For something somewhat left of field, electronics enthusiast Beth has documented how to use an Atmel ATtiny85 microcontroller as an RFID card. Naturally it still needs a large coil, however this can fit within the dimensions of a typical RFID card:
The ATtiny is powered in a clever way. The current from the RFID reader device eventually causes a sine wave of a few volts through the coil, which is connected to the I/O pins. As that voltage exceeds the supply voltage, the excess is diverted to the supply rails via the clamping diodes on the I/O. Ingenious. To read about the design and download the source code, visit Beth's fascinating blog here.
To get started with your own home-brew RFID card, we have the ATtiny85 available for fast delivery along with the rest of our wide-ranging catalogue. And if you don't feel like making your own RFID card, we have those as well. And for more news, updates and items of interest.please follow us on twitter, Facebook and Google+