Thanks all for your answers.
I could test it by myself but I said to myself that before toasting an Arduino board(which is very dear to me) I better first ask somebody that knows and understands much more than me on this matter.
In my mind when you connect the common ground of two power sources (motor and circuitry) that was as the ground is only as reference point of zero and the current gets consumed in each circuit, the motor takes Amps and the electronics mAmps. I don't know how the currents manage to stay separated tough they have common ground if not only for what's in the middle between each positive and ground.
So I thought that a Low pin can serve for this common ground function. Apparently not.
Well, given this stage I think I would choose the DPDT realy version because it can drive as much as the relay stands and I only need one PWM pin if I am not mistaking.
@MorganS, yes that is what I thought first but then maybe R3 and R4 should be a bigger value. And about charlieplexing, if they were diodes instead of resistors (or both) with cathode placed on the pin wouldn't this work then?
I went through and made the version with diodes. It looks better and it has a ground but the same question remains.
Thanks again.
