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• CARDS + one READER + one DECODER: each user possesses a
CARD and access is controlled by recognising the CARD code when
it is held in front of the READER (Figure 2).
In spite of their apparent simplicity, the transponders CARDS really
contain a complex circuit which allows the READER to recognise the
code identifying each single card when it is held in front of it.
Depending on how they are programmed, all the CARDS may activate just
one of the two outputs or, alternatively, they may activate both outputs.
A mixture of the two possibilities is also possible, i.e., some CARDS may be
active on just one output and others active on both.
The READER acts as an aerial, that is, it recognises the CARD code
when it is held in front of it and sends it to the DECODER. The
READER must be placed in a practical and handy position to allow
users to hold their CARDS in front of it without difficulty.
2
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