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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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Step 1: Material and Tools

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This section provides an overview of the necessary materials and tools.

Materials (see Figure 1):
We need the following material to built the basic RFID reader detector.
- Cardboard (around 100x70 mm)
- Conductive copper tape (e.g., order number 1218478 at www.farnell.com)
- Capacitor 82 pF (picofarad) (e.g., order number 1138852 at www.farnell.com)
- Low current LED (light-emitting diode) (e.g., order number 1003207at www.farnell.com)

Tools (see Figure 2 and 3):
- Craft knife and scissors
- Insulating tape (e.g., order number 1373979 at www.farnell.com)
- Soldering iron and solder

RFID reader for testing (see Figure 4):
To test our RFID tags we need an RFID reader that can operate at a frequency of 13.56 MHz.
There many readers for this widely used RFID standard, for instance the Sonmicro MIFARE USB reader (http://www.sonmicro.com/).
Note: The Phidget RFID reader does not work with the tags created in this project, as it uses a different frequency for communication with the tags (125 kHz).

Advanced material (see Figure 5):
The following material is necessary to build the second part of the project: the tilt-sensitive RFID tag.
- Micro tilt switches (e.g., www.digikey.com)
- RFID ICs (e.g., MIFARE Standard 1k, part no. 568-2219-1-ND at www.digikey.com)

Step 2: Building the RFID Antenna

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This step describes how to build the antenna for the RFID tag.

Building the RFID tag antenna
To build the tag's antenna follow these three steps.
1. Cut the conductive copper tape into thin stripes of around 2mm (see Figure 1).
2. Tape these stripes (see Figure 2) in loops around one half of the cardboard (see Figure 3 for the layout of the antenna). The tag should have between 3-4 loops for the antenna.
3. Solder all the connections between the copper tape. Sometimes, this isn't necessary as the tape's adhesive backing is conductive, but solder the connections if you want to be on the safe side.

Now we have created our RFID tag antenna, and we will add the "RFID reader detection" functionality in the following step.

A little background
RFID readers transmit an electromagnetic (EM) field with their reader antenna. This EM field induces a current in the antenna for all RFID tags within reading distance. This induced current activates the RFID chip that is connected to the tag's antenna. This chip then modulates a response (usually the unique ID number) that is transmitted back to the reader. The antenna of an RFID tag is usually a thin copper wire that is arranged in loops. The loops allow the emitted EM field of the RFID reader to induce current to the antenna of the tag.

Step 3: RFID Reader Detection

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This step describes how to add a simple mechanism to the RFID tag antenna that allows us detect nearby RFID readers.

Antenna connection
First, we add a small piece of insulation tape for the connection of the inner end of the antenna loop (as illustrated in Figure 1). This is to insulate the outer loops. Then we add another copper tape strip to the inner end of the antenna as shown in Figure 2. Here again we solder the two ends of the conductive copper tape together.

Capacitor and LED
Next, we add the capacitor (82 pF) and the low current LED to the tag as shown in Figure 3. They are connected in parallel. We also solder these two components to the copper tape (see Figure 4).

Testing
With these simple steps, our RFID reader detector is finished! By bringing our DIY RFID detector close to an RFID reader (as shown in Figure 5), the connected LED lights up. With the Sonmicro reader hardware the distance to the reader has to be below 8-10 cm; however, there are RFID readers available with a stronger EM field and therefore a higher maximum reading distance.

In the next step of the instructable we will show how to extend a basic RFID tag and make it tilt-sensitive.

Step 4: Tilt-Sensitive RFID Tag

We now describe the process of how to build a tilt-sensitive RFID tag. This extends the previous exercise.

Antenna
The antenna for this second RFID tag is similar to the first antenna we built. We thus need another piece of cardboard and to repeat the steps described earlier in STEP 2 of this instructable.

Tilt-sensitive tag
Next, we add additional copper tape connections to the tag, as shown in Figure 1. These connections allow us to connect three tilt switches, a capacitor, and the LED to the antenna. Again, all the connections of the copper tape are soldered together.
We add the three tilt switches to the tag as shown in Figure 3. The tilt switches are soldered to the copper tape, and it is important to connect them in a slight angle (around 5-10 degrees) as shown in Figure 4. This makes sure that the silt switches are in a closed state while the RFID tag is in a horizontal position, and in a open state while the tag is in a vertical position.
Again, we also add an LED and a capacitor to the antenna as shown in Figure 3 (we use a different form factor of the capacitor here just to illustrate the alternative options).

Testing the tilt-sensitive tag
We can now use our Sonmicro RFID reader again to test our new tilt-sensitive RFID tag. The tag is activate while in a horizontal position as in Figure 5, and is inactive when in a vertical position as in Figure 6.

Using RFID chips
We can now replace the connected capacitor and LED from our tag with an RFID chip (e.g., the MIFARE 1k shown in Figure 7). By doing this, the activity of our tag is no longer visible through the LED, but our tag is then readable by the RFID reader and responds with the unique ID number of the chip.

Step 5: Variations

This section concludes our instructable of how to build custom RFID tags. Here are a few additional tags to show the possible variations.

- Variable length of the tag antenna, and therefore also variable reading distance of the tag (Figure 1).
- Experiments with the tag size and material (Figure 2)
- Switching between the LED and an RFID chip (Figure 3)
- Light-sensitive tag: the tag is active in daylight, and inactive in darkness (Figure 4)
- Touch-sensitive: tag is active when someone touches the tag with a finger (Figure 5)
- Different material for antenna by using conductive silver ink (Figure 6)
- Stamped layout of an RFID tag antenna (Figure 7) that is in fact working!

Many other variations of RFID tags are feasible... Happy DIY!
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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!

are you a pet stealer?

Iron MikeH1 month ago

why do you want to disable RFID tag? to steal something not yours?

JohnA154 months ago

what is the process of data transmission from tag to reader.

is there any boud rate consideratiion??

beyondal8 months ago

How do you determine the loops?

beyondal8 months ago

How do you calculate the windings for the flat planar coils?

djjrb3139 months ago

I am new to RFID technology, but really enjoyed this! It is finally making some sense to me. I am going to try to do this project on my own, but one of the materials you listed does not seem to be still at the same product number as before. As I said, I am new to this and don't know the difference between the other products available when I search for similar ones. Could you provide a link that would replace or is the same product as this material:

Capacitor 82 pF (picofarad) (e.g., order number 1138852 at www.farnell.com)

Thanks!

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mx281 year 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.
suilenrock1 year ago
Thanks for this great post! Can't wait to do it myself on my next weekend project.
dspecht22 years 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
ScottSEA4 years ago
You should change "stripes" to "strips"... otherwise, a very nice instructible.
"Instructable"
Who cares.
DoctorDv3 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?
oshe3 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..
francisroan3 years ago
do you know how to make an rfid "reader"?
Maknum3 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.

DoctorDv3 years ago
You should enter this in the kit challenge.
-Doctordv
jnandakumar3 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!
yaly3 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.
kgee3 years ago
Nate Marquardt? lol
pentagon1234 years ago
Cool :)
i8056 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)  i8056 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.
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i805 nmarquardt6 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)  i8056 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 nmarquardt6 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 i8054 years ago
There is a magnet in the device that releases the little fingers in the tag
nmarquardt (author)  i8056 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.
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