ULN2003A

// 512 moves is full spin
int stepMotor_moves = 256;
// How fast magnets will change in ms
int stepMotor_delay = 5;
// pins as IN1, IN2, IN3, IN4
int stepMotor_pins[] = {8, 9, 10, 11};

void setup() {
  // Arduino pin config...
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  // Run functons once
  stepMotor_moveForward();
  stepMotor_moveBackward();
}

// Arduino loop...
void loop() {
}

void stepMotor_resetMagnets() {
  digitalWrite(stepMotor_pins[0], LOW);
  digitalWrite(stepMotor_pins[1], LOW);
  digitalWrite(stepMotor_pins[2], LOW);
  digitalWrite(stepMotor_pins[3], LOW);
}

void stepMotor_moveForward() {
  stepMotor_resetMagnets(); // reset magnets before looping step motor
  for (int j = 0; j < stepMotor_moves; j++) {
    // Forward - power on magnets in 1, 2, 3, 4 config with delay every change
    for (int i = 0; i < 4; i++) {
      if (i == 0) {
        digitalWrite(stepMotor_pins[3], LOW);
        digitalWrite(stepMotor_pins[0], HIGH);
      } else if (i == 1) {
        digitalWrite(stepMotor_pins[0], LOW);
        digitalWrite(stepMotor_pins[1], HIGH);
      } else if (i == 2) {
        digitalWrite(stepMotor_pins[1], LOW);
        digitalWrite(stepMotor_pins[2], HIGH);
      } else if (i == 3) {
        digitalWrite(stepMotor_pins[2], LOW);
        digitalWrite(stepMotor_pins[3], HIGH);
      }
      delay(stepMotor_delay);
    }
  }
  stepMotor_resetMagnets(); // release magnets
}

void stepMotor_moveBackward() {
  stepMotor_resetMagnets(); // reset magnets before looping step motor
  for (int j = 0; j < stepMotor_moves; j++) {
    // Forward - power on magnets in 4, 3, 2, 1 config with delay every change
    for (int i = 0; i < 4; i++) {
      if (i == 0) {
        digitalWrite(stepMotor_pins[0], LOW);
        digitalWrite(stepMotor_pins[3], HIGH);
      } else if (i == 1) {
        digitalWrite(stepMotor_pins[3], LOW);
        digitalWrite(stepMotor_pins[2], HIGH);
      } else if (i == 2) {
        digitalWrite(stepMotor_pins[2], LOW);
        digitalWrite(stepMotor_pins[1], HIGH);
      } else if (i == 3) {
        digitalWrite(stepMotor_pins[1], LOW);
        digitalWrite(stepMotor_pins[0], HIGH);
      }
      delay(stepMotor_delay);
    }
  }
  stepMotor_resetMagnets(); // release magnets
}