text: Download: Stepper is included with Arduino
  Small stepper motors designed for 5 volts may be able to run from
  power provided by USB. Larger motors will require separate power.
  Create an instance of the Stepper library for a unipolar type stepper motor.
  You will need to create an instance for each motor, giving each motor
  a unique name of your choice.
  Create an instance of the Stepper library for a bipolar type stepper motor.
  Sets the speed, in rotations per minute.
  Move the motor 1 or more steps. The number can be positive or
  negative, to specify the direction of movement.
  /* MotorKnob - slightly modified
  *
  * A stepper motor follows the turns of a potentiometer
  * (or other sensor) on analog input 0.
  */
  #include <Stepper.h>
  // the number of steps on your motor
  #define STEPS 200
  // create an instance of the stepper class, specifying
  // the number of steps of the motor and the pins it's
  // attached to
  Stepper stepper(STEPS, 7, 9, 8, 10);
  // the previous reading from the analog input
  long previous = STEPS / 2;
  void setup()
  {
  // set the speed of the motor to 30 RPMs
  stepper.setSpeed(30);
  }
  void loop()
  {
  // get the sensor value. This equation maps the
  // analogRead range to the number of steps, so the
  // motor nicely tracks a potentiometer's position
  long val = (long)analogRead(0) * STEPS / 1024;
  // move a number of steps equal to the change in the
  // sensor reading
  stepper.step(val - previous);
  // remember the previous value of the sensor
  previous = val;
  }
  TODO: schematic for circuit in photo above (2N3904 transistors, 1N4936 diodes, 1K resistors)
  TODO: how to identify the common wire using a multimeter, and trial-error to get the windings sorted out
  TODO: suggested schematic using an "easy" H-bridge chip
  TODO: how to identify each winding usine a multimeter