[Gta04-owner] GTA04 thermal imaging

NeilBrown neilb at suse.de
Wed Feb 15 12:16:18 CET 2012

On Wed, 15 Feb 2012 08:08:29 +0100 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

> Am 15.02.2012 um 03:01 schrieb NeilBrown:
> > 
> > Does just unplugging the RS-232 cable reduce power drain in suspend?  That
> > would be good.
> I think one of Christoph's images shows that. And the data sheet says:
> POWERDOWN:	1 - 10 uA
> No Load:		0.3 - 1 mA (this may be less than the IrDA receiver)
> There is no specification about the load currents. But they are multiplied
> since the charge pump has not the best efficiency.
> So I would assume 5 mA for each mA at the outputs.
> Anyways this means that if there is no RS232 cable plugged in (which is
> the normal operation case for the plain user), there should not be more
> than 1 mA i.e. 3 mW. This can't be the reason why suspend does not
> work well enough.

Seeing that all my testing has been with the RS-232 cable plugged it, it could
be the reason why I'm not measuring as low a current as I expect.

I've just performed tests with 3.2 with as much turned off as possible.

With the RS-232 cable plugged in I've measures 65 and 68 mA.  This is over
120-150 seconds and it takes a little while to get into and out of suspend so
there is room for a few % error.
With the RS-232 cable not plugged in I've measured 51 and 48 mA !!!

This suggests 15-20 mA (at about 4V) is warming the RS-232 driver.

I checked the wiring and it looks OK.
The three outputs (which I was thinking might be shorted to something) are
red, orange, and blue, which are wired to pins 9, 8, and 2 (though the System
manual says 9, 7, and 2:  7 and 8 are swapped!!).
These are documented as inputs and I cannot see any shorts, so it looks good.

But something is pulling  15 mA through the RS-232 driver!

Fortunately this is easy to fix - unplug the RS-232 cable!

50mA standby with 1000mAH (assuming battery as lost some of its capacity)
means 20 hours of standby time.  That is almost usable!!

> Other ideas for suspend:
> * is the USB3322 powered down (GPIO 174 = 0)?
> * is the GPS module switched of (or does it switch on unintentionally by power-down)?
> * does the video amplifier OPA362 remain disabled (GPIO23 = 0)?

I'm pretty sure I've checked all of those.


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