[gta02-core] Calypso's last dance

Werner Almesberger werner at openmoko.org
Fri Jul 24 13:36:27 CEST 2009

?lvaro Lopes wrote:
> Is height the only showstopper here, or do we have concerns about PCB area
> too ?

Height seems to be the main factor. The Calypso covers a large surface
but is flat. So if we want to make things fit into the GTA02 case, we
have to have a similar structure. Most of the modules needs a smaller
surface but are thicker.

Some of the thickness comes from having two two PCBs stacked on each
other - the main PCB and the modem's PCB. In the case of modules with
a socket, one could make an FPC cable to attach them, but that would
be fragile and yet another new item that needs to be made.

> I'll be honest here. I see Calypso as a dead end.

It's very dead indeed. There are two reasons why I didn't kill it yet:

- we get it "for free" (no material and sourcing cost) along with the
  other components

- there was talk about making a mass-produced device that would closely
  follow gta02-core, so we would have basically absorbed one prototype
  spin of that device. This now seems unlikely, so there's no extra
  value in keeping the Calypso.

> [I'm investigating how to get those 3A peak
> without disturbing the PMU too much, in case we go after option's chip]

I think something like the current arrangement, with going directly
to the battery and without the PMU knowing any of this, is be the
canonical way to solve this.

This means that the PMU will have misleading information about battery
current and even charging state, but this seems unavoidable.

Thinking about it ... there might actually be a possibility to do
better. If we tapped into Vsys instead of Vbat, the PMU would know
what we're doing. This would limit the available current to 2.2 A
(50633 manual, table 91, Ilim(BAT-SYS)), so either some buffering
would be needed for the peaks, or an external "ideal diode" from
Vbat to Vsys to boost the one inside the PMU (figure 38).

> A question for you all: if we have one decision on top of the table
> like: "Shall we go for a 3G GSM chip, for which we have enough
> documentation, and drop WLAN module, or keep the WLAN module and
> blindly integrate our old, EOL, obscure GSM 2G chip ?"
> what would we choose ?

Visit the local Telit distributor and get a few of their very nicely
documented GSM modules ? :-)

- Werner

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