I am going to double check all connections with a multimeter then. One thing that is not clear to me is if I should connect the RESET pin with the SLEEP pin, which is in turn connected to GPIO23 on the RPi3. It does not say anything on the Readme file ( https://github.com/rkaczorek/astroberry-diy/blob/master/README ), but it is usually connected as shown in many other images on Google (see here ).

Regarding Vref, it should be measured between the GDN pin powering the board and the top of the potentiometer, right? The Nema 17 has a nominal current limit of 1.5 A monophase (does it mean "per coil"?). What value should Vref be set to? 3 V?

Do I need to power the motor via Vmot (nominal tension 3.45 V) or is the board powering it via Vdd?

Sorry for all these questions, which you might find stupid or obvious, but this is the first time I deal with stepper motors.