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Proximity card
Proximity card
is a generic name for contactless integrated circuit devices used
for security access or payment systems. It can refer to the older
125 kHz devices or the newer 13.56 MHz contactless RFID cards,
most commonly known as contactless
smartcards.
Modern proximity
cards are covered by the
ISO 14443
(Proximity Card) standard. There is also a related
ISO 15693
(Vicinity
Card) standard.
Proximity cards use
an LC circuit. An IC, capacitor, and coil are connected in series.
The card reader presents a field that excites the coil and charges
the capacitor, which in turn energizes the IC. IC then transmits
the card number via the coil to the card reader. The card readers
communicate in
Wiegand
protocol that consists of a data 0 and a data 1
circuit. The earliest cards were 26 bit. As demand has increased
bit size has increased to continue to provide unique numbers.
Often, the first several bits can be made identical. These are
called facility or site code. |
