ULN2003 board stepping its LEDs on an Arduino Uno

// A 28BYJ-48 stepper on its ULN2003 board: one turn forward, one back.
//
//   ULN2003 IN1 -> pin 8    IN2 -> pin 9    IN3 -> pin 10    IN4 -> pin 11
//   ULN2003 +   -> 5V (on the bench, the breadboard power module)
//   ULN2003 -   -> GND
//
// A stepper does not spin when you power it. It turns one small step each
// time the coils are switched in the right order, so the code decides exactly
// how far it goes. Through its gearbox the 28BYJ-48 takes 2048 steps for one
// turn of the output shaft.
//
// The Stepper library wants the pins as IN1, IN3, IN2, IN4: that is why the
// constructor says 8, 10, 9, 11. Given 8, 9, 10, 11 the motor hums and does
// not turn.

#include <Stepper.h>

const int STEPS_PER_TURN = 2048;
Stepper motor(STEPS_PER_TURN, 8, 10, 9, 11);

void release() {
  for (int pin = 8; pin <= 11; pin++) digitalWrite(pin, LOW);
}

void setup() {
  motor.setSpeed(15);  // revolutions per minute; this motor manages about 15
  Serial.begin(9600);
  Serial.println("Mokxi Uno: stepper on pins 8 to 11");
}

void loop() {
  Serial.println("one turn clockwise");
  motor.step(STEPS_PER_TURN);
  release();
  delay(500);
  Serial.println("one turn back");
  motor.step(-STEPS_PER_TURN);
  release();
  delay(500);
}