[Nicholas] built a simple NFC tag using an ATtiny84 microcontroller, four resistors, three capacitors, a diode, and an antenna. It implements ISO 14443-3, a standard for identification cards, and can communicate with the NFC chip sets found in most new smartphones.

This standard uses on-off keying for communication, which makes the hardware slightly more complex than the AVR RFID tag that we saw a few years back. The antenna and a variable capacitor form an LC circuit tuned at 13.56 MHz, which is the carrier frequency for the protocol. The diode acts as an envelope detector, letting the microcontroller recover the signal.

It may not be fully compliant with the standard, but [Nicolas] successfully tested out the device with his Lumia 620 phone. The firmware is available on Google Code so you can program your own tag data into main.c, build the firmware, and send some NFC packets. You can also check out a demo of the device after the break.

8 thoughts on “A DIY NFC Tag

  1. This should probably be called DIY NFC reader. NFC tags are passive. Where as this is more like what you’d find in a smart phone itself. Either way it’s pretty cool, I think I’ll build one and i’d like to see his code stay as in-line with standards as possible.

    1. It’s correct to refer to this as a tag: It’s passive (meaning it doesn’t generate a field to send data) and implementing the PICC side of the conversation. However, it’s *not* passively powered from the field, and also independently clocked (his writeup mentions problems matching the µC clock to the carrier clock), so it’s more of a tag emulator than a fully passive tag. The original inspiration Nicholas links to, http://scanlime.org/2008/09/using-an-avr-as-an-rfid-tag/, is actually a fully passively powered and clocked tag.

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