#include <avr/io.h>
#include <avr/interrupt.h>

#define SinDivisions (400)// Sub divisions of sine wave. 200=10kHz, 260=13kHz 300=15kHz, 360=18kHz, 400=20kHz etc

static int microMHz = 16; // Micro clock frequency
static int freq = 50;     // Sinusoidal frequency
static long int period;   // Period of PWM in clock cycles.
static unsigned int lookUp[SinDivisions];
static char theTCCR1A = 0b10000010; //varible for TCCR1A
volatile double percentMod;

void setup(){
 double temp; //Double varible for <math.h> functions.
 
 period = microMHz*1e6/freq/SinDivisions;// Period of PWM in clock cycles
 
 for(int i = 0; i < SinDivisions/2; i++){ // Generating the look up table.
   temp = sin(i*2*M_PI/SinDivisions)*period;
   lookUp[i] = (int)(temp+0.5);       // Round to integer.    
 }

 // Register initilisation, see datasheet for more detail.
 TCCR1A = theTCCR1A;
 TCCR1B = 0b00011001;
 TIMSK1 = 0b00000001;

 ICR1   = period;   // Period for a switching frequency of 10KHz on a 16MHz crystal with 200 subdivisions per 50Hz sin wave cycle
 sei();             // Enable global interrupts.

 DDRB = 0b00000110; // Set pin 9 and 10 as outputs.

 percentMod = 0;
 for (int i = 0; i < 50; i++) {              // Soft Start (3 seconds)
   percentMod = percentMod + 0.01;
   delay(60);
 }
}

void loop(){;}

ISR(TIMER1_OVF_vect){
   static int num;
   static int delay1;
   static char trig;
   
   if(delay1 == 1){    // Delay by one period because the high time loaded into OCR1A:B values are buffered but can be disconnected immediately by TCCR1A.
     theTCCR1A ^= 0b10100000;// Toggle connect and disconnect of compare output A and B.
     TCCR1A = theTCCR1A;
     delay1 = 0;             // Reset delay1
   } else if(num >= SinDivisions/2){
     num = 0;                // Reset num
     delay1++;
   }
   // change duty-cycle every period.
   OCR1A = OCR1B = int(lookUp[num] * percentMod);
    num++;
}