New Calypso hardware being built

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New Calypso hardware being built

Spacefalcon the Outlaw
Hello ladies and gentlemen,

A little under a year ago Mr. Sean Moss-Pultz released Openmoko's
original PCB design files for GTA02 revisions A1 through A6:

ftp://ftp.freecalypso.org/pub/GSM/GTA02/GTA02_design_files.zip

Fast-forwarding to the present, I am now working together with an
anonymous company in a non-Western, non-1st-world region, and we are
jointly producing a new Calypso modem board that is based on a direct
reuse of the modem section from GTA02_MB_A6.

The name of the project is FCDEV3B, which stands for FreeCalypso
development board, triband.  Yes, it is triband like the GTA02 - while
I still desire to go to quadband eventually, the change was deemed to
be too risky for our first board, hence we are playing it safe and
keeping the proven-working GSM RF section completely intact from the
GTA02, which necessarily includes keeping the triband RFFE.

The board will be 90x50 mm in size, and functionally it will consist
of a bare GSM modem with a bunch of interfaces brought out to
connectors.  A power input connector, an SMA connector for the GSM
antenna, headers bringing out both UARTs, JTAG and MCSI at 2.8V logic
levels.  A SIM socket, PWON and RESET pushbuttons, and analogue
loudspeaker and microphone circuits following TI's reference schematics
will be on-board.

We have made one change to the design which we hope shall fix the
infamous bug #1024.  Zero-ohm 0402 jumper-resistors at reference
designators R1003 and R1004 have been removed, and the power traces
have been connected straight through where these 0402 R footprints
used to be.  TI's reference schematics (unfortunately TI's reference
layout appears to have been lost) prescribe star routing for the V-DBB
power net, and they have STAR_CONFIG "pseudo-component" symbols in the
two branches, but turning these "star points" into physical 0R jumper-
resistors must have been FIC/Openmoko's idea.  I believe that the
latter change contributed to bug #1024; with our change that
effectively reverts FIC/Om's change, the layout we have now appears to
match TI's intent as expressed on their Leonardo reference schematics,
hence I hope that the change we've made will be an improvement.

We are also going to populate a 22 uF cap at C214 (Leonardo refdes
corresponding to Om's C1009) instead of the originally-called-for
10 uF.  The hw rework for bug #1024 on Openmoko-made devices consisted
of likewise changing this cap to a higher value, or adding a second
10 uF cap in parallel, hence I hope that even if the bug does not get
fixed with our layout change, it will nonetheless be nipped in the bud
by our use of a larger capacitor.

But please feel free to look at our design files and judge for
yourselves:

ftp://ftp.freecalypso.org/pub/GSM/FreeCalypso/fcdev3b/

The latest revision as of right now is the one with 20160220 in the
filenames.  It still has a few outstanding issues which we are going
to fix, so it isn't 100% final yet, but the day when we declare our
design to be finished and send it out to PCB fab is approaching very
soon, hence I decided to give this list an opportunity to review our
work, particularly my thoughts regarding bug #1024 and my approach to
fixing it, before it is too late.

M~

P.S. When we get this board built and working, we are going to offer
them for sale to anyone who wants one on a retail basis, but we also
freely publish all of our design files, hence anyone else is free to
run their own production based on our design.

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