Sine wave from Atmega 328P

[ivconic]

Sine wave from Atmega328P.
And the role of filter.
Showed in pictures:

[ivconic]

/** DDS Sine Generator mit ATMEGS 168
* Timer2 generates the 31250 KHz Clock Interrupt
*
* KHM 2009 / Martin Nawrath
* Kunsthochschule fuer Medien Koeln
* Academy of Media Arts Cologne
*/


#include "avr/pgmspace.h"
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
  
// table of 256 sine values / one sine period / stored in flash memory
PROGMEM const int 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))
 
#define OutputPin 11
int dfreq = 13000;
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(OutputPin, 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
 TWORD();


}
void loop()
{


}


void Setup_timer2() 
//******************************************************************
// timer2 setup
// set prscaler to 1, PWM mode to phase correct PWM, 16000000/510 = 31372.55 Hz clock


{
 
// 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
}


void TWORD()
{
 tword_m=pow(2,32)*dfreq/refclk; // calulate DDS new tuning word
}

[ivconic]

[waltr]

Nice example Ivconic.

The RLC filter does a good job.
I do recommend following the filter with an op-amp to gain and buffer to a low impedance output drive.

I do the same with PIC to produce a sine wave but use a Sallen-Key active filter like this.

[ivconic]

Thanks!

[6666]

Good project thanks

[dbanner]

Cool stuff.