Hi friends. For those of you still interested in this endless trap I've got into, some update on the situation:
This last module is by far the hardest. I tried first on breadboards, then universal PCBs, then breadboards again... Each of them with his own pains and suffering.
Now I'm changing the approach and doing it on custom designed PCB, as all the other modules. The reasoning is that the basic functionality is already proved on breadboards and for the others is very hard to deal with soooo many jumpers lying all around and that's driving me crazy.
So I will design a PCB that leave "room for error" on the untested parts, that is, the fundamental ICs connections will be left open and connected on the soldering phase.
I hope that works. Will be finalizing the design and ordering the PCB board soon.
Thanks for reading.