// Define pin connections & motor's steps per revolution
const int dirPin = 6;
const int stepPin = 7;
const int stepsPerRevolution = 200;

void setup()
{
  Serial.begin(9600);
	// Declare pins as Outputs
	pinMode(stepPin, OUTPUT);
	pinMode(dirPin, OUTPUT);
  Serial.println("start");
}
int speed = 1000;
void loop()
{
  if (Serial.available() > 0)
    {
      int inByte = Serial.read();
      
      switch (inByte)
      {
        case 'f': {
          if (speed>0){
            speed -= 100;
          }       
        }
        break;
        case 's': {
          if (speed<2000){
            speed += 100;
          }
        }
        break;
        case 'd': {
          digitalWrite(dirPin, LOW);
        }
        break;
        
        case 'e': {
          digitalWrite(dirPin, HIGH);
        }
        break;
      }
      
      } 
      for(int x = 0; x < stepsPerRevolution; x++)
      {
        digitalWrite(stepPin, HIGH);
        delayMicroseconds(speed);
        digitalWrite(stepPin, LOW);
        delayMicroseconds(speed);
      }
}