Hello SIMtrace community,
I just bought a SIMtrace v2 hw kit, and I am looking to use it for the
purpose of troubleshooting ancient phones. I've been working with
Calypso phones mostly, but now I am traveling farther back in time in
the history of GSM, playing with phones from 1990s. I bring these
phones up on my own GSM network run with a sysmoBTS plus Osmocom CNI
sw stack, and I use programmable SIMs of which I bought a semi-custom
batch from China a year and a half ago, semi-custom batch meaning my
own artwork on the plastic and my choice of 2FF-only cut, but the
actual module is unmodified off-the-shelf, the only thing I could get
as a low-dollar customer. These SIMs (I named my version FCSIM1)
appear to be identical to the model known in the Osmocom community as
GrcardSIM2, once sold as sysmoSIM-GR2.
Here is the issue: my SIMs work just fine in Ericsson I888, Nokia 5190
and Nokia 6190 - all 1990s phones - bringing these ancient phone onto
my Osmocom-based GSM network quite happily. But I am interacting with
another member of the vintage phone community (r/vintagemobilephones
on Reddit) who has a few working Nokia 2190s - a phone model from 1995,
one of the first PCS1900 band phones ever - and he tells me that this
super-ancient model is very finicky in terms of which SIMs it accepts.
There are several T-Mobile MVNOs who issue SIMs that still have the
classic GSM 11.11 SIM application present, and they work fine in most
ancient phones, including Nokia 5190 and 6190, but they don't work in
2190 - my contact tells me that he found only one MVNO (Lycamobile)
whose SIMs do work in the 2190. Intrigued, I sent him a few of my
FCSIM1 cards, he tested one in a 2190, and he tells me the ancient
phone rejects this SIM too. :-(
At this point the rational course of action ought to be to trace the
SIM-ME communication between the finicky phone and one of each kind of
SIM: the kind it accepts, and the kind it doesn't accept, and see what
it barfs on. But I just realized a problem: there is a very high
likelihood that the ancient phone feeds 5V to the SIM (Nokia 2190 is
powered by a 5-cell NiMH battery, so it has plenty of voltage headroom
inside to put out 5V), and my reading of Atmel's datasheet for the
SAM3S chip on the SIMtrace board tells me that 5V will fry it: the
electrical specifications chapter of the datasheet lists 4.0 V as the
Absolute Maximum Rating for all pins, including those GPIO pins that
are wired to the phone connection on the SIMtrace board.
Just checking to see if my understanding is correct: is SIMtrace v2
indeed absolutely NOT tolerant of phones that put out 5V toward the
SIM? Not tolerant to the point that it would not simply not work, but
would *fry* the SAM3S chip?
If the board part of SIMtrace v2 kit is of no use with ancient phones
that put out 5V, I reason that I should still be able to make use of
FPC cables: I just need a little adapter PCB that hosts a SIM socket
and a connector for the FPC to go into, with accessible points for
probing with an o'scope or a logic analyzer - it just needs to be a
purely passive, connections only PCB, without any ICs that would be
fried by high voltages. Would anyone happen to know if I can still
buy such an adapter PCB anywhere (I read that such were used in the
beginning of the project before the first custom SIMtrace board), or
will I need to spin out that adapter PCB myself?
TIA,
Mychaela
