In message , at 21:23:14 on Sat,
1 Dec 2012, Theo Markettos remarked:
Fair enough, but what will happen (soon) on a London Bus: which of the
two elements will "win"; or will it refuse to pick either, claiming you
are trying to use more than one card at once?

I'd imagine the Oyster element would 'win', but lets wait and see.

What happens if the Oyster is out of credit?

Most of the Onepulse Oyster cards will have auto-topup enabled I would
have thought. They were obtained by early adopters (of the dual
functionality) and it's unclear why such credit-card loving folks would
depend on manual topup.

Does it automatically debit
the PayWave half instead? What happens if your Oyster has insufficient
credit for an all-zones tube journey? Does it decide which element to
charge it to when you touch out? What happens if you make another journey
and hit your daily cap? Does it charge the two journeys to Oyster and a
fractional journey to reach the cap to PayWave? Sounds like coding all the
corner cases could be tricky...

It's far too ambitious to expect the card to switch on the fly between
modes as the result of the sort of criteria you mention. It's going to
be designed to pick one of the two modes and stick with that.

Although if it is on manual topup and the Oyster element is empty, it
would be useful for it to always pick Paywave (irrespective of what it
might have picked had there been plenty of credit).

But if the answer is "the card won't work", then no doubt it will be
fixed by publicising the circumstances where it doesn't work, rather
than providing a complex technological fix.
--
Roland Perry