I’d like to put the NFC reader away from the tablet, should I go the arduino board or iButton and if iButton, what reader should I purchase?
I use iButtons as they are durable, all my friends can easily keep them on their keychain so they always have it with them, they are cheap to replace if lost and very easy to associate with a user in the tablet app (simply put an ibutton on the reader and the tablet will prompt you to click a username to associate it with).
Mike is working on a firmware update for the KBPM at the moment which will allow the ibutton to trigger a relay so you can activate relays with it meaning no-one can pour a drop without authenticating (if you add the solenoid valves of course - I already have them in my system and am just waiting for the firmware update). Mike said a couple of weeks ago the update would be ready in a week or two so it should be available any day now.
As for the reader, the one I use (which works great) was $20 and works well: http://www.embeddeddatasystems.com/DS1402D-DR8--Blue-Dot-Receptor-iButton-Reader-Cable_p_88.html
The same website also sells ibuttons but they are about $3 each from them. I bought a few of theirs to setup my system with and make sure everything works but have since found the ibuttons on ebay you can buy work just fine. I paid $42 for 100 on ebay and they came already with the keyring mount.