#include <AccelStepper.h> // Include the AccelStepper Library

// Define step constant
#define HALFSTEP 8

// Creates an instance
// Pins entered in sequence 1-3-2-4 for proper step sequencing
AccelStepper myStepper(HALFSTEP, 8, 10, 9, 11); 

void setup() {
  // set the maximum speed, acceleration factor,
  // initial speed and the target position
  myStepper.setMaxSpeed(500.0); //about the max for 28BYJ-48
  myStepper.setAcceleration(1);
  myStepper.setSpeed(5);
  myStepper.moveTo(1000);
}

void loop() {
  // Change direction once the motor reaches target position
  if (myStepper.distanceToGo() == 0)  //how far the motor needs to travel
    myStepper.moveTo(-myStepper.currentPosition()); //target position 

  // Move the motor one step
  myStepper.run();
}