Instructables

RFID Reader Detector and Tilt-Sensitive RFID Tag

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The 'rub'
Want to detect the presence of RFID readers? Want to control when a RFID tag is active or readable? We describe how to do both using bits of copper and card, and some readily available electronics hardware.

Longer preamble
Radio frequency identification ( RFID) is rapidly growing in popularity. RFID tags are found everywhere. They're attached to container freight, in those funny-looking white labels you find in newly purchased books, embedded in many corporate ID cards and passports, etc. The tags have a few common properties: they transmit a unique ID number, are optimized to be 'read' from predefined distances, and are usually small so they can remain unobtrusive or hidden.

RFID readers are used to track nearby tags by wirelessly reading a tag's unique ID (see Figure 4); a tag simply has to be brought into physical proximity with a reader to be read. Readers are mostly used for industrial or commercial purposes, e.g. asset tracking or electronic payment. Wal-mart use RFID tags and readers in their supply chain. The technology is also used in mass transit systems in cities like London and Hong Kong. In Japan, many mobile phones incorporate readers to enable e-money payments in shops and vending machines.

For those of us who want to experiment with RFID, the problem is that the technology is almost always black boxed. That is, the inner workings of a tag and its interaction with a reader is hidden from view, and thus difficult to have much control over.

In the two exercises that follow (building a RFID reader detector and a tilt-sensitive RFID tag), we offer an example of how you can start revealing some of the workings of RFID and thus gain some control over the technology. The two exercises also hopefully show that the technology is relatively simple and how it can be extended to support some interesting interactions. We offer some other possibilities that build on our examples at the end.
 
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lazyafternoon2 months ago

Great project. Thank you for documenting and posting it. I would like to make one and have a few questions for anyone who might know....

1. Does it matter how the LED is oriented when attached to the antenna (anode/cathode)?

2. Do you know of any common stores that use 13.56MHz RFID readers where it would be easy to test without needing to purchase a reader?

3. Can the NFC in a cell phone (mine is a Galaxy S4) be used to test as a reader? Is it strong enough?

4. Does anyone have plans for a 125KHz version?

5. If you don't have an 82pF cap, can you group a couple 333s with a few 103s and be 'close enough'?

6. How important is the spacing between the copper strips?

Any help is appreciated. Thanks!

PinkalPatel4 months ago

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mx285 months ago
hi. I am new to electronics. I have some basic knowledge of some things work but nothing about radio frequencys. would this light up or react to a cell phones rf? or something such as WiFi? I'm trying to make something that will light up or react when my cellphone goes off or I receive a text.
suilenrock11 months ago
Thanks for this great post! Can't wait to do it myself on my next weekend project.
dspecht21 year ago
This is a nice tutorial but it would also be interessting to see how you connect your antenna to the mifare RFID Chip. Is there also a tutorial for? Thanks!
Hello,

I want to make UHF tag with 865 to 868 MHz . what you should i have to change in above material to make RFID tag?
Hi,

Nice RFID instructable! I have a project in mind for an RFID reader, I have a specific requirement for the antenna's placement and wondered what I need to take into consideration. What materials are suitable power requirements number of loops etc etc. Are you able to help me?

Thanks
ScottSEA3 years ago
You should change "stripes" to "strips"... otherwise, a very nice instructible.
"Instructable"
Who cares.
DoctorDv2 years ago
I am new to electronics and RFID, but how does the LED get the power to light up? Thanks for the great post!
Magic.

In this particular instance, it takes the form of a series of ripples in the fabric of the universe that can propagate across space. This form of magic is commonly referred to as an 'electromagnetic field'. The RFID reader creates an electromagnetic field nearby it that induces (induction is the process through which a changing electromagnetic field creates voltage across metal objects) a voltage (a term used to refer to the total difference in the amount of positive and negative magical energy between points) along the length of the antenna. The LED then allows the positive and negative magical energies on either side of it to pass through it, annihilating each other in the middle, and creating another type of magical ripple (commonly called electromagnetic radiation) that you observe as light..

That is also the same reason that metal sparks when you put it in the microwave (I have personal experience doing this...), because the microwaves induce a (pretty high) voltage across the metal, enough to make sparks jump.
Wow! Thanks!

-Doctordv
I used some of the information here to successfully design and create a RFID Reader Detector that operates at a very low standard frequency, 125 kHz. SparkFun and others sell devices that operate at 125 kHz.
Because of this much lower frequency, my antenna coil and capacitor have much large values that the device described here. My Instructable also includes the math that underlies the selection of coil and capacitor sizes. You can find more about this if you can successfully go to
http://www.instructables.com/id/RFID-Reader-Detector-Easy-to-Build/.
Also, it is important to remember that a RFID Reader is a completely different device than a RFID Reader DECTECTOR. My device merely lights up if it is close enough to a Reader that is using/emitting a 125 kHz signal...
This is a fascinating project. I've been looking for a way to build a (very) cheap RFID reader, and I was wondering, have you tested this as an aerial for a reader?
oshe2 years ago
i would like to know about the RFID reader if it is universal..
or it can read any tag...

this is so nice...it really helps...

thank you..
francisroan2 years ago
do you know how to make an rfid "reader"?
Maknum2 years ago
Can you make the antenna as big as anyone would want it to be? For example: half a metre? I am making an gramophone-like player for kids. Where they can place cubes that represent different tones on the "installation". But all RFID antenna's that are for sale are to small for the radius.

DoctorDv2 years ago
You should enter this in the kit challenge.
-Doctordv
jnandakumar2 years ago
Please tell me why the tilt switches are required?
Can you please tell me the dimensions of the antenna you have made along with the spacing between two loops?

Thanks!
yaly2 years ago
can i use nickel tape instead of copper?
Would it be possible to use clear nail polish, instead of the insulating tape, to cover the the antenna loop where the antenna lead crosses?

Also, would it b epossible to use a "zig-zag" or "back and forth" pattern instead? This way it would be to possible prevent the crossings in the first place.
kgee2 years ago
Nate Marquardt? lol
pentagon1233 years ago
Cool :)
i8055 years ago
i very much enjoyed this inscrutable and very educated too. would it possible to use a thin copper wire(0.1-0.5 mm) i pulled out of a small mooter ? from my understanding if i were to be near a shop with RF reader(those that prevent stealing)will it light?
nmarquardt (author)  i8055 years ago
Yes, this is absolutely possible. You can use thin copper wire for the antenna; in fact, most commercially available RFID tags use this material for their small integrated antennas. I've added a small image that shows such a tag and the thin wire of the antenna. However, if you create such an antenna by yourself, you have to do a few experiments with the length of the antenna wire as well as the number of loops. About your second question: you're right, a few of the security systems in stores use the 13.56 MHz RFID technology, so the LED of our simple detector would light up (I tested it :). However, quite many stores use different (sometimes proprietary) technology, that also uses a different frequency and protocols. In this case, the detector in its current form would not work, but you can modify the design (antenna, capacitor) to work with different RFID hardware and frequencies.
RFID-wire-antenna.jpg
i805 nmarquardt5 years ago
thanks if you say I'll have to try different lengths and loops than i give up cause i don't think it will be appropriate doing this near the RFID reader in the shop. another Q if the led will light will the RFID reader will beep too(in the shop)?
nmarquardt (author)  i8055 years ago
No, these simple RFID detectors (via inductive coupling) are usually invisible for the RFID readers in shops. Furthermore, the RFID readers for security in shops usually respond to a specific signature on the chips. However, sometimes they are tuned very badly, which means they give a lot of false alarms, and then they might also give alarm when only this simple circuit is near the RFID reader. In all cases where I tested it, the security RFID readers in shops never gave alarm.
i805 nmarquardt5 years ago
thanks i went down the mall to a clothing shop and saw a rectangular plastic attached to a clothe,only the cashier can separate it with a sort of a device, do you know what is the technology of the this(-the separation- i know there is RFID chip inside the plastic). for education purpose only .
larryd2241 i8053 years ago
There is a magnet in the device that releases the little fingers in the tag
nmarquardt (author)  i8055 years ago
I know what you mean, but to be honest: I don't know how this mechanism works. As you mentioned, the 'security' part of this inside works with RFID technology as well. But for the 'separation' part of this, I have no idea of how it is implemented (and I'm sure the company that is producing these security parts is happy about keeping their secret :-). I could imagine it is some kind of a special electromagnetic field that is releasing the security tag (with a specific pulse pattern?). But this is just a guess; maybe someone else has an idea of how this could work.
i805 nmarquardt5 years ago
thanks anyway for your kindness and taking the time for answering :)
el greeno i8055 years ago
I believe its just a magnetic catch, which can be seperated using a strong magnet. I saw it on a police programme in the UK where they caught a shoplifter with a massive magnet in his pocket.
there are some rfid stickers which have just 3 different shaped metal sheets laying on each other, how do they work?
cooldog5 years ago
if you add more conductive boxes to the RFID tag reader will i work at farther ranges
nmarquardt (author)  cooldog5 years ago
Adding more loops to the antenna does unfortunately not directly improve the detection distance. Instead, it is important to optimize the tag for resonance to the 13.56 MHz frequency of the reader. There are two very important parameters for optimization: the length and number of antenna loops, and the parallel capacitor (parameters with smaller influence are for instance the material of the antenna, the form of the antenna, as well as the thickness of the material). Three to four antenna loops are very good for the material we proposed (copper tape) as well as the 82 pF capacitor. For optimization, a trim capacitor (e.g., 10 - 140 pF) could be used, in order that you then can "tune" the capacitor to optimize the detection distance. The most important factor is actually the RFID reader itself (e.g., the strength of the EM field), so it is good to do experiments with various RFID readers. In our experiments the maximum detection distance (with the small Sonmicro RFID reader we mentioned) was around 20 cm. There is a theoretical maximum reading distance for this class of RFID readers (near-field) of around 1.5 meters. There is, however, the ultra-high frequency (UHF) technology of RFID that allows a reading distance of tags of more than 10 m. This RFID hardware is more expensive and also more difficult to set up. But the ideas explained in this Instructable (detection, tilt-sensitive) can be used with the UHF RFID systems as well.
To improve the signal quality, wouldnt it be better to use a different metal such as steel or aluminum? Or, in this case, would that be unnessacary?
For the antenna, is there any place other than on the internet where copper tape is readilly available?
static dagenius3 years ago
Alternately you could etch the antenna, and circuity on a PC board using materials readily available from Radio Shack.
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