GSM MS boards on clearance: FC Caramel2

Mychaela Falconia falcon at
Sun Sep 3 04:03:50 UTC 2023

Hello GSM MS communities,

I have a large inventory of FC Caramel2 boards that are in need of
loving homes.  I mean these boards:

For those who are familiar with FCDEV3B, Caramel2 boards are very
similar: all FreeCalypso tools work exactly the same (even with the
same -h fcfam target selector option), firmware functionality works
exactly the same (fcdev3b and tangomdm fw builds are made from the
same source, just minor electrical diffs between the two boards which
the fw needs to know about), same AT command interface, same rvinterf,
same everything.  Vadim (fixeria) recently told me that he found FC to
have better CSD support than any other commonly available commercial
GSM modem - this aspect will work exactly the same on C2 as on FCDEV3B.
And for those who have an irresistible need to be naughty boys and run
naughty software, OBB can run on Tango/Caramel2 hardware too:

The main diff between FCDEV3B and Caramel2 is that C2 came out a little
worse in terms of quality:

* FCDEV3B analog audio circuits (loudspeaker and mic) came out very
clean despite no special effort at design time: I never hear any "buzz"
from rectified GSM RF in FCDEV3B analog audio.  OTOH, with C2 the audio
is dirty by default, and to get it mostly-clean, I have to insert a
long coax between the antenna connector on the board and the actual
antenna, to move the radiating element away from the analog audio

* LEDs: the single green LED on FCDEV3B indicates 100% reliably if the
chipset is switched-on or switched-off, but Caramel2 board LEDs
sometimes exhibit erratic behaviour as a result of wayward current
paths, as I explain in the Status Report and User's Guide document:

Seeing that Caramel2 design is flawed, I won't be making any more of
them: *if* I decide to produce another board in the future with similar
functionality, it will need to be a new design, adding LVC buffers for
proper PPD support (partial power-down) and reworking the audio
circuits.  In this light, the existing inventory of C2 boards needs to
be put on clearance - they are just gathering dust right now, but they
should be perfectly suitable for more casual users with less stringest
quality requirements.

I have enough stock to supply 12 complete kits consisting of:

* Caramel2 main board;
* FT2232D-based DUART28 adapter board;
* Power adapter from universal AC (worldwide voltage and frequency
  range) to 3.6 VDC;
* Possibly FC-HDS4 headset and quadband GSM antenna.

Once again, this board is a *clearance* item - no more will be made,
but the already-made ones are looking for loving homes.

*IF* there is any community interest in these boards, I would be happy
to ship a few to Sysmocom, to be further distributed via the webshop.
It would also be helpful if those who are interested in these clearance
boards (if any) could state what they would consider to be a fair price
for a full kit as described above.


P.S. If anyone still does CalypsoBTS hacks, these boards would NOT be
a good choice for it, as the Rx SAW filters are totally inaccessible
to rework - all 4 SAW filters (for full quadband Rx) are integrated
into a monolithic chip-like module from Epcos, which is then embedded
into the TR-800 module which is not amenable at all to rework.  However,
if you merely wish to see what's inside that TR-800 module, without
modifying it, we have published results of a complete PCB reverse eng
job on it:

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