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Building a RFID Reader
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Rob_ View Drop Down
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Joined: 20 March 2006
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    Posted: 20 March 2006 at 5:30pm
Hey Amal,

I want to build a rfid reader for a university project and was wondering if you (or anyone else) have an info on building the reader?

I could easily go out and buy a reader but that wouldnt be much of a project , would it ..

We were originally thinking of operating at 13.56MHz but have found that some dev kits are over $2000!! (and they are quite complex!)

Been checking out the Phidget RFID reader and it doesnt seem like their are many components on the board.

So any info on this topic would be much appreciated!

Rob
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amal View Drop Down
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Joined: 22 November 2005
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Points: 2065 		Post Options Post Options   Thanks (0) Thanks(0)   Quote amal Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2006 at 5:40pm
You're right, the component count is quite low. Building a low frequency reader is fairly trivial. You can buy pre-tuned antenna coils and IC chips that contain all the interrogation and data decoding functions inside them. Check out this post for more info: http://www.rfidtoys.net/forum/forum_posts.asp?TID=29&PN= 1

If you really want to get into the guts of how RFID works, start researching all the different types of "air interfaces" there are for RFID tags and readers. The air interface defines all the specifications for communication between tag and reader, including frequency, data encoding scheme, etc. You can utilize the parts available, or you can make it as complicated as you want by building out the functions of these ICs by hand.

I know a guy who has done just that in the low frequency range tags... I'll see if I can't get him to join the forum and chime in with his experiences.
Amal ;)
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Rob_ View Drop Down
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Points: 3 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rob_ Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2006 at 11:05pm
Is it actually any harder to build a high frequency reader than a low frequency one?

if so which parts are harder/more expensive?
eg. transmitter, receiver, antenna.

ive been getting mixed answers from websites about reader range and want to clear it for good.

A higher frequency can read a greater distance. Correct?
(Using similar power etc.)

EDIT: We need an operating range of about 50cm between reader and tag. would this be possible with a low frequency reader of bout 134kHz?


Edited by Rob_ - 20 March 2006 at 11:23pm
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amal View Drop Down
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Joined: 22 November 2005
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Points: 2065 		Post Options Post Options   Thanks (0) Thanks(0)   Quote amal Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2006 at 7:34am
Generally speaking, the higher the frequency the greater the range. It's a very general statement, but still basically true. Another very generally statement that happens to usually hold true is the higher the frequency, the more sensitive communication is to metallic and liquid interference.

Building an HF reader is more difficult only because of the data encoding and feature set employed by higher frequency RFID tags. The communications protocol between HF tag and HF reader is generally more complicated, with things like read/write, anti-collision, etc.

I can tell you that you will have a difficult time getting 50cm out of even 13.56MHz HF technology. People pay good money for commercial systems that work at that range. Range like that might be possible on 13.56MHz if you had a high powered reader and a pro antenna. You might look into 400MHz - 900MHz technology to get that kind of range.



Edited by amal - 21 March 2006 at 7:35am
Amal ;)
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abraradib View Drop Down
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Points: 7 		Post Options Post Options   Thanks (0) Thanks(0)   Quote abraradib Quote  Post ReplyReply Direct Link To This Post Posted: 23 March 2006 at 6:31am
hi amal.. I am thinking to integrate both LF and HF reader that might be able to read both frequency at mostly in the same time. Is it possible to do that? I am not gonna build the reader from the scratch but plan to use from of-the-shelf product. If it is possible, which product do you suggest that might be easy for the interoparability for the project like this??
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amal View Drop Down
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Points: 2065 		Post Options Post Options   Thanks (0) Thanks(0)   Quote amal Quote  Post ReplyReply Direct Link To This Post Posted: 23 March 2006 at 9:47am
Originally posted by abraradib abraradib wrote:

hi amal.. I am thinking to integrate both LF and HF reader that might be able to read both frequency at mostly in the same time. Is it possible to do that? I am not gonna build the reader from the scratch but plan to use from of-the-shelf product. If it is possible, which product do you suggest that might be easy for the interoparability for the project like this??


Check this post: http://www.rfidtoys.net/forum/forum_posts.asp?TID=29&PN= 1

In it, there is a link to a cheap Texas Instruments LF/HF reader module. It only works with 134KHz TI low frequency tags, but it's basically what you're looking for. The direct like to the reader is here: http://rfidusa.com/superstore/product_info.php?cPath=37_31&a mp;products_id=284
Amal ;)
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abraradib View Drop Down
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Points: 7 		Post Options Post Options   Thanks (0) Thanks(0)   Quote abraradib Quote  Post ReplyReply Direct Link To This Post Posted: 23 March 2006 at 10:47pm
Ok thanks amal.. 1 thing I wonder IF i can integrate the HF and UHF reader together?? Is it possible?
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amal View Drop Down
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Originally posted by abraradib abraradib wrote:

Ok thanks amal.. 1 thing I wonder IF i can integrate the HF and UHF reader together?? Is it possible?


Hmm, I've not seen any OEM parts or boards or readers out there, but it doesn't mean they don't exist. If you are building your own readers from scratch, I'm sure you could do it. The only thing you'd have to do is use two different antennas, one for HF and one for UHF.
Amal ;)
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Rob_ View Drop Down
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Points: 3 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Rob_ Quote  Post ReplyReply Direct Link To This Post Posted: 11 May 2006 at 8:25pm

After a bit of mucking around we have decided to up the frequency of operation from 13.56MHz to 915MHz due to a limited read range.

As we are operating in UHF we have had to change from inductive coupling to backscatter as a means of communicating with the reader.

This means we have to use a directional coupler in order to receive the signal. been reading alot on directional couplers, but not sure which one is valid in our case.

the 180 degree directional coupler looks like the most relevant but not too sure.

Ive included a pic to fully demonstrate it

As i understand it, the antenna is transmitting and receiving the signals at the same time. and the received signal is going to be relatively weak compared to the transmitted signal, so its hard to seperate the signals

the info that i have been reading bout the 180 degree coupler seems to say that it will split up the incoming signal into two signals or combine two signals into 1.

What i need (as shown in pic) is be able to direct the transmitting signal to the antenna and direct the received signal to the receiver module.

What is the correct directional coupler to use?

Thanx
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