Dobrica Pavlinušić's random unstructured stuff
Hitchhikers Guide to RFID: Revision 48
17n1697c.doc
17n1695t.pdf 17n1695c.doc 17n1692t.pdf 17n1692c.doc 17N1689T.pdf 17n1689c.doc 17n1531t.pdf 17n1531c.doc 17n1522t.pdf 17n1522c.doc 17n1486.pdf 17n1486c.doc 17n1480t.PDF 17n1480c.doc 17n1363t.doc 17n1363b.doc 17n1355t.doc 17n1355b .doc There are many on-line resources about RFID. However, most of them are not well suited for beginners. So, if you just got RFID reader (3M in this case) and want high-level overview of what it is and what it can do, you are out of luck. Until now, that is. This guide should help you decide if RFID is right thing for your library and when you make choice to implement it, how to do it. This document will describe my experience with 3M 810 reader using RFID 501: RFID Standards for Libraries RFID_501.pdf RFID tagBest way to think about RFID tags is like contact-less readable barcode. Our particular tags come in two form: RFID stickers (to be placed on books) and plastic credit-card like cards (we use them for patrons).
Have in mind that established practice is to have different RFID systems for books and patrons (we are use same one). When we asked about using same system for books and patrons, we got reply: "we don't have experience with it". Each tag has unique serial number (SID) assigned by manufacturer and used in RFID collision detection protocol. It looks like hexadecimal number starting with letter E0 like this: E00401003123AA26.
It's best to think of SID as unique identifier of physical tag.
Our initial idea was to use data programmed on chip for everything, and just ignore SIDs, but we found out that there is class of RFID devices which can read ONLY SID from chip (in our case it's photocopying system). Chips have 7 blocks of user data on it, each block with 4 bytes which enables us to store 28 bytes of user specified data on each tag. blank tag3M Manufacturing BlankEasiest case is blank tag, in which all data on chip is 0x55 0 55 55 55 55 blank tag 1 55 55 55 55 2 55 55 55 55 3 55 55 55 55 4 55 55 55 55 5 55 55 55 55 6 00 00 00 00 Generic blankGeneric blank seems to erase only first three blocks with zeros: 00 00 00 00 00 01 00 00 00 00 02 00 00 00 00 while rest of tag will be unchanged including rest of data on tag programmed tagTags programmed with 3M software have following data layout on them: 0 04 is 00 tt i [4 bit] = number of item in set [1 .. i .. s] s [4 bit] = total items in set tt [8 bit] = item type 1 dd dd dd dd dd [16 bytes] = barcode data 2 dd dd dd dd 3 dd dd dd dd 4 dd dd dd dd 5 bb bl ll ll b [12 bit] = branch [unsigned] l [20 bit] = library [unsigned] 6 cc cc cc cc c [32 bit] = custom signed integer This basically means that your barcode or identifier of item or patron can have up to 16 characters (by default numeric, but you can extend that to handle alphanumeric and special character if you need that) and three integer values: branch 0 .. 4095, library 0 .. 1048575 and custom data -2147483648 .. 2147483647.
You might want to use those values to uniquely identify your library and branch so that your RFID tags in books won't collide with other libraries. Writing correct numbers in that fields is not enough. If you want to use 3M software, you will also have to setup it to ignore all other tags which doesn't match your library and branch. securityThere is also single byte called AFI or security which can be changed without accessing content of chip. This byte is also readable by more primitive RFID devices like doors to check if book have been checked out from library.
3M is using 0xD7 (215) value for secured items (door will beep) and 0xDA (218) as unsecured. It seems that all other values are ignored.
As I mentioned before, since we don't have any special values in branch, library or custom field, we have situations in which patron cards get secured when patron walks by checkout counter and 3M software is left in checkout mode. disable tag3M software have option to disable tags. Initial examination showed that it's simply programming of tag with following content: 00 ff 00 00 00 01 00 00 00 00 02 00 00 00 00 03 00 00 00 00 04 00 00 00 00 05 00 00 00 00 06 00 00 00 00 and security set to d7 (this might be value from tag before disabling it, I'll have to re-check this) While 3M software will ignore tags programmed with this content, there is not permanent disabling of tag since it can be programmed using other software. RFID reader deviceReader consists of several part:
Reader is recognized as USB serial device with it's own protocol on serial port. We are mostly interested in it's protocol and our ability to use reader and tags with our custom software.
At first, I assumed that protocol with RFID readers is some kind of standard. So, only solution was to do clean-room reverse engineering, and using that technique I developed perl module which can talk with RFID reader which is available at http://svn.rot13.org/index.cgi/RFID
fetchrss: http://svn.rot13.org/index.cgi/RFID/rss
More informationIf this was too geeky for you here is some additional materials: ISO standard
Related blog posts
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