alexisgaziello:
One of my main problems is that I do not know how to set the connections (one cable for each pair of pins or we should also need a ground?).
I am also aware that the Arduino works on 5V and the raspberry pi on 3.3V. Should we connect a resistance in series or some voltage divider to avoid any over current?
Hi,
If you are using two different supplies ("chargers", USB, ...), you have to tie grounds together.
As the signal goes from arduino (keep an eye!, not all of them work at 5.0 V), you may do with a resistor divider, but I'd recommend to use a level shifter instead.
Regards.