Good plan. Look for a checksum, though, to channel Captain Obvious. Likely they will use some common algorithm, programmers are lazy and either homebrew it simple or use libraries.
I did some minor poking around the Dublin bus cards, the disposable paper ones. Got a stock of them, to be used as generic NFC tags; just associate a serial number to action. Anything that can be read will do the job in this way.
Or make the “cartridge” read-only so it won’t decrement the remaining filament value.
But if you can generate the cartridge ID randomly, you won. Just feed the emulator from the printer and make a new value at each power-on. We did something similar with an emulator of phone calling cards, the EPROM-based ones.
Try this for the card emulation:
http://open-nfc.org/wp/home/features/
I think some Android phones can emulate the NFC cards too.
And if it is a 125 kHz RFID, there should be some Microchip PIC assembler code for read-only tags. (Or maybe ATtiny or so?)
