SIMtrace phone-side VCC

Harald Welte laforge at
Sat Jul 27 01:23:48 UTC 2013

Hi Tom,

On Fri, Jul 26, 2013 at 04:55:32PM -0400, Tom Schouten wrote:

> For future version of the board, it might be interesting to tie the
> VCC pin to an ADC input, to detect different voltage levels so the
> firmware can wait until phone decides to use 3V.

this is more or less what we intended to do from the beginning, but
somehow there was an error in the schematic so we had to resort on this.

If I remember correctly off my head the story goes like this:

So the original idea was to always forward the same VCC voltage from the
phone to the sim card by means of a switch, and alternatively provide
the SIM-side VCC with voltage from a regulator.

However, as both the regolator output and the forward-switch output were
connected together, and the regulator could not deal with voltage beping
present at its output while being disabled, the circuit never worked as

We didn't touch the simtrace v1.x hardware for a long time, as Kevin
started work on a completely different v2.x hardware years ago.
However, due to lack of time and other projects, this never really
emerged beyond the early design phase (as far as I know).

If I was to do an updated version of simtrace, I would also move to an
at91sam3s instead of the at91sam7s, as the former has more USB endpoints
enabling the CCID + CDC-ACM simultaneous operation for the MITM mode.

- Harald Welte <laforge at> 
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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