Three-speed fan on an L293D (pins 9 and 10), on an Arduino Uno

// A desk fan with three speeds: each press of the button steps it up.
//
//   button: one side -> 5V, the other -> pin 2 and 10k to GND
//   L293D 1A -> pin 9   2A -> pin 10   1,2EN -> 5V
//   L293D 1Y and 2Y -> the motor   VCC1 and VCC2 -> 5V   GND -> GND
//   the LED is the Uno's own, on pin 13
//
// The L293D's enable pin is tied high, so the chip is always on and the two
// inputs decide everything: pin 9 held LOW and a PWM value on pin 10 turns the
// motor one way at that speed. The button cycles 0, 150, 200 and 250.
// A press is only believed once it has held for 50 ms (debouncing).

const int BUTTON = 2;
const int LED = 13;
const int IN1 = 9;
const int IN2 = 10;
const int SPEEDS[4] = {0, 150, 200, 250};
const char *NAMES[4] = {"off", "slow", "medium", "fast"};

int speed = 0;
int stable = LOW;
int last = LOW;
unsigned long changedAt = 0;

void setup() {
  pinMode(BUTTON, INPUT);
  pinMode(LED, OUTPUT);
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: fan. Press the button on pin 2 to change speed.");
}

void loop() {
  int now = digitalRead(BUTTON);
  if (now != last) {
    last = now;
    changedAt = millis();
  }
  if (now != stable && millis() - changedAt > 50) {
    stable = now;
    digitalWrite(LED, stable);
    if (stable == HIGH) {
      speed = (speed + 1) % 4;
      Serial.println(NAMES[speed]);
    }
  }
  analogWrite(IN1, 0);
  analogWrite(IN2, SPEEDS[speed]);
}