21/07/2004 20:46:50, "David Bisset"
<
david_bisset@itechnic.co.uk> wrote:
>I'd also like to see a 3v3 switcher and a 5v switcher.
Power is definitely going to be more cunning on this rev. There are
more, and lower, voltages to be generated, and the power section
of the PXA27X manual needs some careful reading, from both the
hardware and software points of view.
The old tactic of just using linear droppers becomes less efficient
as voltages drop and currents rise...
>This should be configurable to allow the board to work off a
single LiPo
>cell at 3.6v or a Nicad/Nimh stack of 4 cells at 4.8vish...
2.0X does that with no problems, and a decent efficiency. I'd like
to improve on it.
>Given that most balloons are in battery based products.
Speak for yourself - mine are used where power is plentiful :)
>Once that?s on board support for charging would be nice.
Yeah. Tricky. How do I do this without
a) people picking bits of lithium out of their hair
b) making 80% of the board area various charger circuits for
various battery types?
Battery charging is nasty, scary, and prone to explode when done
wrongly. I'm not sure that I want any part of it, especially if people
are playing mix&match. I'll definitely take advice on this part of the
circuit. In fact, if I don't get advice, it's not going on the board.
>Is it possible to integrate a micro with access to the right bits of
a
>charging circuit and leave the implementation open?
Possibly. off you go :)
>It may also be a good idea to add a micro so that the board has
a little
>more intelligence when in standby.
Yeah - for super-low standby, a micro has charm. However, I'm
not sure it belongs on Balloon. I can't make it all things to all users,
so the philosophy says to chuck it off the board, and have the user
do what they want. After all, it doesn't need to be on a 6-layer, 4-
thou process, so it doesn't need to be on Balloon.
Having something like a TI MSP430 micro (nice, low power, cheap,
decent free tools available) running the battery, charger, a few
wakeup lines, possibly a serial port or the like, would probably
convince me to let it on the board. Otherwise, I think it has to be a
user-add, on a user-board. (and 5uA is reasonable standby
current for a micro like that...)
> However we need to specify a very low cost minimum fit
>option to keep hobbyists happy.
Yes, very aware of this, wearing both hats.
>I'd suggest a target BOM cost of £50
>giving a possible selling price of about £150-£200. Lower if
possible...
Price and manufacturability. Gottit. Just the same as every other
project :) (as well as the eternal 'next week, and for free').
>If PXA27X is so new we may have trouble getting silicon since as
Steve
>points out 3G phones will take the lions share of production,
Ah - that's not the point I was trying to make, but yes... CPU
availability is always an issue. Scrounging around should yield the
relative trickle that we need, especially if any tentative customers
can twist arms at Intel / ARM / their distie. To be honest, though,
I'd expect Intel to be able to keep up with demand. They get a
fair few per wafer :)
However, CPU availability is an issue, no matter what we design in.
I don't see PXA27X as particularly risky.
>It's possible that the PXA27X is a step too far. Has Linux ported
to it
>yet?
This is my main concern. Without drivers, this thing's a
paperweight. Whie I guess it'll boot more or less like a PXA250,
drivers for the (optional, I guess) new hardware may be some time
in coming. However, most of the new bits aren't showstoppers,
and the core looks very familiar.
Speak now, or forever hold your peace, people!
Steve
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