nanoDLP

send me a link to the banggood stepper driver board pls and ill see if i can help out

I'm using a A4988/DRV8825 3D Printer Stepper Motor Driver Control Extension Shield Board GM
with a Hobbypower StepStick 4-layer DRV8825 Stepper Motor Driver Module A4988

I'm trying to wire this directly to the Raspberry pi3 (based on the prior linked diagram) in order to reduce the cost for the build.

Hi, I've made some PCB's following the diagrams on the download section, unfortunately the BOM is not complete and some components are no longer in production. Has anyone done something like that and could help me? thank's

Yes, i think its fair to assume the 4th pin is ground and a reference for the S,D & E signals.

Set all the DIP switches to "ON" to give 32 microsteps on the DRV8825   ( 200 X 32 = 6400) So 6400 steps will give you 1 rotation of the stepper motor ( assuming you're using a 1.8 deg stepper motor = most common Nema 17)

VM and the adjacent G(nd) pin are for 12VDC for the motor ( needs at least a 1.5 amp power supply)
5V & G(nd) are from the Raspi
( note its always important that the Gnd from the Raspi & Gnd from the VM are tied together which I believe is the case on the 2 middle pins of the 4 pin power in arrangement)

SHould indeed give a finer resolution.  All it means is that 12800 steps will equal 1 rotation.
If for example, you use a lead screw with a 2mm pitch, 12800 steps will give you 2mm of Z travel.

Not sure exactly with direct control but normally a "steps/mm" ( steps per millimeter) is required as a configuration input So using the example above you would input 6400 as being the steps required to travel Z 1mm