http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Home   Sign Up!   Explore   Community   Submit

RFID Reader Detector and Tilt-Sensitive RFID Tagby nmarquardt on October 30, 2008

Table of Contents

intro:   RFID Reader Detector and Tilt-Sensitive RFID Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

step 1:   Material and Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

step 2:   Building the RFID Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

step 3:   RFID Reader Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

step 4:   Tilt-Sensitive RFID Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

step 5:   Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Advertisements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Customized Instructable T-shirts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

intro:  RFID Reader Detector and Tilt-Sensitive RFID TagThe '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, andsome readily available electronics hardware.

Longer preambleRadio frequency identification ( RFID) is rapidly growing in popularity. RFID tags are found everywhere. They're attached to container freight, in those funny-looking whitelabels 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 IDnumber, 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 tobe 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 supplychain. 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-moneypayments 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 interactionwith 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 workingsof 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 tosupport some interesting interactions. We offer some other possibilities that build on our examples at the end.

Image Notes1. Tilt-sensitive RFID tag

Image Notes1. Simple RFID reader detector

Image Notes1. Tilt-sensitive RFID tag2. RFID reader detector

Image Notes1. Small RFID stickers2. RFID tag in the form of a credit card3. Inside of RFID tags: antenna and connected chip

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

step 1: Material and ToolsThis 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)

Image Notes1. Conductive copper tape2. Capacitors (e.g., SMD) 82pF3. Cardboard, around 100x70 mm4. LED (light-emitting diode)

Image Notes1. Insulation tape

Image Notes1. Antenna of the Sonmicro RFID reader2. Sonmicro 13.56 MHz RFID Module

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Image Notes1. Micro tilt switches2. RFID ICs (MIFARE Standard 1k)

step 2: Building the RFID AntennaThis step describes how to build the antenna for the RFID tag.

Building the RFID tag antennaTo 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 theantenna.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 youwant 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 backgroundRFID 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 istransmitted 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 readerto induce current to the antenna of the tag.

Image Notes1. Thin stripes of the conductive copper tape (around 2 mm thick)

Image Notes1. Taping the copper stripes onto the cardboard

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Image Notes1. Three loops of the antenna

Image Notes1. Soldering the copper tape connections2. Soldering the copper tape connections

step 3: RFID Reader DetectionThis step describes how to add a simple mechanism to the RFID tag antenna that allows us detect nearby RFID readers.

Antenna connectionFirst, 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. Thenwe 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 LEDNext, 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 thecopper tape (see Figure 4).

TestingWith 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 LEDlights 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 andtherefore 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.

Image Notes1. Adding insulation tape for the connection

Image Notes1. Adding connection to the inner end of the antenna loops2. Soldering connection again

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Image Notes1. 82pF Capacitor2. Low current LED

Image Notes1. Soldering connections2. Soldering connections

Image Notes1. RFID reader is near the tag2. LED lights up

step 4: Tilt-Sensitive RFID TagWe now describe the process of how to build a tilt-sensitive RFID tag. This extends the previous exercise.

AntennaThe 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 2of this instructable.

Tilt-sensitive tagNext, 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 tothe 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 statewhile 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 alternativeoptions).

Testing the tilt-sensitive tagWe 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 inactivewhen in a vertical position as in Figure 6.

Using RFID chipsWe 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 nolonger visible through the LED, but our tag is then readable by the RFID reader and responds with the unique ID number of the chip.

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Image Notes1. Additional copper tape for connecting the tilt switches, the capacitor, and theLED with the antenna.

Image Notes1. Again we use insulation tape for the connection2. Soldering all copper tape connections

Image Notes1. SMD capacitor (82 pF)2. Again a connected low current LED3. This arrangement of the tilt sensors makes is possible to sense the horizontal orvertical position of the tag.

Image Notes1. The angle of the tilt sensors is important

Image Notes1. The tag is activated when it is in a horizontal position

Image Notes1. As long as the tag is in a vertical position, the tag is inactive

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Image Notes1. Using the MIFARE RFID chips to create a tilt-sensitive RFID tag

step 5: VariationsThis 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!

Image Notes1. Variable length (and loops) of the antenna2. Switch to activate and deactivate the RFID IC

Image Notes1. Experiments with form factors for the RFID tags

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Image Notes1. Button to switch between LED reader detection and the RFID tag2. RFID chip MIFARE 1k

Image Notes1. Light sensitive tag

Image Notes1. Capacitive touch-sensitive pad2. Voltage regulator3. Diode

Image Notes1. Antenna layout painted with conductive silver ink.

Image Notes1. This antenna layout is stamped with conductive silver ink (and the antenna is infact working!)

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Related Instructables

RFID ProofSoda Can Walletbyprometheus442

How toblock/kill RFIDchips byw1n5t0n

RFID SecureWallet bydogsrcool2me

How to make aRFID pet foodaccess controlsystem bymlarsen

AccelerometerTilt ControlledWireless RGBLED-lights(video) by Andlier

RFID ShieldingPouch Out of'Trash' by laras

Low Cost WaterFlow Sensorand AmbientDisplay bystaceyk

How to makesimple "motion"sensors byteebee918

AdvertisementsCustomized Instructable T-shirts

Comments50 comments Add Comment view all 51 comments

 Openyourmind says:  Dec 21, 2008. 12:52 AM  REPLYHello,first of all, I would like to say that I know absolutely nothing about electronics, and, of course, RFID... So it seemed impossible to me, at first glance, that itwould work !Then I decided to have a try. I went down to my local electronic stuff supplier, bought all the required components and built a sample...What was my surprise to find out that it actually works !So I would like to thank you for your GREAT Instructable. Very well explained and documented.

Now, here are some questions...

How are "stored" the informations into the tag and how is it possible to modify (interact with) them ? You say that The technology is also used in mass transitsystems in cities like London and Hong Kong. In Japan, many mobile phones incorporate readers to enable e-money payments in shops and vendingmachines.Do they need a distinct "writer" and a distinct "reader" ? How come the reader can not also write ?

If a Faraday cage would "shield" the tag from the reader, why shoplifters don't simply coat the tags with some metal (aluminium foil) ?

What if I put two (or several) tags close to each others ? Will the reader get confused ?

Finally, are you some kind of electronic engineer/teacher ?

I am looking forward for more Instructables from you !

Thanks again.

 nmarquardt says:  Dec 21, 2008. 12:46 PM  REPLYHello! Thank you very much for your feedback; I'm glad that your custom RFID tag/detector that you've built worked :-) I will try to answer all yourquestions:

@reader/writer: the reader hardware for this 13.56 MHz RFID standard can usually read and write. You can connect these readers to you computer, andby using a special software you can then read the ID numbers of the tags, and also write small data packages onto the tags (between 200 and 3000byte; sometimes a bit more, depending on the tag hardware you use - I mainly use the Phillips MIFARE tags). Some RFID readers that you can buy canonly read and not write new data to the tags. I'm sorry, but there is no easy answer to this question; there exists far too many different RFID hardware. Ifyou have questions about a particular RFID hardware you can of course send me a message. By the way, all this information is only for the 13.56 HFRFID standard; but there are many other standards available (125 kHz or the UHF standards).

@faraday: depending on the thickness and material of the metal shield this would work in general. but the security tags in shops use many differentfrequencies, stronger EM fields, and also sometimes active tags (i.e., with a battery inside). I assume aluminium foil would not work; maybe other metalshields. Maybe it is good that we don't know for sure how this works ;-)

@multiple tags: yes, you're right, they interfere with each other. Therefore, usually the RFID readers can only detect one tag at a time. More advancedhardware (with included "anti collision detection") can detect multiple tags at the same time; they cycle through frequency variations and protocols toaddress different tags at the same time. There is unfortunately not much information available about this anti collision detection for RFID.

@teaching: interesting question :-) I'm not a teacher for electronic engineering. I'm currently a PhD student (originally from Germany, now studying in

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

Canada), and worked with RFID technology in a side project of my PhD and during an industry internship. I continue this research at the moment, and Iwill try to create a few more instructables about it in the next months.

 Openyourmind says:  Dec 24, 2008. 1:27 AM  REPLYThank you for your reply...

Here is the picture of the RFID detector I built. It lies over a mass transit system card. I tried to bring both card at the same time from the reader, andthe bip was much louder than usual and the LED fully lit up (normally it flashes) !I also tried with my cellphone in the same hand, and it acts like a shield so the LED didn't lit.Then, I carefully pay attention to the reader during the rush hour. People were swiping their card all at the same time, but the reader didn't seem toget lost...

Can I compare the MIFARE you are talking about to some kind of (computer) ROM ?

And BTW, you are right about not getting too much infos about the Faraday process !

I am fascinated by this technology. Thank one more time for your Instructable and your many answers. :-)

 nmarquardt says:  Dec 28, 2008. 9:49 PM  REPLYIt's great for me to see your custom built RFID reader detector! I'm glad the instructions worked for you!@cellphone: interesting that the cellphone transponder interfered with the RFID; I didn't noticed such an effect yet.@reader-during-rush-hour: yes, these readers can detect many cards at the same time, and read/write information from/to these cards. However,I don't know the specific properties/characteristics of the hardware they use.@mifare-storage: yes, you could compare it to the flash memory (as for instance in USB thumbdrives). With the adequate hardware and softwareyou can read and write the memory cells of the chip, to store custom information on it. This works very fast; it is enough to swipe the card overthe reader for milliseconds. I used this in experiments to store keywords, URL, and other data on the RFID tags. The MIFARE ICs only store afew bytes, but there are other RFID ICs that can even store mega bytes of data.

 jhalex_012 says:  Dec 21, 2008. 2:08 AM  REPLYi would like to ask how many of this custom tag can be recognize by a compatible reader? is there any limit?..hope for your quick response thanks..

 nmarquardt says:  Dec 21, 2008. 10:52 AM  REPLYUsually, the RFID readers can only detect one tag at a time. There are, however, more advanced readers that can detect multiple tags at the same time;the keyword to look for is "anti collision" RFID reader. But they are definitely much more expensive than the RFID reader hardware mentioned in thisarticle (or in the comments below).

 jhalex_012 says:  Dec 22, 2008. 5:53 PM  REPLY

thanks for answering my query! -

 i805 says:  Nov 18, 2008. 11:02 AM  REPLYi 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 says:  Nov 18, 2008. 11:57 AM  REPLYYes, this is absolutely possible. You can use thin copper wire for the antenna; in fact, most commercially available RFID tags use this material for theirsmall 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 byyourself, 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 detectorwould light up (I tested it :). However, quite many stores use different (sometimes proprietary) technology, that also uses a different frequency andprotocols. In this case, the detector in its current form would not work, but you can modify the design (antenna, capacitor) to work with different RFIDhardware and frequencies.

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

 zimmemic25 says:  Nov 29, 2008. 1:54 AM  REPLYthere are some rfid stickers which have just 3 different shaped metal sheets laying on each other, how do they work?

 i805 says:  Nov 22, 2008. 11:38 AM  REPLYthanksif 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 says:  Nov 22, 2008. 2:06 PM  REPLYNo, these simple RFID detectors (via inductive coupling) are usually invisible for the RFID readers in shops. Furthermore, the RFID readers forsecurity in shops usually respond to a specific signature on the chips. However, sometimes they are tuned very badly, which means they give alot 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, thesecurity RFID readers in shops never gave alarm.

 i805 says:  Nov 28, 2008. 8:48 AM  REPLYthanks

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 adevice, 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 .

 nmarquardt says:  Nov 28, 2008. 9:15 AM  REPLYI know what you mean, but to be honest: I don't know how this mechanism works. As you mentioned, the 'security' part of this insideworks 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 thecompany that is producing these security parts is happy about keeping their secret :-). I could imagine it is some kind of a specialelectromagnetic field that is releasing the security tag (with a specific pulse pattern?). But this is just a guess; maybe someone else hasan idea of how this could work.

 i805 says:  Nov 29, 2008. 11:50 AM  REPLYthanks anyway for your kindness and taking the time for answering :)

 zimmemic25 says:  Nov 29, 2008. 1:52 AM  REPLYhow much power is usable for the led?

if its more than 1V, i could add a piezo beeper.

and btw. is it ac or dc? cause the beepers i use only work on dc.

 leahbuechley says:  Nov 26, 2008. 5:02 AM  REPLYvery cool instructable! Great detail and pictures! Out of curiosity, have you ever built any of these circuits on flexible substrates -- fabric or paper forexample?

 nmarquardt says:  Nov 28, 2008. 9:20 AM  REPLYHi, thank you for your feedback! Yes, I have also a few examples on flexible material. Paper works good with the conductive tape on it; and if you use aconductive pen to paint the antenna, you just have to make sure to not bend the paper too much, as it could remove the silver particles from the paper(and you then loose the connection).For fabric: yes, I tried this as well. First, using thin wires on normal fabric, and second, using conductive fabric (very expensive). Both works great, andthis is definitely the fun part of this project: trying out all different kind of materials, simple sensors, and combinations of them.

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

 aballen says:  Nov 19, 2008. 8:44 PM  REPLYThis is a great article on inductive coupling. I see how to power an led via inductive coupling, and then switch it with the rfid tag, how do I read the id on thetag?

 nmarquardt says:  Nov 19, 2008. 11:15 PM  REPLYTo read the ID on the tag, you actually need to use one of the mentioned RFID readers, and either use the communication protocol for this reader (e.g.,serial protocols), or you use the often included software tools and SDKs. You can then read the tag ID, and also write custom data to tags (if the tagssupport this, as for instance the MIFARE 1k, 4k, ultralight).

 k-twizel says:  Nov 19, 2008. 7:51 AM  REPLYJust wondering if anyone knows how to program a RFID with a custom ID... thinking about an RFID blocking purse/wallet that has a 'honey pot' tag on theoutside with a custom message like "Byte Me" or "Hands up, Sucka!"

 nmarquardt says:  Nov 19, 2008. 11:12 PM  REPLYThere are many RFID readers available that let you write data onto the tags; for instance the mentioned Sonmicro RFID reader (but many others arementioned in the comments here). With their provided software tools you can write data (around 600 bytes and more) to the tag. However, if all the otherRFID readers will then access this data is maybe not always the case, as they use proprietary protocols.

 msweston says:  Nov 11, 2008. 12:25 PM  REPLYThis is really cool. I like the idea of being able to paint electronics :-)

I think I might just have to try this over thanksgiving break!

 nmarquardt says:  Nov 11, 2008. 2:42 PM  REPLYYes, the painting of the tag circuits is really interesting. Btw, you can find "conductive pens" (e.g., on ebay) that make it very easy to paint/draw theantenna loops and any circuit connections.We look forward to hearing from you when you tried it out. Just write a message if you have any further questions.

 msweston says:  Nov 14, 2008. 6:36 PM  REPLYI tried a simple version of this just the other day, I used a silver "micro-chip repair pen" and it was very interesting! There was some resistance (only afew Ohms though) but it could easily light up an LED. Can't wait to try this with the chip and all too.

~P.S. For anyone else printing their circuit be sure to give some thickness to the antenna, for some reason there is a drastic difference in the signal itpicks up with a thinner antenna.

 rblee says:  Nov 12, 2008. 10:08 AM  REPLYI don't suppose anyone does inkjet cartridges with conductive ink in them do they? How cool would that be?

Thanks for the instructible BTW, there's a lot of really good ideas in there.

 11010010110 says:  Nov 12, 2008. 12:09 PM  REPLYis there a standard inkjet ink that makes thick layer ? if yes it can be used to create a negative and then painted over and wiped out

 nmarquardt says:  Nov 12, 2008. 11:27 AM  REPLYOh yes, this would be great! There are already PCB printing machines (or advanced 3D printers) that can do this; but unfortunately their pricegoes far beyond the usual Instructable budget :-)But it would be great to have a cheaper way to print with conductive ink. For anyone trying this out: the tricky part of this is that the conductive inkis viscous (mainly because of the silver particles). But maybe someone finds a way to work around this. The ink definitely works well for paintingand stamping...

 srhadaham says:  Nov 12, 2008. 10:32 AM  REPLYthat would make life a lot easier for those of us with limited soldering skills

 luketanti says:  Nov 14, 2008. 11:05 AM  REPLYHello. what is the power source for the led?? Or does it get free energy?

 nmarquardt says:  Nov 14, 2008. 12:43 PM  REPLYThe current is induced by the RFID reader to the antenna of the tag (inductive coupling). There is no battery or other power source necessary (butpossible -> active RFID tags). You can find more information about this by searching for "inductive coupling" (e.g.,http://en.wikipedia.org/wiki/Inductive_coupling), "parasitic power" as well as "resonance circuit".

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

 static says:  Nov 12, 2008. 9:31 AM  REPLYThis device is mostly for detecting the presence of RFID readers, right? Wouldn't a conventional radio receiver, that activated a surplus cell phone vibrator,be constructed smaller, and give an alert without watching an LED? Not to mention a better range(distance) of detection?

 nmarquardt says:  Nov 12, 2008. 10:59 PM  REPLYYes, you're right, it would have a better range for the detection. However, designing such a circuit goes beyond the very simple principles of this article.I actually designed such a circuit with a custom PCB and it's own energy source; and I hope to find the time to write an article about it and share this withyou. The detection distance goes far beyond the passive detector (up to 45 cm), but it is still quite complicated to build this in a very small form factor(antenna, battery). I would be happy to hear more about your suggestions for this.For me, the focus in my experiments was actually not the "RFID detection" itself, but working on experiments of how to change and modify the usualbehaviour of the RFID tags.

 solis365 says:  Nov 14, 2008. 5:12 AM  REPLYthe antenna material, being copper tape, is moderately flexible. you could install this circuit with a vibrator/buzzer/light into a backpack or purse. thiswould give enough room to stow a small battery pack (like the size of a few AAs) and make an active detector. I could also imagine making a fabric"patch" that can be stuck inside a shirt sleeve, etc.

I would like to hear more about this active device youve created... another instructable perhaps?

could also add a switch that controlled an array of filters. switch between filters and youll be able to look for multiple different kinds of RFID (i.e.,different frequencies)

 Photo-Worx says:  Nov 13, 2008. 12:29 PM  REPLYAnother place to get an RFID reader and tags starter kit is at Parallax. This kit only costs $45.99 and will work with a microcontroller or a pc. Comes with avariety of tags too.

 11010010110 says:  Nov 12, 2008. 12:14 PM  REPLYif you put a transistor instead of just LED you can amplify it to boost sensitivity and to power something else except a low current led

 nmarquardt says:  Nov 12, 2008. 4:33 PM  REPLYThat is a very good point, thanks for your comment. A transistor before the LED is definitely very useful for optimizing the detection. Powering somethingelse (besides the LED) is however still challenging (without switching to active tags).

 11010010110 says:  Nov 13, 2008. 8:59 AM  REPLYwhy not active tag ?

you dont need much energy anyway so maybe precharged capacitor is enough

you can also use tiny solar cell

 tewfik says:  Nov 12, 2008. 8:28 AM  REPLYThank you for this great Instructable !

I enjoyed reading it, well documented and step by step, it was a pleasure to learn how to build a rfid detector

also i think it lacks (imho) a bit of 'black magic', like how did you simulate the behaviour of the antenna ( what kind of software) , what knowledge is requiredto do this kind of stuff ( works the first time, needs tuning ) , or if it is possible to glue some CMOS logic ( or something analog) to the antenna to reproducean rfid response.

thanks again,

cheers

 nmarquardt says:  Nov 12, 2008. 9:54 AM  REPLYThanks for the feedback: these are great ideas for a follow-up article :) We really tried to keep this first article as simple as possible, so that even peoplethat are not familiar with electronics, RFID, etc. can start doing simple experiments.But here a few initial thoughts to your suggestions:simulate behaviour of the antenna: there are two sides of software (for the reader and of the tag IC). The mentioned Sonmicro reader provides a set ofdevelopment tools, libraries, etc. On the side of the RFID IC, we used Mifare 1k, 4k, and a few others. While we did more experiments with reading andwriting of these tags, we did not yet develop custom ICs for RFID.necessary knowledge: so far I've built around 25 of various custom RFID tags, with different antenna layouts, used materials, tuning capacitors, andintegrated sensors (and not everything of this worked :-). It also included much more experiments with various RFID readers, frequency generators, orcustom software tools. While this Instructable should be very easy to understand, there is definitely potential for many further experiments with thisapproach. And to your last question: this is absolutely possible, and I'm working on these things at the moment. There also already exist other projectsrelated to that, for instance the OpenPICC (http://www.openpcd.org/openpicc.0.html). If you have skills of how to build PCBs you will be definitely happywith this project :-)

http://www.instructables.com/id/RFID_Reader_Detector_and_Tilt_Sensitive_RFID_Tag/

 rblee says:  Nov 12, 2008. 4:07 AM  REPLYRFID readers are usually quite (and unjustifiably!) expensive - The one mentioned in this instructible is nearly $150 for the USB version.

Take a look at http://tikitag.com

They do a starter kit of tags and reader for about $50. It looks a bit proprietary, but it does work at 13.56MHz, and reading s/w is available for Windows,MacOS and Linux (Debian/Gnome only, as far as I can tell).

The reader must be detecting all 13.56MHz chips, although possibly filtering non-Tikitags out, so it may just be a software problem.

Be warned though - The reader's firmware is held on a smartcard, reputedly to keep the cost down, so if the filtering is done in the reader itself this mighttake a LOT of work to hack.

So what else are you going to do now winter's here? :)

 nmarquardt says:  Nov 12, 2008. 9:26 AM  REPLYThank you for this suggestion. This RFID starter kit looks like a great starting point for experiments with RFID. The basic 'detection' of this reader with ourdetector-tag should would work right away (because they use the same frequency). If you want to build custom RFID tags for this, you could also thinkabout trying to use one of their special tags, remove parts of the tag to find contacts to the chip, and then add the tilt switches or any other sensors to it.Otherwise, they also write in their FAQ that they also consider opening their service for other tags, and users that are interested in that should send theman email. Besides that: your idea of working around a software filter on the firmware sounds also like an interesting hack :)

 Sparrowhawk says:  Nov 11, 2008. 4:27 PM  REPLYIt would be great to combine one of these detectors with a secure wallet.Not only is your data safe, but you're warned if someone tries to swipe it!

 nmarquardt says:  Nov 12, 2008. 9:06 AM  REPLYThis is a great idea! When building this you have to make sure to have enough distance between the metal of the secure wallet and the RFID detector.Any metal nearby the RFID tag antenna decreases the readability of this tag: this is of course important for the function of the secure wallet, but it alsomeans that the RFID detector does not work if too close to the metal film of the secure wallet.

 mspark400 says:  Nov 11, 2008. 7:35 PM  REPLYI have been waiting a very long time for an instructable like this. Very clear, great pics, and useful as well as simple information.Fav + 5/5Cheers,Mspark400

 benz_z says:  Nov 11, 2008. 2:57 PM  REPLYnice -ible, can rfid tags be read trough fariday cages ?

 nmarquardt says:  Nov 11, 2008. 3:28 PM  REPLYFaraday cages are in fact a very good 'shield' around RFID tags and prevents that tags inside of the Faraday cage are detected by the RFID reader. Thisprotection would be the same for the tags we've explained here, i.e., they are not detectable when they're inside of a Faraday cage. Btw, it is alreadysufficient to cover only part of an RFID antenna with metal to make it nearly impossible to read the tag with the RFID reader anymore.

 cooldog says:  Nov 11, 2008. 1:19 PM  REPLYif you add more conductive boxes to the RFID tag reader will i work at farther ranges

 nmarquardt says:  Nov 11, 2008. 3:24 PM  REPLYAdding more loops to the antenna does unfortunately not directly improve the detection distance. Instead, it is important to optimize the tag for resonanceto the 13.56 MHz frequency of the reader. There are two very important parameters for optimization: the length and number of antenna loops, and theparallel capacitor (parameters with smaller influence are for instance the material of the antenna, the form of the antenna, as well as the thickness of thematerial). 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 trimcapacitor (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 factoris 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 theoreticalmaximum reading distance for this class of RFID readers (near-field) of around 1.5 meters. There is, however, the ultra-high frequency (UHF) technologyof 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 ideasexplained in this Instructable (detection, tilt-sensitive) can be used with the UHF RFID systems as well.

 Bongmaster says:  Nov 11, 2008. 12:21 AM  REPLYthis is kool :)so i could make my bus card wallet light up with an led wen i use my card on the bus :D. i assume using a detector along side a rfid card wont have anyeffect on the card being read?

view all 51 comments