int switchPin = 2;    // switch input
int motor1Pin = 4;    // H-bridge leg 1 (pin 2, 1A)
int motor2Pin = 5;    // H-bridge leg 2 (pin 7, 2A)
int enablePin = 12;    // H-bridge enable pin
int ledPin = 13;      // LED 

void setup() {
  // set the switch as an input:
  pinMode(switchPin, INPUT); 

  // set all the other pins you're using as outputs:
  pinMode(motor1Pin, OUTPUT); 
  pinMode(motor2Pin, OUTPUT); 
  pinMode(enablePin, OUTPUT);
  pinMode(ledPin, OUTPUT);

  // set enablePin high so that motor can turn on:
  digitalWrite(enablePin, HIGH); 

  // blink the LED 3 times. This should happen only once.
  // if you see the LED blink three times, it means that the module
  // reset itself,. probably because the motor caused a brownout
  // or a short.
  blink(ledPin, 3, 100);
}

void loop() {
  // if the switch is high, motor will turn on one direction:
  if (digitalRead(switchPin) == HIGH) {
    digitalWrite(motor1Pin, LOW);   // set leg 1 of the H-bridge low
    digitalWrite(motor2Pin, HIGH);  // set leg 2 of the H-bridge high
  } 
  // if the switch is low, motor will turn in the other direction:
  else {
    digitalWrite(motor1Pin, HIGH);  // set leg 1 of the H-bridge high
    digitalWrite(motor2Pin, LOW);   // set leg 2 of the H-bridge low
  }
}

/*
  blinks an LED
 */
void blink(int whatPin, int howManyTimes, int milliSecs) {
  int i = 0;
  for ( i = 0; i < howManyTimes; i++) {
    digitalWrite(whatPin, HIGH);
    delay(milliSecs/2);
    digitalWrite(whatPin, LOW);
    delay(milliSecs/2);
  }
}