Looptober24/21FMSynth/21FMSynth.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;

int note = 0;
int gate;
int decay = 128;

float pattern[16];

long unsigned int pattern_inc[4];

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

  cli();

//set timer1 interrupt at 1Hz
  TCCR1A = 0;// set entire TCCR1A register to 0
  TCCR1B = 0;// same for TCCR1B
  TCNT1  = 0;//initialize counter value to 0
  // set compare match register for 1hz increments
  OCR1A = 3905;// = (16*10^6) / (1*1024) - 1 (must be <65536)
  // turn on CTC mode
  TCCR1B |= (1 << WGM12);
  // Set CS10 and CS12 bits for 1024 prescaler
  TCCR1B |= (1 << CS12) | (1 << CS10);  
  // enable timer compare interrupt
  TIMSK1 |= (1 << OCIE1A);

  sei();


  Serial.begin(115200);

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

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

  freq=440;
  phase=0;
  //pattern[0] = 220.0;
  // pattern[1] = 261.6255653005987;
  // pattern[2] = 369.9944227116345;
  // pattern[3] = 391.9954359817495;
  for( int i = 0; i < 16; i++ ) {
    pattern[i] = 440 + i * 80;
  }

  pattern[1] = 0;
  pattern[2] = 0;

  pattern[4] = 0;
  pattern[5] = 0;
 

  for( int i = 0; i < 16; i++ ) {
    pattern_inc[i] = pattern[i] * 975592.231884058;
  }

  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;
  }
}



ISR(TIMER1_COMPA_vect){
  note += 1;
  if( note > 15 ) {
    note = 0;
  }
  phase_inc = pattern_inc[note];
  gate = 4095;
}
 


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