see: https://medium.com/@J.3/jaythree-balancing-car-project-part-2-3-315dd25e0c3b

_35_ProMini_StepDownConverter_DRV8825_StepperMotor_02.ino

#define DIR 2
#define STEP 3
#define BUTTON A0

#define M0 4
#define M1 5
#define M2 6


int dPause    =  100;
int dirLevel  = HIGH;


void setup() {

  pinMode(DIR, OUTPUT);
  pinMode(STEP, OUTPUT);
  pinMode(M0, OUTPUT);
  pinMode(M1, OUTPUT);
  pinMode(M2, OUTPUT);

  pinMode( BUTTON, INPUT );

}

/* motor  FULL throttle */

void loop()
{

  delay(10);
  digitalWrite(M0, LOW );
  digitalWrite(M1, LOW  );
  digitalWrite(M2, LOW  );


  digitalWrite( DIR, dirLevel );
  stepGo();
}

void stepGo() {

  digitalWrite(STEP, HIGH);
  delayMicroseconds(dPause);
  digitalWrite(STEP, LOW);
  delayMicroseconds(dPause);

}