Hi Atom,
I will see if I can measure the current but at low current draws the
meter may not be entirely accurate. I'll give it a go though.
According to the datasheet, if I take CS1 high or CS2 low before the
power supply drops from 5V to battery 3V, then the current draw will
be 2uA (typical) up to 100uA (max). But the datasheet seems a bit non
specific about the timing of the chip select lines being at correct
levels prior to the supply dropping to 3V.
So I have a couple of theories as to why the battery is going flat
fast. First, the CS2 chip select line was not being pulled down to 0V.
I've placed a 10K pull down on that line. I am hoping that this, easy
to install, extra resistor will fix the problem.
Second, perhaps the timing of the shutdown of power from 5V to 3V (on
battery) is critical. If that is the case, then I can see a situation
where the chip select lines could be in the wrong state when the power
down occurs. In that circumstance, the battery will pull alot more
current while on battery. As I said though, the datasheet is doesn't
explain the timing very well. Nevertheless, if the one pull down
resistor doesn't fix the problem then I'll add a capacitor on the 3V
battery side of the power supply to the two static RAMs. This will
ensure that the chip select lines settle into their correct state long
before the memory power supply falls from 5 to 3V.
So I don't think this is a big problem, it is just going to take a
while to work out exactly what has to be done. I am hoping that the
single 10K ohm pull down resistor is all that is needed.
Zoinky makes a good point though. The button cell most certainly can
be replaced by two AA batteries. I like the button cell because it's
guaranteed not to leak all over the insides of your precious synth's.
I cringe thinking about the number of Poly's that have been sitting in
storage with batteries slowly decomposing all of the PCB's. I bought
one on ebay specifically because the case, joystick etc was in perfect
condition while the insides were completely acid wrecked.
I think the button cell should be OK in the long run. It is just going
to take a few months to be certain that it is set up just right. And I
wanted to warn everyone before they lose their patches.
Mike.
--- In korgpolyex@yahoogroups.com, Atom Smasher <atom@...> wrote:
>
> On Tue, 27 May 2008, korgpolyex800 wrote:
>
> > So, I had a look at the design and think I might have missed a
pull down
> > resistor that would reduce the current by about half. I've added the
> > pull down onto both of the HAWK-800 kits and I guess in about six
weeks
> > I'll know if it made any difference at all.
> =================
>
> do you have a multi-meter? measure how much current is moving
through the
> battery...
>
>
> > A single 6264 static RAM in standby mode uses between 2 and 50uA.
> ==============
>
> that's a big range... what determines the actual current?
>
>
> > The longer term solution is now being looked at. There are two
ways to
> > go about this. One way would be to use a rechargeable battery
scenario.
> > The other, would be to write patches into flash memory. I'll post
again
> > as soon as I come up with a solution.
> ================
>
> a slightly larger rechargeable battery (1/3 AA) would have a better
> amp-hour rating, and would last longer than a 2032. i've seen gear with
> original 10-15 year old lithium batteries running strong.
>
>
> --
> ...atom
>
> ________________________
> http://atom.smasher.org/
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>
> "In peace, sons bury their fathers.
> In war, fathers bury their sons."
> -- Herodotus
>