Questions about RFiD

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

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.

RFIDs are common in that frequency range, in order to reuse commonly available chips and antennas.

Not likely.

y zigbee.

Because you don't.

The only thing common is the frequency band.

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.

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

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     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

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.

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

(...)

(...)

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

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     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

(...)

OIC. Thanks!

--Winston

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?

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.

(...)

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

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.

(...)

Thanks!

--Winston

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.

Interesting, thanks! I'm more interested in UHF, though.

The software radio is pretty compelling!

--Winston

.

t_intro.pdf

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

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.

_id=3D%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.)

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.

(...)

Thanks for all the excellent info!

--Winston