I just received my RC522 RFID reader and made this simple Arduino access control system that uses the reader, a buzzer for the alarm and a relay shield for the security system. The relay can be used ...

A second Arduino is used to read NFC and RFID cards using a Mifare RC522 reader. The system uses its own credit system, so a user can be issued a card with a certain amount of pre-paid credit.

If you're on the hunt for the perfect board, then you've probably come across the Uno and Nano. They're two of the most frequently used Arduino variations, but they serve different purposes.