This is the code for the Arduino SPWM inverter for sine wave output. Download the .zip file or copy+paste from below. Read comments in the code!
#include <avr/io.h>
#include <avr/interrupt.h>
// Look up tables with 200 entries each, normalised to have max value of 1600 which is the period of the PWM loaded into register ICR1.
int lookUp1[] = {
50 ,100 ,151 ,201 ,250 ,300 ,349 ,398 ,446 ,494 ,
542 ,589 ,635 ,681 ,726 ,771 ,814 ,857 ,899 ,940 ,
981 ,1020 ,1058 ,1095 ,1131 ,1166 ,1200 ,1233 ,1264 ,1294 ,
1323 ,1351 ,1377 ,1402 ,1426 ,1448 ,1468 ,1488 ,1505 ,1522 ,
1536 ,1550 ,1561 ,1572 ,1580 ,1587 ,1593 ,1597 ,1599 ,1600 ,
1599 ,1597 ,1593 ,1587 ,1580 ,1572 ,1561 ,1550 ,1536 ,1522 ,
1505 ,1488 ,1468 ,1448 ,1426 ,1402 ,1377 ,1351 ,1323 ,1294 ,
1264 ,1233 ,1200 ,1166 ,1131 ,1095 ,1058 ,1020 ,981 ,940 ,
899 ,857 ,814 ,771 ,726 ,681 ,635 ,589 ,542 ,494 ,
446 ,398 ,349 ,300 ,250 ,201 ,151 ,100 ,50 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0};
int lookUp2[] = {
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,
50 ,100 ,151 ,201 ,250 ,300 ,349 ,398 ,446 ,494 ,
542 ,589 ,635 ,681 ,726 ,771 ,814 ,857 ,899 ,940 ,
981 ,1020 ,1058 ,1095 ,1131 ,1166 ,1200 ,1233 ,1264 ,1294 ,
1323 ,1351 ,1377 ,1402 ,1426 ,1448 ,1468 ,1488 ,1505 ,1522 ,
1536 ,1550 ,1561 ,1572 ,1580 ,1587 ,1593 ,1597 ,1599 ,1600 ,
1599 ,1597 ,1593 ,1587 ,1580 ,1572 ,1561 ,1550 ,1536 ,1522 ,
1505 ,1488 ,1468 ,1448 ,1426 ,1402 ,1377 ,1351 ,1323 ,1294 ,
1264 ,1233 ,1200 ,1166 ,1131 ,1095 ,1058 ,1020 ,981 ,940 ,
899 ,857 ,814 ,771 ,726 ,681 ,635 ,589 ,542 ,494 ,
446 ,398 ,349 ,300 ,250 ,201 ,151 ,100 ,50 ,0};
void setup(){
// Register initilisation, see datasheet for more detail.
TCCR1A = 0b10100010;
/*10 clear on match, set at BOTTOM for compA.
10 clear on match, set at BOTTOM for compB.
00
10 WGM1 1:0 for waveform 15.
*/
TCCR1B = 0b00011001;
/*000
11 WGM1 3:2 for waveform 15.
001 no prescale on the counter.
*/
TIMSK1 = 0b00000001;
/*0000000
1 TOV1 Flag interrupt enable.
*/
ICR1 = 1600; // Period for 16MHz crystal, for a switching frequency of 100KHz for 200 subdevisions per 50Hz sin wave cycle.
sei(); // Enable global interrupts.
DDRB = 0b00000110; // Set PB1 and PB2 as outputs.
pinMode(13,OUTPUT);
}
void loop(){; /*Do nothing . . . . forever!*/}
ISR(TIMER1_OVF_vect){
static int num;
// change duty-cycle every period.
OCR1A = lookUp1[num];
OCR1B = lookUp2[num];
if(++num >= 200){ // Pre-increment num then check it's below 200.
num = 0; // Reset num.
}
}