const int led_red = 1;         // Output pins for the LEDs
  const int led_blue = 2;
  const int led_yellow = 3;
  const int led_green = 4;
  const int buzzer = 5;		 // Output pin for the buzzer
  const int red_button = 9;      // Input pins for the buttons
  const int blue_button = 10;
  const int yellow_button = 11; 
  const int green_button = 12;   // Pin 13 is special - didn't work as planned
  long sequence[20];             // Array to hold sequence
  int count = 0;                 // Sequence counter
  long input = 5;                // Button indicator
  int wait = 500;                // Variable delay as sequence gets longer
  
  /*
  playtone function taken from Oomlout sample
  takes a tone variable that is half the period of desired frequency
  and a duration in milliseconds
  */
  void playtone(int tone, int duration) {
    for (long i = 0; i < duration * 1000L; i += tone *2) {
      digitalWrite(buzzer, HIGH);
      delayMicroseconds(tone);
      digitalWrite(buzzer, LOW);
      delayMicroseconds(tone);
    }
  }
  
  
  /*
  functions to flash LEDs and play corresponding tones
  very simple - turn LED on, play tone for .5s, turn LED off
  */
  void flash_red() {
    digitalWrite(led_red, HIGH);
    playtone(2273,wait);             // low A
    digitalWrite(led_red, LOW);
  }
  
  void flash_blue() {
    digitalWrite(led_blue, HIGH);
    playtone(1700,wait);             // D
    digitalWrite(led_blue, LOW);
  }
  
  void flash_yellow() {
    digitalWrite(led_yellow, HIGH);
    playtone(1275,wait);             // G
    digitalWrite(led_yellow, LOW);
  } 
  
  void flash_green() {
    digitalWrite(led_green, HIGH);
    playtone(1136,wait);             // high A
    digitalWrite(led_green, LOW);
  }
  
  // a simple test function to flash all of the LEDs in turn
  void runtest() {
    flash_red();
    flash_green();
    flash_yellow();
    flash_blue();  
  }
  
  /* a function to flash the LED corresponding to what is held
  in the sequence
  */
  void squark(long led) {
    switch (led) {
        case 0:
          flash_red();
          break;
        case 1:
          flash_green();
          break;
        case 2:
          flash_yellow();
          break;
        case 3:
          flash_blue();
          break;
      }
      delay(50);
  }

  // function to congratulate winning sequence
  void congratulate() {
    digitalWrite(led_red, HIGH);       // turn all LEDs on
    digitalWrite(led_green, HIGH);
    digitalWrite(led_yellow, HIGH);
    digitalWrite(led_blue, HIGH);
    playtone(1014,250);                // play a jingle
    delay(25);    
    playtone(1014,250);
    delay(25);    
    playtone(1014,250);
    delay(25);    
    playtone(956,500);
    delay(25);    
    playtone(1014,250);
    delay(25);
    playtone(956,500);
    delay(2000);   
    digitalWrite(led_red, LOW);        // turn all LEDs off
    digitalWrite(led_green, LOW);
    digitalWrite(led_yellow, LOW);
    digitalWrite(led_blue, LOW);
    resetCount();                      // reset sequence
  }
  
  // function to reset after winning or losing
  void resetCount() {
    count = 0;
    wait = 500;
  }
  
  // function to build and play the sequence
  void playSequence() {
    sequence[count] = random(4);       // add a new value to sequence
    for (int i = 0; i < count; i++) {  // loop for sequence length
      squark(sequence[i]);             // flash/beep
    }
    wait = 500 - (count * 15);         // vary delay
    count++;                           // increment sequence length
  }
 
  // function to read sequence from player 
  void readSequence() {
   for (int i=1; i < count; i++) {               // loop for sequence length
      while (input==5){                          // wait until button pressed
        if (digitalRead(red_button) == LOW) {    // Red button
          input = 0;
        }
        if (digitalRead(green_button) == LOW) {  // Green button
          input = 1;
        }
        if (digitalRead(yellow_button) == LOW) { // Yellow button
          input = 2;
        }
        if (digitalRead(blue_button) == LOW) {   // Blue button
          input = 3;
        }
      }
      if (sequence[i-1] == input) {              // was it the right button?
        squark(input);                           // flash/buzz
        if (i == 20) {                           // check for correct sequence of 20
          congratulate();                        // congratulate the winner
        }
      }
        else {
          playtone(4545,1000);                   // low tone for fail
          squark(sequence[i-1]);                 // double flash for the right colour
          squark(sequence[i-1]);
          resetCount();                          // reset sequence
      } 
    input = 5;                                   // reset input
    }
  }  
  
  // standard sketch setup function
  void setup() {
    pinMode(led_red, OUTPUT);      // configure LEDs and buzzer on outputs
    pinMode(led_green, OUTPUT); 
    pinMode(led_yellow, OUTPUT); 
    pinMode(led_blue, OUTPUT); 
    pinMode(buzzer, OUTPUT);
    pinMode(red_button, INPUT);    // configure buttons on inputs
    digitalWrite(red_button, HIGH);// turn on pullup resistors
    pinMode(green_button, INPUT);
    digitalWrite(green_button, HIGH);
    pinMode(yellow_button, INPUT);
    digitalWrite(yellow_button, HIGH);
    pinMode(blue_button, INPUT);
    digitalWrite(blue_button, HIGH);
    randomSeed(analogRead(5));     // random seed for sequence generation
    //runtest();
  }
  
  // standard sketch loop function
  void loop() {
    playSequence();  // play the sequence
    readSequence();  // read the sequence
    delay(1000);     // wait a sec
  }