how to vary the voltage of spwm signal

[mobinmk]

hi frnds

i succesfully generated spwm signal by arduino using dds technique, sine look up table, timer, interupt,

then i fed into low pass filter.

now i got sine wave.

i can vary the fequency of sine wave from 1 hz to 1024 hz.

i wana to vary the voltage of sine wave ,in program .

any idea ??

which code will add to my program.

#include "avr/pgmspace.h"

// table of 256 sine values / one sine period / stored in flash memory
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 sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

int ledPin = 13; // LED pin 7
int testPin = 7;
int t2Pin = 6;
byte bb;

double dfreq;
// const double refclk=31372.549; // =16MHz / 510
const double refclk=31376.6; // measured

// variables used inside interrupt service declared as voilatile
volatile byte icnt; // var inside interrupt
volatile byte icnt1; // var inside interrupt
volatile byte c4ms; // counter incremented all 4ms
volatile unsigned long phaccu; // pahse accumulator
volatile unsigned long tword_m; // dds tuning word m

void setup()
{
pinMode(ledPin, OUTPUT); // sets the digital pin as output
Serial.begin(115200); // connect to the serial port
Serial.println("DDS Test");

pinMode(6, OUTPUT); // sets the digital pin as output
pinMode(7, OUTPUT); // sets the digital pin as output
pinMode(11, OUTPUT); // pin11= PWM output / frequency output

Setup_timer2();

// disable interrupts to avoid timing distortion
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) {
if (c4ms > 250) { // timer / wait fou a full second
c4ms=0;
dfreq=analogRead(0); // read Poti on analog pin 0 to adjust output frequency from 0..1023 Hz

cbi (TIMSK2,TOIE2); // disble Timer2 Interrupt
tword_m=pow(2,32)*dfreq/refclk; // calulate DDS new tuning word
sbi (TIMSK2,TOIE2); // enable Timer2 Interrupt

Serial.print(dfreq);
Serial.print(" ");
Serial.println(tword_m);
}

sbi(PORTD,6); // Test / set PORTD,7 high to observe timing with a scope
cbi(PORTD,6); // Test /reset PORTD,7 high to observe timing with a scope
}
}
//******************************************************************
// timer2 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);

sbi (TCCR2A, WGM20); // Mode 1 / Phase Correct PWM
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 ( inclusive push and pop)
ISR(TIMER2_OVF_vect) {

sbi(PORTD,7); // Test / set PORTD,7 high to observe timing with a oscope

phaccu=phaccu+tword_m; // soft DDS, phase accu with 32 bits
icnt=phaccu >> 24; // use upper 8 bits for phase accu as frequency information
// read value fron ROM sine table and send to PWM DAC
OCR2A=pgm_read_byte_near(sine256 + icnt);

if(icnt1++ == 125) { // increment variable c4ms all 4 milliseconds
c4ms++;
icnt1=0;
}

cbi(PORTD,7); // reset PORTD,7
}

 

[chuckey]

To change the output voltage you have to divide the numbers in your look up table by a suitable factor, i.e. 2, to half the output voltage.
I see you are storing the whole of the sinewave, you could store half of it, then phase invert the second half, or store 1/4 of it and , first read the table forward, then back ward, then repeat with the invert. This would give you a better sinewave, though it does depend on your micro being fast enough compared to the wanted output frequency.
Frank

 

[FvM]

I would consider to multiply the table entries with a magnitude factor. Presently the number representation is offset binary (0 = lowest value, 255 highest). To scale symmetrical to zero output voltage, you would e.g. use 2's complement format. Or have a single quadrant table with unsigned numbers only (following chuckey's suggestion) and generate the negative halfwave when calculating the four-quadrant value.

Asking how to write the spwm code is another word for how do I write non-trivial C programs. You need to become familiar with the language and also with number crunching. There are of course "tons" of spwm example codes on the internet. But I believe that it's not really fruitful to use a code that you don't fully understand.

 

[mobinmk]

pls optimize this program,

serial monitor is not working,

i wana to add code for interface lcd with arduino