i mean, the real things are only about $2 and an attiny chip is $1, and your time is surely worth something, and you should just get a numeric code to get into sudoroom, which doesn't require any matter, but in case you decide to make an RFID tag yourself, here's how: http://scanlime.org/2008/09/using-an-avr-as-an-rfid-tag/ i believe this will work with the sudoroom RFID reader. but why bother? you can just buy a tag or get a code you can type in. -jake