#include <Stepper.h>

static int en = 12;
static int ms1 = 3;
static int ms2 = 10;
static int stp = 5;
static int dir = 8;

void setup()
{
  pinMode(en, OUTPUT);
  pinMode(ms1, OUTPUT);
  pinMode(ms2, OUTPUT);
  pinMode(stp, OUTPUT);
  pinMode(dir, OUTPUT);

  digitalWrite(en, LOW);
  digitalWrite(ms1, LOW);
  digitalWrite(ms2, LOW);
  digitalWrite(stp, LOW);
  digitalWrite(dir, LOW);

  Serial.begin(9600);
}

void loop()
{
  if (Serial.available())
  {
    if (Serial.read() == 'A') {
      digitalWrite(dir, LOW); //CW
      digitalWrite(stp, HIGH);
      delay(10);
      digitalWrite(stp, LOW);
      delay(10);
    }
  }
}