arduino-modular/waveforms/waveforms.ino

//waveform generator

// hacked from https://www.instructables.com/Arduino-Waveform-Generator-1/

#include <Adafruit_MCP4728.h>
#include <Wire.h>

Adafruit_MCP4728 mcp;

#define nsamp 32
#define dacmax 256

const byte nclk = 200; // a guess
long int freq; //frequency in Hz
long unsigned int phase;
long unsigned int phase_inc;

void setup() {
//  TIMSK0 &= ~_BV(TOIE0); // disable timer0 overflow interrupt

  Serial.begin(115200);

  if (!mcp.begin(0x64)) {
    while (1) {
      delay(100);
    }
  }

//  mcp.setSpeed(400000L);
//  mcp.setSpeed(800000L);
  mcp.setSpeed(800000L);

  freq=440;
  phase=0;
  calc_phase_inc();

  setwave();
}

const float pi=3.14159265;
byte waveform[nsamp];
byte phaseb = 0;
void setwave(){
  for (int isamp=0; isamp<nsamp; ++isamp){
    float phip=(isamp+0.5)/nsamp;
    float phi=2*pi*phip;
    int val=0;

    //saw
  //val = dacmax * isamp / nsamp;
    //val = ( isamp < nsamp / 2 ) ? 0 : dacmax - 1;
        //sine
    val=(sin(phi)+1.0)*dacmax/2;
    //val=((sin(phi)+0.333*sin(3*phi))/0.943+1)*dacmax/2;

    val=max(val,0);
    val=min(val,dacmax-1);
    waveform[isamp]=val;
  }
}


//calculate the phase increment. 
void calc_phase_inc(){
  // by measurement, 2^27 is about 138Hz (C below middle C)
  // 2^27 / 138 = 972592.231884058
  phase_inc = freq * 975592.231884058;
  Serial.println(phase_inc);
}



void loop() {
  phase += phase_inc;
  int redphase = phase >> 27;
  mcp.fastWrite(waveform[redphase] << 4, 0, 0, 0);
}