Low frequency RFID works on the principle of radio waves and at the frequency of 125 KHz. There is a coil inside the RFID tag and when it is influenced by magnetic field, it sends an identity code to a device for further processing. (For more details, refer interfacing RFID with AT89C51).
The RFID tag is used as an identity for a particular user. If the identity (serial number of the tag) of the user is matched with the one already stored in this system, he gets immediate access through it. This RFID based secured access system also has many additional features. For example, a new user can register himself with the system. A registered user can also withdraw his entry from the system. These features can be accessed by pressing a tactile switch connected to the microcontroller.
In beginning, the user is prompted to scan his tag or ID. The serial code of the tag is identified by the reader module and is sent to AT89C51 for checking. If the ID is matched by the microcontroller, the user gets the access. On the contrary, if the tag is not identified, a message (‘Wrong ID’) is displayed on LCD screen.
A new user needs to press the switch to register after which his identity is verified twice with RFID tag. The new record is stored by the microcontroller to grant future access. The system also shows ‘Error’ if the tags do not match during verification. An existing user can delete his record by pressing the same switch. Again the verification is carried out and the user is deleted if the IDs match. If a different tag is scanned through the reader, LCD displays ‘you have shown different ID’.
When an RFID tag comes in this range, the reader detects it and sends a unique code of the tag serially. This serial code, consisting of 12 bytes, is received by the microcontroller. This code is treated as an ID for the user and is stored as an array in the microcontroller. If the ID is matched with this code, the user is granted access though the system. For more details on working and connections of the circuit, refer RFID interfacing through serial interrupt.