Using Interrupts to Drive Multiple Speakers Simultaneously from an Arduino

multi-speaker.ino

//** Arduino - Drive Multiple Speakers with Interrupts **//
//** http://www.jeremyblum.com/2010/09/05/driving-5-speakers-simultaneously-with-an-arduino/ **//

/* Timer reload value, globally available */
unsigned int tcnt2;

/* Toggle HIGH or LOW digital write */
int toggle1 = 0;
int toggle2 = 0;
int toggle3 = 0;
int toggle4 = 0;
int toggle5 = 0;

/* Keep track of when each note needs to be switched */
int count1 = 0;
int count2 = 0;
int count3 = 0;
int count4 = 0;
int count5 = 0;

/* Frequency Output Pins */
#define FREQ1 9
#define FREQ2 10
#define FREQ3 11
#define FREQ4 12
#define FREQ5 13

//Setup Function will run once at initialization
void setup()
{
    /* First disable the timer overflow interrupt*/
    TIMSK2 &= ~(1<<TOIE2);

    /* Configure timer2 in normal mode (no PWM) */
    TCCR2A &= ~((1<<WGM21) | (1<<WGM20));
    TCCR2B &= ~(1<<WGM22);

    /* Select clock source: internal I/O clock */
    ASSR &= ~(1<<AS2);

    /* Disable Compare Match A interrupt (only overflow) */
    TIMSK2 &= ~(1<<OCIE2A);

    /* Configure the prescaler to CPU clock divided by 128 */
    TCCR2B |= (1<<CS22)  | (1<<CS20); // Set bits
    TCCR2B &= ~(1<<CS21);             // Clear bit

    /* We need to calculate a proper value to load the counter.
    * The following loads the value 248 into the Timer 2 counter
    * The math behind this is:
    * (Desired period) = 64us.
    * (CPU frequency) / (prescaler value) = 125000 Hz -> 8us.
    * (desired period) / 8us = 8.
    * MAX(uint8) - 8 = 248;
    */
    /* Save value globally for later reload in ISR */
    tcnt2 = 248;

    /* Finally load end enable the timer */
    TCNT2 = tcnt2;
    TIMSK2 |= (1<<TOIE2);

    //Configure I/O Pin Directions
    pinMode(FREQ1,    OUTPUT);
    pinMode(FREQ2,    OUTPUT);
    pinMode(FREQ3,    OUTPUT);
    pinMode(FREQ4,    OUTPUT);
    pinMode(FREQ5,    OUTPUT);

}

/* Install the Interrupt Service Routine (ISR) for Timer2.  */
ISR(TIMER2_OVF_vect)
{
    /* Reload the timer */
    TCNT2 = tcnt2;

    count1++; count2++; count3++; count4++; count5++;

    if (count1 == 60)
    {
        digitalWrite(FREQ1, toggle1 == 0 ? HIGH : LOW);
        toggle1 = ~toggle1;
        count1 = 0;
    }
    if (count2 == 53)
    {
        digitalWrite(FREQ2, toggle2 == 0 ? HIGH : LOW);
        toggle2 = ~toggle2;
        count2 = 0;
    }
    if (count3 == 47)
    {
        digitalWrite(FREQ3, toggle3 == 0 ? HIGH : LOW);
        toggle3 = ~toggle3;
        count3 = 0;
    }
    if (count4 == 40)
    {
        digitalWrite(FREQ4, toggle4 == 0 ? HIGH : LOW);
        toggle4 = ~toggle4;
        count4 = 0;
    }
    if (count5 == 35)
    {
        digitalWrite(FREQ5, toggle5 == 0 ? HIGH : LOW);
        toggle5 = ~toggle5;
        count5 = 0;
    }
}

void loop()
{
    //Do whatever else you want to do with your arduino!
}