The trouble is that most of the manufacturers of cards and systems try to pack their product by features and promote them in a way that hides their - otherwise quite simple - nature; and if you search the web you will get too much of this rubbish to distinguish what is really needed.

One of the most used and easily available incarnation of smartcard is a combination of a microcontroller and an EEPROM. You can build one for yourself - try ggogling for "gold wafer" or "gold card" - these can be also bought in true plastic card form - in those "hobbyist" cards you will find PICs and AVRs (sorry, no '51...). The interface on the golden pads is nothing more than supplying power and clock to the mcu and a bidirectional UART communication line, basically Rx and Tx tied together. In principle you can program the mcu as you wish, but there are established standards for communication (ISO7816).

What the manufacturers provide as extra are "smarter" and/or more secure cards (the "hobbyist" card can be in principle opened up and there are physically 2 chips inside, with "bare" communication line between them), and an "OS" which is a tool to develop applications easily - to store and retrieve data in some systematic manner ("filesystem"), to encrypt communication, and alike.

To grab the idea, first build a reader (see e.g. the epanorama links - Computer interfaces at http://www.epanorama.net/links/smartcards.html - you can try to buy one but some of them are "too smart" and hide the communication - and you will learn if you build it yourself) for PC's COM port and get a GSM SIM card and some software from the links to "talk" to it... You will see there is no miracle in it and I'll bet you will be able to build a '51-based reader/controller easily. The "OS" on the card itself is again a matter of either getting it ready-made, or self-tailoring it according to possible requirements.


Jan Waclawek