Matthew Geier wrote

On Fri, 29 Jan 2010 06:31:42 -0800, ticketyboo wrote:


- But, if more than one of those cards collects enough power to
operate,
the terminal then has to use the anti-collision mechanism specified
by
the standard (ISO 14443 in the case of Oyster and bank payment
cards -
and also for ITSO cards) in order to identify all the operating
cards,
send the ones that it doesn't want to communicate with to sleep,
and
then carry out its transaction.

My experience with having a (new) Singapore CEPAS ezlink in my
wallet is
an Oyster terminal says 'multiple cards presented' and then won't
continue until you remove the other cards from it's field so it only
sees
one.

And the Singapore card has a better antenna - I discovered that the
LU
gates were still getting upset - I had removed my oyster from my
wallet
and was placing it on the reader to open the gates - but as I walked
through the gates beeped. It dawned on me later, the Oyster pad must
have
been getting a response from the Singapore CEPAS card as I walked
through
the gate - at range of over 20cm between my hip pocket and the Oyster

reader pad. (The Oyster card being my my hand or back in my shirt
pocket
by this stage).

obviously you should wrap the Singapore card in tinfoil - err aluminium
foil - like an RFID passport.

But if you want hands-free entrance to your office block and the
anti-collision mechanism isn't implemented properly a lot of card
shuffling is going to have to take place.

--
Mike D