RFID sniffer

RFID sniffer

About this project

RFID is everywhere. Use the easy to build RFID sniffer to find out if objects are tagged.
The RFID sniffer is a simple analog electronic circuit which can detect the presence of 13.56 MHz RFID tags. These tags are commonly used in all kinds of plastic cards like access badges, bank cards, library cards, loyalty cards and so on. Also many other objects may carry RFID tags without you knowing it. Books, toys, and even clothing might be tagged. Carrying tagged objects with you can reveal your identity or whereabouts to anyone equipped with the appropiate tools to read RFID tags.
The RFID sniffer helps you identify which objects are tagged, and which are not.

Prototype

RFID snifferPosted by marc 2007-11-11 18:18
I assembled the first prototype of the RFID sniffer on one of the printed circuit boards. Soldering the small SMD parts requires a good soldering iron with a fine tip, a pair of tweezers and a steady hand. I first tinned all solder pads and removed excess tin with the help of solder wick. This makes soldering the parts much easier.
Then I placed the SMD parts one by one, holding them with the tweezers and heating one of the solder pads to fix it in place. Then applying a little bit of solder to each of the other pads. Again using solder wick to remove excess solder if needed.
The trimmer and potentiometer were the hardest parts so solder, due to the small contact surfaces on these tiny components.

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After connecting the battery, I pressed the switch and the LED came on. I just had to adjust the level of the potentiometer to set the threshold to light the LED only when a RFID tag is near the loop antenna.
Measuring the frequency with an oscilloscope revealed that the frequency was about 16 MHz, quite a bit higher than 13.56 MHz, but it could still detect tags. I adjusted the trimmer capacitor anyway, to set the frequency to approximately 13.56 MHz.
The full range appeared to be from 12.7 to 16.2 MHz, but it hardly affects the detection of tags. I can probably get rid of the trimmer and use slightly higher values for capacitors C1 and C2 to fix the frequency to within a few percent of 13.56 MHz.

The oscillator frequency can be measured without having a oscilloscope probe making contact with the circuit. You can construct a coil from a few turns of solid copper wire and hook it up between the tip of the probe and its ground clip, and then holding it close to the loop antenna. This will pickup the emitted RF signal just like a tag would do.

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