Hi
I just completed a project of mine that generates 3 Sine waves 120 degrees out of phase. It took my hours to understand how to generate the sine tables and so forth. Thus I commented in as much detail as possible for future programmers to understand and grasp the idea quicker.
Code:
/*
*
* DDS Sine Generator mit ATMEGS 328
* Timer2 generates the 31250 KHz Clock Interrupt
* Use Timer2 Interrupt to change duty cycle for the output PWM signals
* D. Tolken
* 120 degress out of phase signals for 3 phase BLDC motor controller
* CPUT, South Africa
a Huge thumbs up and thanks must be given to Martin Nawrath for the developement of the original code to generate a sine wave using PWM and a LPF.
Link:
http://interface.khm.de/index.php/lab/experiments/arduino-dds-sinewave-generator/
*/
#include "avr/pgmspace.h" //Store data in flash (program) memory instead of SRAM
// Look Up table of a single sine period divied up into 256 values. Refer to PWM to sine.xls on how the values was calculated
PROGMEM prog_uchar sine256[] = {
127,130,133,136,139,143,146,149,152,155,158,161,164,167,170,173,176,178,181,184,187,190,192,195,198,200,203,205,208,210,212,215,217,219,221,223,225,227,229,231,233,234,236,238,239,240,
242,243,244,245,247,248,249,249,250,251,252,252,253,253,253,254,254,254,254,254,254,254,253,253,253,252,252,251,250,249,249,248,247,245,244,243,242,240,239,238,236,234,233,231,229,227,225,223,
221,219,217,215,212,210,208,205,203,200,198,195,192,190,187,184,181,178,176,173,170,167,164,161,158,155,152,149,146,143,139,136,133,130,127,124,121,118,115,111,108,105,102,99,96,93,90,87,84,81,78,
76,73,70,67,64,62,59,56,54,51,49,46,44,42,39,37,35,33,31,29,27,25,23,21,20,18,16,15,14,12,11,10,9,7,6,5,5,4,3,2,2,1,1,1,0,0,0,0,0,0,0,1,1,1,2,2,3,4,5,5,6,7,9,10,11,12,14,15,16,18,20,21,23,25,27,29,31,
33,35,37,39,42,44,46,49,51,54,56,59,62,64,67,70,73,76,78,81,84,87,90,93,96,99,102,105,108,111,115,118,121,124
};
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit)) //define a bit to have the properties of a clear bit operator
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))//define a bit to have the properties of a set bit operator
int PWM1= 11;// PWM1 output, phase 1
int PWM2 = 3; //[WM2 ouput, phase 2
int PWM3 = 10; //PWM3 output, phase 3
int offset_1 = 85; //offset 1 is 120 degrees out of phase with previous phase, Refer to PWM to sine.xls
int offset_2 = 170; //offset 2 is 120 degrees out of phase with offset 1. Refer to PWM to sine.xls
int program_exec_time = 6; //monitor how quickly the interrupt trigger
int ISR_exec_time = 7; //monitor how long the interrupt takes
double dfreq;
const double refclk=31376.6; // measured output frequency
// variables used inside interrupt service declared as voilatile
volatile byte current_count; // Keep track of where the current count is in sine 256 array
volatile byte ms4_delay; //variable used to generate a 4ms delay
volatile byte c4ms; // after every 4ms this variable is incremented, its used to create a delay of 1 second
volatile unsigned long phase_accumulator; // pahse accumulator
volatile unsigned long tword_m; // dds tuning word m, refer to DDS_calculator (from Martin Nawrath) for explination.
void setup()
{
pinMode(PWM1, OUTPUT); //sets the digital pin as output
pinMode(PWM2, OUTPUT); //sets the digital pin as output
pinMode(PWM3, OUTPUT); //sets the digital pin as output
pinMode(program_exec_time, OUTPUT); //sets the digital pin as output
pinMode(9, OUTPUT); //sets the digital pin as output
sbi(PORTD,program_exec_time); //Sets the pin
Setup_timer1();
Setup_timer2();
//Disable Timer 1 interrupt to avoid any timing delays
cbi (TIMSK0,TOIE0); //disable Timer0 !!! delay() is now not available
sbi (TIMSK2,TOIE2); //enable Timer2 Interrupt
dfreq=1000.0; //initial output frequency = 1000.o Hz
tword_m=pow(2,32)*dfreq/refclk; //calulate DDS new tuning word
}
void loop()
{
while(1)
{
sbi(PORTD,program_exec_time); //Sets the pin
if (c4ms > 250) // c4ms = 4ms, thus 4ms *250 = 1 second delay
{
c4ms=0; //Reset c4ms
dfreq=analogRead(0); //Read voltage on analog 1 to see desired output frequency, 0V = 0Hz, 5V = 1.023kHz
cbi (TIMSK2,TOIE2); //Disable Timer2 Interrupt
tword_m=pow(2,32)*dfreq/refclk; //Calulate DDS new tuning word
sbi (TIMSK2,TOIE2); //Enable Timer2 Interrupt
}
}
}
//Timer 1 setup
//Set prscaler to 1, PWM mode to phase correct PWM, 16000000/510 = 31372.55 Hz clock
void Setup_timer1(void)
{
// Timer1 Clock Prescaler to : 1
sbi (TCCR1B, CS10);
cbi (TCCR1B, CS11);
cbi (TCCR1B, CS12);
// Timer1 PWM Mode set to Phase Correct PWM
cbi (TCCR1A, COM1A0);
sbi (TCCR1A, COM1A1);
cbi (TCCR1A, COM1B0);
sbi (TCCR1A, COM1B1);
// Mode 1 / Phase Correct PWM
sbi (TCCR1A, WGM10);
cbi (TCCR1A, WGM11);
cbi (TCCR1B, WGM12);
cbi (TCCR1B, WGM13);
}
//Timer 1 setup
//Set prscaler to 1, PWM mode to phase correct PWM, 16000000/510 = 31372.55 Hz clock
void Setup_timer2()
{
// Timer2 Clock Prescaler to : 1
sbi (TCCR2B, CS20);
cbi (TCCR2B, CS21);
cbi (TCCR2B, CS22);
// Timer2 PWM Mode set to Phase Correct PWM
cbi (TCCR2A, COM2A0); // clear Compare Match
sbi (TCCR2A, COM2A1);
cbi (TCCR2A, COM2B0);
sbi (TCCR2A, COM2B1);
// Mode 1 / Phase Correct PWM
sbi (TCCR2A, WGM20);
cbi (TCCR2A, WGM21);
cbi (TCCR2B, WGM22);
}
//Timer2 Interrupt Service at 31372,550 KHz = 32uSec
//This is the timebase REFCLOCK for the DDS generator
//FOUT = (M (REFCLK)) / (2 exp 32)
//Runtime : 8 microseconds
ISR(TIMER2_OVF_vect)
{
cbi(PORTD,program_exec_time); //Clear the pin
sbi(PORTD,ISR_exec_time); // Sets the pin
phase_accumulator=phase_accumulator+tword_m; //Adds tuning M word to previoud phase accumulator. refer to DDS_calculator (from Martin Nawrath) for explination.
current_count=phase_accumulator >> 24; // use upper 8 bits of phase_accumulator as frequency information
OCR2A=pgm_read_byte_near(sine256 + current_count); // read value fron ROM sine table and send to PWM
OCR2B=pgm_read_byte_near(sine256 + (uint8_t)(current_count + offset_1)); // read value fron ROM sine table and send to PWM, 120 Degree out of phase of PWM1
OCR1A = pgm_read_byte_near(sine256 + (uint8_t)(current_count + offset_2));// read value fron ROM sine table and send to PWM, 120 Degree out of phase of PWM2
OCR1B = pgm_read_byte_near(sine256 + (uint8_t)(current_count + offset_2));// read value fron ROM sine table and send to PWM, 120 Degree out of phase of PWM2
//increment variable ms4_delay every 4mS/125 = milliseconds 32uS
if(ms4_delay++ == 125)
{
c4ms++;
ms4_delay=0; //reset count
}
cbi(PORTD,ISR_exec_time); //Clear the pin
}
Sine wave table calculater: PWM to sine.xlsx
DDS Frequency Calc (Not My Document, helps to explain): dds_calc.xls
Circuit Diagram (Fritz): Breadboard
Measured Results: Output.bmp
Feel free to comment/ask questions
Cheers 
dds_calc.xls (8 KB)
PWM to sine.xlsx (44 KB)
Breadboard.fzz (13.9 KB)
Output.BMP (219 KB)
