I'm using an AVR Mega 168 to generate a sine wave via pulse width modulation. My goal is to generate a sine wave with a frequency of approximately 50 Hz. I understand that the PWM frequency needs to be as fast possible so its easier to attenuate in the filter.
So far, my µC is running at 8 MHz using the internal RC oscillator (I plan on moving to a crystal later on - taking this one step a time). This provides me with a maximum PWM base frequency of 8x106/256 (fast PWM mode) = 31.25 kHz.
My program updates the duty cycle whenever timer0 overflows i.e. every 32 µS (I think... since 1/31250 = 32 µS).
My question now is, how can I 'control' the frequency of the actual sine wave? I can easily slow down by prescaling but that would obviously make the base frequency quite low.
I have included my code below:
uint8_t i=0; int main(void) { int ipwm; DDRD = 0xFF; TCCR0A = 0b10000011; TCCR0B = (1 << WGM12); TIMSK0 |= (1 << TOIE0); TIFR1 |= (1 << OCF0A); TCCR0B = (1 << CS10); TCNT0 = 0; OCR0A = 128; sei(); for(;;) { } return 1; } ISR(TIMER0_OVF_vect) { OCR0A=pgm_read_byte(&sinewave[i]); // update duty cycle i++; } 
