Chipcard Security SystemIn my last year at high school, we had to do a 'big' project for our Physics classes. I chose to design and build a chipcard security system.
The system uses the I2C protocol to communicate between the host computer and all the cardreaders. Up to 32 readers could be connected to the same (serial) bus. Special I2C chipcards are used to store a keycode.
The core of the system is the PCF8574, which is an I2C I/O expander. This I/O expander controls a electric door-opener and a 4066 switch to connect the local I2C bus (for the chipcard) to the I2C host bus. To increase the maximum I2C cable-length, a P82B715 is added to the design as an active pull-up device. A RC network is used as a timeout timer for both the door-opener lock and the 4066 switch. This is needed since a defective I2C card can lock-up the whole system.
To increase the number of addressable devices from the standard 8 to 28 addresses, a trick was used. The PCF8574 was configured to 'reprogram' its own I2C address, depending on the upper 4 bits of the I/O port on the expander.
Although it is not acceptable as a real security system, it works very well, even with 300 meters of UTP cable between the computer and 1 reader!
Schematics and PCBChipcard Security System reader (schematics only)
Chipcard Security System interface (schematics only)
Also the report is available (in Dutch only):
Chipcard Security System report