On Tue, Oct 04, 2022 at 11:47:43PM -0800, Mychaela Falconia wrote:
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?
you are right, the GPIO of the SAM3S are 3.3V only, and are not 5V tolerant. I do not know how the input protections of this MCU are (and could not find it in the datasheet).
I just tried it on the VCC phone pin, at 5V with current limit set to 50 mA, and it drew 50 mA, indicating a protection diode probably tired to protect the pin. the pin and MCU survived fine, but I did not stress it for over 5 seconds, and would not recommend using it with 5V.
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?
before SIMtrace, there were the RebelSimCard boards (with pin header for the sim signals), but these are not available since long. I don't know of any other adapter board for the FPC with pin header for the signals. If you don't want to create a board, you could just use a SIMtrace board and desolder the MCU (e.g. using hot air). the signals would be available on the connector, MCU pins, or card slot. the bus switch on the board is 5V tolerant, but to forward the signal to the actual SIM card, you need to set its pin 1 and 19 low (the lines are floating once the MCU is gone).