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