// slowly accelerate to desired motor speed - no library

const int dirPin = 2,
          stepPin = 3;

long usDelay,   // pause between half-step
     ramp = 50; // rate of acceleration

unsigned long timer,
         timeout = 1000,
         multiplier = 16; // start value multiplier, maximum = 16

void setup() {
  pinMode(stepPin, OUTPUT);
  pinMode(dirPin, OUTPUT);
  digitalWrite(dirPin, HIGH);

  for (usDelay = timeout * multiplier; usDelay > timeout; usDelay -= ramp) { // decrease step delay
    onestep(); // step the motor
  }
}

void loop() {
  if (micros() - timer >= timeout) { // use timeout value for constant rotation speed
    timer = micros(); // reset timer to wait for next pulse
    onestep();
  }
}

void onestep() {
  digitalWrite(stepPin, LOW);
  delayMicroseconds(usDelay);
  digitalWrite(stepPin, HIGH);
  delayMicroseconds(usDelay);
}