For this project you will need:

• Arduino board (25 €)
• RFID Reader (ID-20/ID-12) (24 €)
• RFID Adaptor (20 €)
• RFID Tag (1 €)

Total costs: 70 €

Instructions:

1. Mount the RFID reader into the adaptor socket
2. Install PuTTY on your computer
3. Connect the sensor to your computer through a USB cable
4. Scan the tag and you should see a unique code displayed on the terminal, such as: 2500ABF31C58. This is the tag’s identification code. You use PuTTY to find out what code does the tag has in order to use it on your algorithm
5. Connect the adaptor (including the sensor which is already connected) to the Arduino board specifing the following diagram
   

   RFID	Arduino
   1. Tx	D.P. 2
   2. Rx	D.P. 3
   3.
   4. GND	GND
   5. +5V(DC)	+5V

6. Upload this code to Arduino board
7. Connect your relay switch (5 V) to Pin 7 (digital) in order to command your door lock or a led when the tag is scanned.

(source: http://bildr.org/2011/02/rfid-arduino)