>For inductive charging, you're talking a transformer basically - The one
>side can be driven with an AC field, to charge, when you detect a load
>(Impedance change) you know you're possibly connected, rectify in the
>receiving unit to give power to recharge the battery (Possibly have to
>charge that battery over some time IIRC, so maybe connection should be
>separate from recharge?)


Chris,

I've been reading this thread and it seemed to be covered well enough by
others but possibly if you can describe your environment slightly more fully
I may be able to offer some advice. I have been involved with development of
inductive power transfer and bidirectional signalling. Usually the distances
involved are as small as possible - typically mm to cm range but larger
distances can be accommodated in special circumstances - see below.

You were talking about a required detection range of several feet and this
is indeed hard in the general case with inductive methods BUT it may well be
possible to develop a special case which has adequate flexibility. By using
a large flat loop which the user walks over you could position them anywhere
within the loop.
I am not sure whether your user consciously comes to the download point or
whether the data transfer happens with the user unawares during other
operations.

If a loop as above was positioned across the width of a corridor you could
probably arrange data transfer as they walked along the corridor depending
on data rate and amount of data to be sent. Alternatively, if the user is
intended to cooperate, the system could detect their presence and ensure
that they were stable and suitably instructed before commencing download. I
have seen systems in use which use a loop perhaps 2 metres across and
perhaps 10 metres long which induce power into units within the confines of
the loop.

Can you comment further on the human interaction and general environment
aspects.


regards,



      Russell McMahon
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