write an interface from scratch if I could get him to modify an existing one." I'm more of a hardware guy.)

Gordie.

[adafruit_support_bill]

I'll let Kevin answer your questions about the chip.
But to answer your last question: Yes, all our libraries are open source : https://github.com/adafruit/Adafruit_NFCShield_I2C

[ktownsend]

As stated, you can only ever read two tags at most with this chip. It's a fixed in stone HW limit that no amount of firmware hacking will get around.

RFID is a very big field and there are many solutions for many problems (different protocols, different frequencies, etc.) ... NFC is intended for very short range communication, not something like inventory control where other RFID frequencies and standards are a much better match.

Based on your description, this probably isn't the chip that you want or need.

Kevin

[ktownsend]

There is no RFID limitation in the spec that I have ever heard of. On the contrary there are readers that can read tens/hundred RFID tags simultaneously.

The discussion was specifically for the PN532 shield and NFC, which does have a very specific fixed 2-tag limit.

Talking about generic RFID isn't particularly useful ... the possibilities are all over the map. But NFC is a very specific segment of the (very wide) RFID landscape, with very specific limitations and possibilities.