Day 20

//Use Hardware and Timer Interrupts for Fun with Sound
//Include the TimerOne library
#include <TimerOne.h>
//Button pins
const int BUTTON_INT=0; //Interrupt 0 (pin 2 on the Uno)
const int SPEAKER=12; //Speaker on pin 12
//Music keys
#define NOTE_C 65
#define NOTE_D 73
#define NOTE_E 82
#define NOTE_F 87
#define NOTE_G 98
#define NOTE_A 110
#define NOTE_B 123
//Volatile variables can change inside interrupts
volatile int key = NOTE_C;
volatile int octave_multiplier = 1;
void setup ()
{

//Set up serial
Serial.begin(9600);
pinMode (SPEAKER, OUTPUT);
//The pin is inverted, so we want to look at the rising edge
attachInterrupt(BUTTON_INT, changeKey, RISING);
//Set up timer interrupt
Timer1.initialize(500000); // (.5 seconds)
Timer1.attachInterrupt(changePitch); //Runs "changePitch" on each
//timer interupt
}

void changeKey()
{
octave_multiplier=1;
if (key == NOTE_C)
key = NOTE_D;
else if (key == NOTE_D)
key = NOTE_E;
else if (key == NOTE_E)
key = NOTE_F;
else if (key == NOTE_F)
key = NOTE_G;
else if (key == NOTE_G)
key = NOTE_A;
else if (key == NOTE_A)
key = NOTE_B;
else if (key == NOTE_B)
key = NOTE_C;
}
void changePitch()
{
  octave_multiplier=octave_multiplier*2;
  if(octave_multiplier>16)octave_multiplier=1;
  tone(SPEAKER, key*octave_multiplier);
}
void loop()
{
  Serial.print("Key: ");
  Serial.print(key);
  Serial.print(" Multiplier: ");
  Serial.print(octave_multiplier);
  Serial.print(" Frequency: ");
  Serial.println(key*octave_multiplier);
  delay(100);
 
}