Based on: https://medium.com/jungletronics/uln2003-28byj-48-stepper-motor-f1cc5357eff

_61_ULN2003_HALF_STEP_DRIVE_03

// HALF STEP

#define stepper PORTB
#define waiting_time 500

void setup() {
  for (int z = 8; z < 12; z++) {

    pinMode(z, OUTPUT);             // pins 8,9,10,11 output for driving the motor

  }
}

void loop() {                       // Half Step Drive

  stepper = 0B0001;                 // 0x01;
  delay(waiting_time);

  stepper = 0B0011;                 // 0x03;
  delay(waiting_time);

  stepper = 0B0010;                 // 0x02;
  delay(waiting_time);

  stepper = 0B0110;                 // 0x06;
  delay(waiting_time);
  
  stepper = 0B0100;                 // 0x04;
  delay(waiting_time);

  stepper = 0B1100;                 // 0x0C;
  delay(500);

  stepper = 0B0001;                 // 0x01;
  delay(waiting_time);

  stepper = 0B1001;                  // 0x09;
  delay(waiting_time);
  
}