On this instructable I will try to show how to interface a RFID sensor with the Arduino. I am using the RFID sensor from seeedstudio the serial version of it. There are a few parts you will gonna need. I also bought some RFID keys.
Connect the antenna on the appropriate pins like the first photo.
Plug the RFID sensor to the protoboard like the second photo above.
Only 3 wires are required to interface, 2 wires for supply and another for the serial line(communication) The wires as connected as the third photo shows. On RFID sensor: PIN 1 -> Tx PIN 2 -> Rx (Not Used) PIN 3 -> NC PIN 4 -> GND PIN 5 -> VCC (+5V)
Tx from RFID board goes to Digital PIN 2 on Arduino Board.
That is all you gonna need to wire.
Moving on to next step, the software.
Step 3: The code
I'm not a software guy, so this code is just for demonstration.
I don't make any kind of checksum at the tags code, but it seems to work fine.
The code is really simple. I used a new library for the serial, using software emulation.
With the two white cards you can deny or allow the access of others keys.
Any doubt, please ask me.
code update for new Arduino version