cool forum, just got my uno and saw project for connecting arduino to rfid reader on instructables. is there a multi-rfid reader that can read 10 tags placed 2.5 away from each other and read each tag corrently? what about connecting 10 rfid readers next to each other? is there any problems with interference or way to shielding so reader does not read the tag next to it?
that's 2.5 cm!
Which RFID reader are you proposing to use. The affordable ones are very limited range - as in near contact.
Tags an inch apart might as well be a foot or a mile apart.
Not sure what a multi-rfid reader is, But I build a door lock using a APSX RW-210 RFID Reader/Writer Module (TTL) three years ago and it been running every day since then with no problems.
thks for taking the time to reply, what i was thinking is an arduino based rfid reader (125 kHz) with multiple antennae (for example, multiple points to control 10 doors in a building). I was hoping to use the following instructions: http://www.instructables.com/id/Arduino-and-RFID-from-seeedstudio/.
does anyone know how to connect the 10 antennae to one rfid reading board? Or Would I need 10 rfid readers (with 10 antennae), if so, how would these 10 boards be connected to the arduino? :o
You need 10 rfid readers, not 10 antenna.
The output of the rfid reader goes to a digital pin. Use NewSoftSerial to read the data from the digital pin.
Note that you can only have one instance of NewSoftSerial active at one time. Data that arrives for another instance (on another pin) may (probably will) get lost.
What exactly are you trying to do?
what i'm trying to do is apply tags to merchandise (watches) so that I can keep track of how many times an item gets picked up. each item has a tag...can this be managed with one rfid reader, or do I need to have 10 readers, one for each watch? trying to write a script that counts how many times each item is picked up. any ideas? :
Lookup Feig rfid on Google. I have been sent the data sheets for an rfid reader that can multiplex 8, maybe more, antennas. I don't have time at the moment, but I will post a link in a few hours.
Looking at your original post, I infer that you want to read a small stack of rfid cards which are all in one place, not have an Arduino at the "heart" of a "network" of rfid antennae, the antennae being in different locations, e.g. front and back door of a building.
If the former... read all the tags in a stack of cards... I don't think it can be done. Believe cards must be presented one at at time. Multiple antennae all in one location would not be clever enough to "take a card each"
The part number of the part I posted about earlier is.. ID ISC.M02.M8-B but it is buried so deep in the Feig website I can't find it again. It is definitely available because they sent me details about it after I sent them a query about multi rfid readers a few weeks ago.
Edit: take a look at the video here Ideo's C6O REDUX Brings Mixtapes Back | Arduino Blog
great post and find. I went to one of the source pages: Relational Databases for Non-Coders - How do You Code a Relational Database? | AppMaster. It says: The electronics design replicates the 6 antenna 8 times resulting in 48 antennas covering the 10.5” square printed circuit board. What does that mean? Can an arduino mini handle 6 antenna? 
Love the RFID-tags-to-specify-music on a conveyor belt idea! Funky. Not really "necessary"... Winamp is just fine for actually LISTENING to a sequence of songs... but FUN!!
Anyway... back to the matter under discussion....
I think the project cited relies on the fact that it "doesn't matter" if ALL the cards in the bunch placed on the "table" are read... which is fine for that, but not great in other, similar projects.
What the cited project seems to do is mount many antennae in NEARLY the same place, put many cards near the many antennae, and rely on the fact that even though each antenna reads only one card, most of the cards will have been read by at least one of the antennae.
Seems to me that such a scheme would have pretty limited uses... I would be the first to agree that many of MY projects are of limited merit... but I think we need to determine whether there is a way to RELIABLY read multiple cards all presented at the same time in nearly the same place. Multiple antennae may be an answer to picking up some, even most, of the cards... but reliably read them all... I don't think so. But if someone can show a way, it would be of interest!!
The arduino communicates with the reader, the reader deals with the antennas, so if you get a reader that multiplexes several antennas then that number of antennas can be read by using possibly, 4 pins of the arduino.
The only rfid readers I have used (ibtechnology mifare readers) have needed tx, rx, cts & 1 other input connection that registers a valid card within range of the antenna.
The readability of the cards in close proximity will only be discovered by experimentation, unfortunately my project had the plug pulled on it before I got that far and it is something I would have liked to have done.