Switching between RFID antennas - one reader 100 antennas - how?

Hi, I would like to connect multiple antennas (more than 100) to a RFID reader and switch between these antennas using a microcontroller. Can anyone point me to the right direction what type of switch can be used for this?

Thanks Yve

----------------------------------------------------------------- Yvonne Vanderbild mail: yvonne.vanderbilt@@@hotmail.co.uk

formatting link

Reply to
yvonne.vanderbilt
Loading thread data ...

yvonne.vanderbilt@@@hotmail.co.ukhttp://www.flickr.com/photos/7432253@N03/

formatting link

Frank

Reply to
Frank Raffaeli

yvonne.vanderbilt@@@hotmail.co.ukhttp://www.flickr.com/photos/7432253@N03/

Thanks for the link Frank, I am not looking for a ready made professional switch module. Would it be possible to use e.g. the ADG732 to switch RFID antennas (13,56 MHz or 125kHz).

formatting link

Thanks Yve

Radio Frequency Identification - Wikipedia

Reply to
yvonne.vanderbilt

yvonne.vanderbilt@@@hotmail.co.ukhttp://www.flickr.com/photos/7432253@N03/

It should be ok for 125 kHz, but the ON-switch capacitance is large, so you're going to lose some signal at 13.56 MHz.

I've had some good success with discrete switches using this part:

formatting link

You could also try the many flavors of T-gates (analog switches) like HC4051 DG221B .... etc.

Frank

Reply to
Frank Raffaeli

yvonne.vanderbilt@@@hotmail.co.ukhttp://www.flickr.com/photos/7432253@N03/

Depends if you want to use the antannas for receiving or transmitting . A few 100 mA and 10s of Volts may be a bit much for a CMOS switch.

Wim

Reply to
Wim Ton

Korrrrrrrrrr!

I know nothing about RFID but if you've got some used bike seats you'd like to sell??????

Korrrrrrrrrr!

Anyway, if your tags were a bit clever isn't there some way you could random adaptively time division multiplex some sort of thing that goes like.

Receiver

'What's the answer.... boys?'

Transmitters

'Me, me, me'

Receiver

'Garbled, shut up for a random time'

Transmitter(s)

'Sulk, purlease whip us'

'What's the answer, boys?'

Transmitter

'Me'

Receiver

'Gotcha'

Transmitter (To Himself)

'OK, I will now shut up for a bit longer, hurry up and whip me again'

Receiver

'What's the answer, boys?'

etc

Korrrrrrrrrrr!!!!!

DNA

Reply to
Genome

100 antennas for one reader is getting a little outa hand in my opinion -- you might consider independent readers with 4-8 antennas + a microcontroller (which you need anyway to handle antenna switching), and interconnect with ethernet or multi-drop serial. i'm assuming the antennas will be at least somewhat seperated, and you are creating a huge headache backhauling 100+ coax feeds, not to mention coax losses in the longer runs.

there are schematics and code online for building MCU based RFID readers for just a few dollars in parts, and adding an 8 channel multiplexor to the front end of one of those should be simple enough. RS-485 is easy enough to cope with for the multidrop connection, or get an MCU with on chip ethernet.

Personally -- I would consider some of those 900mhz data radio modules for the backhaul link -- thats the setup we are doing for a warehouse RFID system -- 4 antennas per reader with 900mhz RF backhaul -- 50 readers for a total of 200 antennas covering 20 dock doors, 5 fork lifts, and 25 key transit points throughout the warehouse. We had some real fun setting up so that the readers from one dock door didnt pick up traffic from adjacent doors :)

Reply to
John Barrett

Thanks guys for you suggestions, a bit more background on what I am trying to build: I try to identify chess pieces on a 8x8 chess board. The pieces have an implanted RFID glass-tag which I want to read from below the chess board. The board is just a few millimeter thick and made of plastic. One solutions of course is to move the antenna on an simple xy slegde but I want to aviod moving/mechanical parts. I also want to use RFID and not any of the alternative techniques like Reed- contacts, etc. So, the 64 antennas are on a regular 8x8 matrix, one below each field which is 5x5cm. What ever the antennas pick up will be processed by a microcontroller this gives the option to resolve ambiguities because the MC knowns at least most of the time where the pieces stand and only the piece that has been moved needs to be found. However, the main thing I am worry about at the moment is how the MC switches the antennas. One of the few things I konw about RFID is that the antenna when in resonance carries up to 100V which is too much for most analog switches and multiplexer.

Yve

----------------------------------------------------------------- Yvonne Vanderbilt mail: yvonne.vanderbilt@@@hotmail.co.uk

formatting link

Reply to
yvonne.vanderbilt

thats too close -- the antenna in any square will likely pick up the chips in ALL the pieces !! not a bad idea in general concept -- but off the shelf RFID hardware has too much range for this particular application -- you need something much more tightly coupled and lower power -- it can still be based on RFID technology, but scaled down for the millimeter ranges that you are talking about -- I would SERIOUSLY look at the MCU based rfid reader schematics out there -- at least you have the circuit so you can tune the power such that you only activate the chip in the correct square. The antenna coils need to be scaled back -- less turns, such they create less field to activate adjacent chips, and only activate the closely coupled chip in a given square.

Since you are passing AC signals to the antennas, you could use 16 triacs to create the 8x8 matrix switch -- 8 for each row, 8 for each column -- the power should be low enough that the partially connected antennas will not activate their chips.

Here is a website with an MCU based RFID reader including source code for the MCU.

formatting link

Reply to
John Barrett

formatting link

Just an additional thought -- use ferrite cores for the antennas to direct the field more vertically -- like a stick antenna -- short piece of ferrite with a few turns of wire around it.

Reply to
John Barrett

I'd try it with pot core halves. Done that in the past, worked great and it's cheap.

Yve: At such short distances I'd operate it at lower signal levels so you don't run into lots of volts. Also, you can limit that with diodes if needed.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

RFID antennas are not 50 ohm, so the standard RF switching gear won't do. On the other hand, a cmos switch would probably be OK.

It will be very lossy, but I understand that short range is actually a benefit in your case.

For your chessboard, consider using a matrix arrangement.

Using core material and smaller coils is probably a good idea.

Kind regards,

Iwo

Reply to
Iwo Mergler

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.