Hi Raj,

I designed a lot of such contactless card readers using at89c2051.
They are stand alone and ( or ) network card readers.
The program ( less then 2K ) manages the RF signal decoding (64 bits Manchester), the database manipulation and PC’s commands interpretation.
As a stand alone reader I used at24c04, 24c16 and Ramtron FM24C16 memories.
The uC is working on 11.059MHz.
Each Card has 40 bits of utile information so I allocated 5 bytes for each in the database .
For the at24c16 variant I can store 408+1 card in the memory ( including the key management card )
There are no switches used for the database management in the stand alone version ( only key card used)
As at26c2051 has not i2c interface, a software one is used but with speed less then 100KHz

Writing and reading to and from the database is random.
The program intelligently manages the memory to fill it entirely and avoid gaps.
The search algorithm is linear.
The program was written in asm.
The RF signal is decoding 3 times and a majority decision is taken for the utile information ( after removing the redundant bits)


Of course, I used one facility of 24c16 witch allow the reading of the entire memory by sending only once the address pointer and automatically incrementing it after each access.
I also used to read in the internal uC’s RAM 20 bytes at a time from eeprom.
The matching process is accomplished in RAM
The entire process of RF decoding and database searching takes less then 100ms
I can erase randomly a card from database in 25 ms or the entire data base in cca. 20 sec

I also mention this process is not optimized for speed but for ROM space ( uC’s constraints )

I can give you an idea ( not a technical approach ) about the reading speed.
One of my customer used such a reader mounting it vertically ( 80*50mm antenna and 20cm reading distance)
The card is gravitationally falling before the antenna and collected in a box.
During the vertical travel of the card in the front of the reader there is enough time to read, decode and find it in the eerom database.

I apologize for my English syntax but I hope this information will help you to design a speeder RFID card reader.


Best regards,

Cristian Ceausescu

elcris@k.ro