From: Jerry Van Baren <gerald.vanbaren_at_smiths-aerospace.com>
Date: Fri, 11 Feb 2005 10:30:52 -0500

Hi Jörg,

[IDC]Dragon wrote:

[snip]

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

Darn. Time is what I'm missing :-/

What I'm thinking is a test load that periodically writes the
interesting parameters to a file. If we get a couple of people to run
the test load and collect the data, we should be able to figure it out.
  Of interest would be a couple of different battery capacities (just I
have 1500mAH OEM batteries) and supplies (e.g. Matthias' 9v).

>>* 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.

Yes, that was my guess. Unfortunately the schematic isn't 100% complete
  (grrrr would be nice if Archos would at least "leak" the schematic) so
I cannot tell what the scales are without opening the box, and I don't
want to do that because my only AJR is in Real Life[tm] use.

[snip]

>>* 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.

The way I'm reading the schematic, Vbatt gets scaled by R31 & R32
(unknown scale factor) and is then compared to 2.0v by U17B. When Vbatt
falls below (2.0*scale) volts, U17B effectively "pushes" the OFF switch.
  We can read (Vbatt/scale) on AN0 -- if it gets close to 2.0v, we know
we are about to be turned off involuntarily.

Thanks,
gvb
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Received on 2005-02-11