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Subject: Re: AW: More aggressive Rockbox battery charging

Re: AW: More aggressive Rockbox battery charging

From: [IDC]Dragon <idc-dragon_at_gmx.de>
Date: 2005-02-11

> Patience... hopefully after the weekend I will have something to show
> the world. It will then require testing to make sure it is recharging
> acceptably and to make sure I haven't broken any of the other Rockbox
> platforms.

Excellent!

> Random observations:
> * I used the debug screen to observe the pre-diode battery charger
> voltage. As the battery gets charged, the voltage drop across the diode
> drops measurably. It isn't a huge amount, but it should be usable for a
> charge current estimate if we go that route. Unfortunately, this
> requires characterization before it would be usable.

If you lack some equipment (amp meter, lab supply), I can do this, if I find
time.

> * It would be nice to know what the scale factors of the A/D inputs are.
> The ones that are used are deducible (obviously). What is Vref for
> the A/D? 3.3v? 5v?

I think it's own supply, which is 3.3V. But we nesed to calibrate the
numbers anyway.

> * Interesting charger that works the same way as the Archos (thank you
> google):
> http://www.angelfire.com/electronic/hayles/charge1.html
> This does a soft-start -- that looks like a really good idea. For the
> first N minutes (4), apply a low charge rate (0.2C). This would help
> the problem of getting things going if the batteries are nearly
> exhausted but not hurt the batteries if they are already fully charged.

And then observe if the voltage rises (cells take charge) or not? Sounds
like a good idea.

> * The mysterious AN0 "poorly scaled" battery input looks to me like it
> is the threshold voltage at which the AJR hardware turns itself off.
> When that voltage drops below 2v the music dies. This may be usable to
> detect the "dangerously low" battery level more accurately. I haven't
> experimented with this at all.

I don't think this is related. The box just plain dies from undervoltage, no
A/D involved. We can estimate with the normal battery measurement channel.

Jörg

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Received on Fri Feb 11 16:02:05 2005

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