Arduino signal generator

[kEhYo77]

This code should work on Mega but you have to change the OUTPUT pin numbers to 11 and 12 as 16bit counter Timer1 [/size]is assigned there differently.
I will improve on that code to make it work with an LCD/serial and a rotary encoder to automatically dial in desired frequency.
Another weekend off
This one is fresh from the bakery and if someone wants to modify it feel free.

[madddann]

OMG kEhYo77, I'm speechless, thank you soo much, I saw this just now.

TK, thanks for testing.

Dann

[kEhYo77]

I came across this variable frequency! 3 phase! sine! generator code for Arduino UNO, hope you like it.

// 3 phase PWM sine
// (c) 2016 C. Masenas
// Modified from original DDS from:
// KHM 2009 /  Martin Nawrath


// table of 256 sine values / one sine period / stored in flash memory
PROGMEM const unsigned char 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 testPin = 7;
int enablePin = 6 ;


volatile  float freq=1;
const float refclk=122.549  ;     //  16 MHz/510/256


// variables used inside interrupt service declared as voilatile
volatile unsigned long sigma;   // phase accumulator
volatile unsigned long delta;  // phase increment
byte phase0, phase1, phase2 ;


void setup()
{
  Serial.begin(9600);        // connect to the serial port
  Serial.println("DDS Test");


  pinMode(enablePin, OUTPUT);      // sets the digital pin as output
  pinMode(testPin, OUTPUT);      // sets the digital pin as output
  pinMode(9, OUTPUT);     // pin9= PWM  output / frequency output
  pinMode(10, OUTPUT);     // pin10= PWM  output / frequency output
  pinMode(11, OUTPUT);     // pin11= PWM  output / frequency output


  Setup_timer2();
  Setup_timer1();
  digitalWrite(enablePin, HIGH);


// the waveform index is the highest 8 bits of sigma
// choose refclk as freq to increment the lsb of the 8 highest bits
//    for every call to the ISR of timer2 overflow
// the lsb of the 8 highest bits is 1<<24 (1LL<<24 for long integer literal)
  delta = (1LL<<24)*freq/refclk ; 
}
void loop(){
 
  changeFreq(20);
  delay(10000);
  changeFreq(25);
  delay(10000);
             
}


void changeFreq(float _freq){
  cbi (TIMSK2,TOIE2);              // disable timer2 overflow detect
  freq = _freq;
  delta=(1LL<<24)*freq/refclk;  // update phase increment
  sbi (TIMSK2,TOIE2);              // enable timer2 overflow detect
}


//******************************************************************
// timer2 setup
// set prscaler to 1,  fast PWM
void Setup_timer2() {


// Timer2 Clock Prescaler to : 1
  sbi (TCCR2B, CS20);  // set
  cbi (TCCR2B, CS21);  // clear
  cbi (TCCR2B, CS22);


  // Timer2 PWM Mode
  cbi (TCCR2A, COM2A0);  // clear OC2A on Compare Match, PWM pin 11
  sbi (TCCR2A, COM2A1);


  // set to fast PWM
  sbi (TCCR2A, WGM20);  // Mode 1, phase correct PWM
  cbi (TCCR2A, WGM21);
  cbi (TCCR2B, WGM22);


  sbi (TIMSK2,TOIE2);              // enable overflow detect
 
}
// timer1 setup  (sets pins 9 and 10)
// set prscaler to 1, PWM mode to phase correct PWM,  16000000/510 = 31372.55 Hz clock
void Setup_timer1() {


// 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);  // clear OC1A on Compare Match, PWM pin 9
  sbi (TCCR1A, COM1A1);
  cbi (TCCR1A, COM1B0);  // clear OC1B on Compare Match, PWM pin 10
  sbi (TCCR1A, COM1B1);


  sbi (TCCR1A, WGM10);  // Mode 1  / phase correct PWM
  cbi (TCCR1A, WGM11);
  cbi (TCCR1B, WGM12);
  cbi (TCCR1B, WGM13);
}


//******************************************************************
// Timer2 Interrupt Service at 31372,550 KHz = 32uSec
// this is the timebase REFCLOCK for the DDS generator
// runtime : 8 microseconds ( inclusive push and pop)
// OC2A - pin 11
// OC1B - pin 10
// OC1A - pin 9
// https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM
ISR(TIMER2_OVF_vect) {


  sbi(PORTD,testPin);         


  sigma=sigma+delta; // soft DDS, phase accu with 32 bits
  phase0=sigma >> 24;     // use upper 8 bits for phase accu as frequency information
                         // read value fron ROM sine table and send to PWM DAC
  phase1 = phase0 +85 ;
  phase2 = phase0 +170 ;


  OCR2A=pgm_read_byte_near(sine256 + phase0);  // pwm pin 11
  OCR1B=pgm_read_byte_near(sine256 + phase1);  // pwm pin 10
  OCR1A=pgm_read_byte_near(sine256 + phase2);  // pwm pin 9


  cbi(PORTD,testPin);           
 
}

[Reiyuki]

Great thread, everyone.


One issue I and others have run into is clock-rate.  At higher frequencies, many of the sketches posted lose granularity and become distorted.

Most Arduino run at 16mhz, but sketches using PWM or pulses are often only clean up to 50-200khz.

I've had good luck boosting this number by using higher clockrate Arduinos, specifically Teensy's:
https://www.pjrc.com/teensy/

The improvements are largely linear (sketches that become distorted at 100khz with 16mhz clock tend to reach 300khz with 48mhz clock.

Note: Some sketches (especially ones using interrupts) will need to be tweaked to work with the different chipset.  Also, many of the faster Teensy's are 3.3v and not 5v, so you may need to make changes elsewhere to accommodate.