Minimal VFO using Si5351

SiCrystal.ino

/*
    Simple VFO for a direct conversion receiver.

    Si5351 controlled by a rotary encoder.
    
    Based on code from Paul, VK3HN
    https://github.com/prt459/Arduino_si5351_VFO_Controller_Keyer

*/

const unsigned long int FREQ_DEFAULT = 7100000ULL;

#define ENCODER_A 3 // DT
#define ENCODER_B 2 // CLK

#include <RotaryEncoder.h>   // by Maattias Hertel http://www.mathertel.de/Arduino/RotaryEncoderLibrary.aspx
#include <si5351.h>     // Etherkit Si3531 library Jason Mildrum,  V2.1.4  
                      // https://github.com/etherkit/Si5351Arduino
#include <Wire.h>       // built in
Si5351 si5351;                // I2C address defaults to x60 in the NT7S lib
RotaryEncoder gEncoder = RotaryEncoder(ENCODER_A, ENCODER_B, RotaryEncoder::LatchMode::FOUR3);
long gEncoderPosition = 0;

unsigned long int gFrequency = FREQ_DEFAULT;
unsigned long int gStep = 100;

void setup() {
  Serial.begin(115200);
  Wire.begin();
  gFrequency = FREQ_DEFAULT;
  setupOscillator();
  setupRotaryEncoder();
  delay(500);
  si5351.set_freq(FREQ_DEFAULT * SI5351_FREQ_MULT, SI5351_CLK0);
  si5351.output_enable(SI5351_CLK0, 1);
}

void loop() {
  // check for change in the rotary encoder
  gEncoder.tick();
  long newEncoderPosition = gEncoder.getPosition();
  if(newEncoderPosition != gEncoderPosition) {
    long encoderDifference = newEncoderPosition - gEncoderPosition;
    gEncoderPosition = newEncoderPosition;
    Serial.println(encoderDifference);
    frequencyAdjust(encoderDifference);
  }
}

void setupRotaryEncoder() {
  attachInterrupt(digitalPinToInterrupt(ENCODER_A), checkPosition, CHANGE);
  attachInterrupt(digitalPinToInterrupt(ENCODER_B), checkPosition, CHANGE);
}

// This interrupt routine will be called on any change of one of the input signals
void checkPosition() {
  gEncoder.tick(); // just call tick() to check the state.
}

void frequencyAdjust(int delta) {
  Serial.print("Adjust: ");
  Serial.println(delta);
  gFrequency += (delta * gStep);
  setVfoFrequency(gFrequency);
}

void setVfoFrequency(unsigned long int frequency) {
  si5351.set_freq(frequency * SI5351_FREQ_MULT, SI5351_CLK0); //  
  Serial.print("set frequency: ");
  Serial.println(frequency);
}

void setupOscillator() {
  bool i2c_found = si5351.init(SI5351_CRYSTAL_LOAD_8PF, 0, 0);
  Serial.print("si5351: ");
  Serial.println(i2c_found ? "Found" : "Missing");
  si5351.set_correction(135000, SI5351_PLL_INPUT_XO);    // Library update 26/4/2020: requires destination register address  ... si5351.set_correction(19100, SI5351_PLL_INPUT_XO);
  si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLA);
  si5351.set_freq(500000000ULL, SI5351_CLK0);
  si5351.drive_strength(SI5351_CLK0, SI5351_DRIVE_4MA); 
  si5351.output_enable(SI5351_CLK0, 1);  // turn VFO on 
}