Questions about RFiD

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Hi,
I've read a book about rfid and i've some questions about (i'm totally
a newbie in this field):
1. a standard for active rfid at 433MHz-850/950MHz-2,4GHz is present
or not?
2. I've read about active rfids based on zigbee (or wifi): i don't
understand why i should use a zigbee/rfid combination and not only
zigbee...EPC and other related data could be saved on end device's
memory, so i should have a zigbee-only wireless network...or not?
thanks

Re: Questions about RFiD

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You'd probably get better answers by just putting your keywors/phrases
from this very question into google's search window. Google DOES have
a search side, you know.

Good Luck!
Rich


Re: Questions about RFiD
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I know, and i've done that search. Google is a great tool, but
sometimes something useful is very difficult to find. If you know any
link that has answers let me know...I've prefered to write a post in
this forum due a lot of experts that help newbies like me.


Re: Questions about RFiD
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RFIDs are common in that frequency range, in order to reuse commonly
available chips and antennas.

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Not likely.


Because you don't.

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The only thing common is the frequency band.

Re: Questions about RFiD

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At least one.  Perhaps thousands.  There's also products in the low
frequency band (somewhere in the 30-300kHz neighborhood) that work
primarily by induction.  That is, if I'm not mistaken, what department
store anti-theft RFID tags use.

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Well, how much does a passive RFID tag cost, and how well does it work
after sitting on a store shelf for a year?  How does that compare to a
Zigbee device that needs to work after sitting on a store shelf for a
year, powered up all that time?

(hint: how much would the batteries cost?  How much more electronics do
you need to implement Zigbee, vs. a little gizmo that squirts out a few
tens of bits of OOK whenever it's powered up?)

--
www.wescottdesign.com

Re: Questions about RFiD

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Commercial tags, as I've designed, receive on 130kHz, but respond back at
433MHz... used for truck and pallet tracking.

[snip]
 
                                       ...Jim Thompson
--
                  [On the Road, in New York]

| James E.Thompson, CTO                            |    mens     |
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Re: Questions about RFiD

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I know there are some that receive at one frequency and transmit back on
the 2nd harmonic, and there are some that work all at one frequency by
changing the Q of their resonator (those are the ones used to tag your
pets).

But that's about as extensive as my knowledge of the market is.

--
www.wescottdesign.com

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One buzzword you need to know is ISM, or more specifically the ISM
band. RFIDs use license free bands that work on worldwide (well to
some degree) frequencies. Some of the edge of the bands don't work in
all countries.

Two schemes can be used. One is to energize with a frequency, then get
back a chirp on that frequency. The other is to energize/interrogate
on one frequency, then simultaneous report on another frequency,
usually in a different band. The frequency difference makes the full
duplex filtering cheaper.

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I had internalized 'single frequency' RFID as operating
slightly differently.  A CW carrier is sent from the
'scanner'. Any compatible RFID tags in the vicinity
would locally rectify and filter the carrier for power.
At some voltage threshold, the tag would change it's
impedance (to the carrier) in step with a code representing
it's serial number and perhaps a text and/or graphics payload.

The 'scanner' sees each of these impedance changes as
an change in the amount of power needed to keep the
carrier at a given output level and converts the
changes into symbols to be sent up the command chain.

Can you add to, subtract from or correct the
forgoing for me?

The two-frequency duplex scheme is a new one on me.

--Winston

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There's a whole variety of schemes... you were almost there... rectifying not
only provides power, but also doubles the frequency... the "talk back"
frequency ;-)
 
                                       ...Jim Thompson
--
                  [On the Road, in New York]

| James E.Thompson, CTO                            |    mens     |
We've slightly trimmed the long signature. Click to see the full one.
Re: Questions about RFiD

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OIC.  Thanks!

--Winston

Re: Questions about RFiD
Thanks for your reply...
I know that a lot of standards for passive rfid tags are present (EPC
Gen2 is an example), but i don't know if standards for active rfid
tags are present (i've read something at 433MHz, but nothing at
850-950MHz or 2.4GHz)....
About Rfid/Zigbee (or something else): at 2.4GHz i've found only
combined solution (nothing about rfid-only network). So i don't
understand why i can't use a Zigbee-only network. Batteries are
present in ZigBee devices and in active rfid tags; micro is necessary
in zigbee for stack implementation: but if i use a combined solution,
micro is mandatory. Micro's memory can be used for EPC code, so: why i
should use a combined solution and not ZigBee/WiFi-only?

Re: Questions about RFiD
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Your scheme is the backscatter RFID. It is harder to demod since
everything is on the same frequency. There were also schemes with the
interrogating frequency was swept and the tag has resonant elements.
Using two frequencies is simpler to demod, especially with a wide
difference so transmit and receive can be filtered.

In my mind, RFIDs are strictly passive. But in the marketplace, RFID
can be anything that talks back, even it it requires a battery.


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Thanks for the info.
I have a box full of LF and UHF tags that I would like
to play with at some point.  It would be cool to know
what scheme they use before I invest in the required
hardware.  First prize would be a website showing pictures
of each of the tags with frequencies and schemes revealed.

That may be asking too much, however.  :)

--Winston

Re: Questions about RFiD
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Some RFIDs are FCC approved. If you have one with a FCC number, then
it is a matter of looking it up in the FCC product database.


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Thanks!

--Winston

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If you go to the FTDI website, they sell a USB RFID reader. Looks like
a good way to start. They also list various "standards" for RFIDs
(maybe ISO, I'd need to dig up the page again). While it is
educational to roll your own, it probably pays to buy a reader and
maybe a few RFIDs and just play a bit. Then see if you can make an
uber reader.

Defcon has done long distance RFID demos. There may be related
documents or videos.

Their lock picking video are impressive. If I ever go to Defcon, I
plan to bring some federal combo locks I was given that the base
forgot the combinations.

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http://apple.clickandbuild.com/cnb/shop/ftdichip?op=catalogue-products-null&prodCategoryID50%&title=DLP-RFID1,+DLP-RFIDTAG

Interesting, thanks!
I'm more interested in UHF, though.
www.rfidjournal.net/Alliance_Lab_Report_intro.pdf

The software radio is pretty compelling!
http://www.ettus.com/products


--Winston

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I've played with SDRs. They work, but they really are only good for
places where you have AC mains. You can't run a SDR in the field
without a notebook PC, which more or less cuts your operating time to
5 hours. I really like a radio that is self contained but with a demod
tap so I can hack on the baseband with other hardware.

Find a RFID reader with a FCC product ID posted online. Then you can
get detailed information from the FCC website. For instance, take

http://www.dlpdesign.com/dlp-rfid-uhf1b-ds-v10.pdf

It has FCC ID XS9UHF1B. From the FCC product ID website, you can get
all sorts of information on the item before you buy it. Occasionally
schematics.

https://fjallfoss.fcc.gov/oetcf/eas/reports/ViewExhibitReport.cfm?mode3D%Ex =
hibits&RequestTimeout3D%500&calledFromFrame3D%N&application_id3D%872983&fcc=
_id3D%%27SX9UHF1B%27

That's an ugly link. Try going to the main search page and enter the
product ID (first 3 letters in one box and the rest in another.)

https://fjallfoss.fcc.gov/oetcf/eas/reports/GenericSearch.cfm

Once you know a manufacturers code, you can just enter that code
(first 3 letters) and get ever item they ever applied to the FCC for
qualification.

If you want to hack, you should get a reader with external antenna
port so you can roll your own high gain antenna.  For 900Mhz parts,
you could probably build a biquad antenna. They are easier to use
covertly than a yagi, though there are off the shelf yagis and simple
whip for 900MHz ISM.

Sometimes on the FCC website you can find a test port on the PCB where
you can solder a SMA and convert the item to an external antenna.

I don't know what country you are in, but in the US, I often see yagis
mounted from highway signs pointed downward. I assume they are
sniffing RFIDs. Many localities have electronic signs indicating the
travel time between points, and are probably just crowd sourcing RFIDs
used for bridge/road tolls.

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Thanks for all the excellent info!

--Winston

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