I find the ID12 device ideal for most projects. It can be linked up with just some jumpers on the back of the ID12 and treat it as a "Three Wire Device"
Bring back three wires to the PICAXE / proto board... +ve, -ve and it just spits out a unique 12 ASCII character 9600 baud sequence when ever a FOB comes within range. The standard tags are NZ$5 each and come as a FOB or key ring but flat cards and or cattle ear tags are becoming available.
I have set up an over clocked 5% detuned 08M to read the 12 x 9600bd ASCII digits sent out by the ID12 at 4800bd. This "halves" the number of digits but still works fine for student projects.
What the student wants to do with the 6 unique ASCII bytes is up to them. Some cards can be set up as "master" and allow hierarchical control of the logic in the program etc, time switches. I make the 6 digits play a tune so you can “hear” your own unique code as you log in.
http://picaxe08.orcon.net.nz//Photos/PICAXE/Proto/Data/RFID.jpg
http://picaxe08.orcon.net.nz//Photos/PICAXE/Proto/Data/RFID-sch.jpg
- Andrew