Features
Setup
Schematics / wiring
In operation video
Double Conversion Receiver
Instructions
Note about User Preferences
About the Rotary Encoder used in this project
The sale of this VFO already assembled
Disclaimer

Published February 28, 2021 © GPL3+

10kHz to 225MHz VFO/RF Generator with Si5351 - Version 2

For use in DIY homebrew radio equipment such superheterodyne single/double conversion receiver, SDR, HAM QRP transceivers or RF generator.

IntermediateWork in progress104,556

10kHz to 225MHz VFO/RF Generator with Si5351 - Version 2

Things used in this project

Hardware components

Breadboard (generic)

Arduino Nano R3

Rotary Encoder with Push-Button

Adafruit SSD1306 128X64 OLED DISPLAY

Adafruit SI5351 CLOCK GEN MODULE

Toggle Switch, SPDT

Panasonic RCA JACK FOR RF OUTPUT CONECTION

Capacitor 100 nF

Capacitor 10 µF

Capacitor 10 nF

Resistor 1k ohm

Inductor 100 uH

Software apps and online services

Arduino IDE

Story

This is a project of a VFO (variable frequency oscillator) for use in DIY homebrew radio equipement such as Superheterodyne Single / Double Conversion Receivers, DCR, SDR or Ham QRP Transceivers. It has a Bargraph indicator for Signal Strenght (S-Meter) and 20 Band presets. Can be used as RF/Clock generator too. This is the new version (V.2), I updated the previous project and it includes new features.

Features:

Operation range from 10kHz to 225MHz.
Tuning steps of 1Hz, 10Hz, 1kHz, 5kHz, 10kHz and 1MHz.
Intermediate Frequency (IF) offset (+ or -) adjustable.
20 Band Presets (shortcuts) to the BCB and HAM frequencies.
Generator funcion mode.
RX / TX Mode Selector for use in Homebrew QRP Transceivers.
Bargraph for Signal Meter through the analog input (ADC).
For use as Local Oscillator on Homebrew radio receivers such as Superheterodyne, SDR, Direct Conversion and Homebrew QRP Transceivers.
For use in Double Conversion / Air Band Superhet Receivers in conjunction with Si4735 or Si4732 DSP radio chip.
For use as a simple RF/Clock generator for calibration reference or clock generation.
Works with Arduino Uno, Nano and Pro Mini.
Uses a common 128x64 I2C OLED SSD1306 display and Si5351 module.
I2C data transfer, only 2 wires to connect the display / Si5351 and arduino.
High stability and precision for frequency generation.
Simple yet very efficient and free.
Update Jun, 2022: added an Alternative Version with support to bigger OLED SH1106 1.3" display and CW Keying input, see more details on text.

Setup:

1 / 4

Schematics / wiring:

An old VFO from the 1960s. The Great-Grandfather of the VFO DDS:

An old VFO from the 1960s

In operation video:

My VFO project being successfully used around the world :-)

Tests with oscilloscope showing waveforms.

VFO operating as a local oscillator in a Superheteridyne receiver.

Double Conversion Receiver:

For anyone interested in making a double conversion receiver with the SI5351 and SI4735(32), this is the block diagram of the receiver blocks that I built and it works great. Using JCR 10kHz-225MHz VFO. The mixer is the popular NE602 / SA612 IC.

Instructions:

Open the scketch on Arduino IDE, install all the required libraries.
Choose the preferences (see note) and compile the sketch and then load it to the Arduino Nano, Uno or Pro Mini.
Follow the schematics to wire the Arduino, Display, Si5351 module, rotary encoder, etc.
Power up the Arduino.
Rotate the rotary encoder to tune up or down the frequency.
Push the push button 1 to change the frequency step tuning. The steps available are 1Hz, 10Hz, 1kHz, 5kHz, 10kHz and 1MHz.
Push the push button 2 to browse (select) the 20 band presets or enter the generator mode.
Turn on/off the switch SW 2 to change from RX to TX mode. RX mode = SW 2 Open and TX mode = SW 2 Closed to GND. When in TX mode, the IF value is not added/sub from the RF out. This is ideal for use in Homebrew QRP Transceivers.
Connect the S-Meter output signal from your radio to the X2 connector (S-Meter input). This input has adjustable sensitivity, the gain must be adjusted in Sketch, accepting signals from 500mV to 5V (max).
Known Issue: if it freezes in the initialization text, comment (put a //) at the line 77 statup_text ();

Note about User Preferences:

-It is possible to change the followings items on sketch:

#define IF 455 //Enter your IF frequency, ex: 455 = 455kHz, 10700 = 10.7MHz, 0 = to direct convert receiver or RF generator, + will add and - will subtract IF offfset.

#define BAND_INIT 7 //Enter your initial Band (1-21) at startup, ex: 1 = Freq Generator, 2 = 800kHz (MW), 7 = 7.2MHz (40m), 11 = 14.1MHz (20m).

#define XT_CAL_F 33000 //Si5351 calibration factor, adjust to get exatcly 10MHz. Increasing this value will decreases the frequency and vice versa.

#define S_GAIN 303 //Adjust the sensitivity of Signal Meter A/D input: 101 = 500mv; 202 = 1v; 303 = 1.5v; 404 = 2v; 505 = 2.5v; 1010 = 5v (max).

#define tunestep A0 //The pin used by tune step push button.

#define band A1 //The pin used by band selector push button.

#define rx_tx A2 //The pin used by RX / TX selector switch, RX = switch open, TX = switch closed to GND. When in TX, the IF is not considered.

#define adc A3 //The pin used by Signal Meter A/D input.

About the Rotary Encoder used in this project:

I used the low-cost EC11 - 15mm rotary encoder (photo below), which can be purchased on Aliexpress in batches of 5 units. Note that this encoder has a blue plastic base and has 5 pins, 3 for the encoder and 2 for the push switch. This worked perfectly with the project. If the encoder action is inverted (it decreases when turning clockwise), simply flip (invert) the connection of the pins that go to D2 and D3. There are other types of encoders, some come with a built-in board, which can be tested here, but I have not tested them. In some cases, it may be necessary to include 2x 10k OHMM pullup resistors between +5v and pins D2 and D3.

EC11 - Rotary Encoder used in this project.

The sale of this VFO already assembled:

This project is being sold on eBay and Aliexpress as a CLONE, already assembled including internal rechargeable battery. In case anyone is interested, this is the picture of it.

Disclaimer: The author of this project has no connection or any responsability with the sale of this assembled product. This product is not a complete radio transceiver, as described in the sales ad, it works only as a VFO / Continuous RF Generator.

Disclaimer:

The author of this project has no responsibility for the products (clones) being traded via China, as the manufacture and sale of these products has no connection with the author. This project is open source and is not intended for commercial profit.
The author of this project reserves the right to change, modify or do corrections to the hardware and/or software at any time without notice or obligation to persons who already assembled it.
Don't expect this project to perform as well or better than professional and commercial equipments, this is an amateur DIY home project that aims at the personal satisfaction of setting up at home and seeing it work beyond the learning that this activity provides.

Julio Cesar - CesarSound - ver 2.0 - Feb/2021.

Code

Sketch SI5351_VFO_RF_GEN_OLED_JCR_V2

/**********************************************************************************************************
  10kHz to 225MHz VFO / RF Generator with Si5351 and Arduino Nano, with Intermediate Frequency (IF) offset
  (+ or -), RX/TX Selector for QRP Transceivers, Band Presets and Bargraph S-Meter. See the schematics for
  wiring and README.txt for details. By J. CesarSound - ver 2.0 - Feb/2021.
***********************************************************************************************************/

//Libraries
#include <Wire.h>                 //IDE Standard
#include <Rotary.h>               //Ben Buxton https://github.com/brianlow/Rotary
#include <si5351.h>               //Etherkit https://github.com/etherkit/Si5351Arduino
#include <Adafruit_GFX.h>         //Adafruit GFX https://github.com/adafruit/Adafruit-GFX-Library
#include <Adafruit_SSD1306.h>     //Adafruit SSD1306 https://github.com/adafruit/Adafruit_SSD1306

//User preferences
//------------------------------------------------------------------------------------------------------------
#define IF         455       //Enter your IF frequency, ex: 455 = 455kHz, 10700 = 10.7MHz, 0 = to direct convert receiver or RF generator, + will add and - will subtract IF offfset.
#define BAND_INIT  7         //Enter your initial Band (1-21) at startup, ex: 1 = Freq Generator, 2 = 800kHz (MW), 7 = 7.2MHz (40m), 11 = 14.1MHz (20m). 
#define XT_CAL_F   33000     //Si5351 calibration factor, adjust to get exatcly 10MHz. Increasing this value will decreases the frequency and vice versa.
#define S_GAIN     303       //Adjust the sensitivity of Signal Meter A/D input: 101 = 500mv; 202 = 1v; 303 = 1.5v; 404 = 2v; 505 = 2.5v; 1010 = 5v (max).
#define tunestep   A0        //The pin used by tune step push button.
#define band       A1        //The pin used by band selector push button.
#define rx_tx      A2        //The pin used by RX / TX selector switch, RX = switch open, TX = switch closed to GND. When in TX, the IF value is not considered.
#define adc        A3        //The pin used by Signal Meter A/D input.
//------------------------------------------------------------------------------------------------------------

Rotary r = Rotary(2, 3);
Adafruit_SSD1306 display = Adafruit_SSD1306(128, 64, &Wire);
Si5351 si5351(0x60); //Si5351 I2C Address 0x60

unsigned long freq, freqold, fstep;
long interfreq = IF, interfreqold = 0;
long cal = XT_CAL_F;
unsigned int smval;
byte encoder = 1;
byte stp, n = 1;
byte count, x, xo;
bool sts = 0;
unsigned int period = 100;
unsigned long time_now = 0;

ISR(PCINT2_vect) {
  char result = r.process();
  if (result == DIR_CW) set_frequency(1);
  else if (result == DIR_CCW) set_frequency(-1);
}

void set_frequency(short dir) {
  if (encoder == 1) {                         //Up/Down frequency
    if (dir == 1) freq = freq + fstep;
    if (freq >= 225000000) freq = 225000000;
    if (dir == -1) freq = freq - fstep;
    if (fstep == 1000000 && freq <= 1000000) freq = 1000000;
    else if (freq < 10000) freq = 10000;
  }
  if (encoder == 1) {                       //Up/Down graph tune pointer
    if (dir == 1) n = n + 1;
    if (n > 42) n = 1;
    if (dir == -1) n = n - 1;
    if (n < 1) n = 42;
  }
}

void setup() {
  Wire.begin();
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextColor(WHITE);
  display.display();

  pinMode(2, INPUT_PULLUP);
  pinMode(3, INPUT_PULLUP);
  pinMode(tunestep, INPUT_PULLUP);
  pinMode(band, INPUT_PULLUP);
  pinMode(rx_tx, INPUT_PULLUP);

  //statup_text();  //If you hang on startup, comment

  si5351.init(SI5351_CRYSTAL_LOAD_8PF, 0, 0);
  si5351.set_correction(cal, SI5351_PLL_INPUT_XO);
  si5351.drive_strength(SI5351_CLK0, SI5351_DRIVE_8MA);
  si5351.output_enable(SI5351_CLK0, 1);                  //1 - Enable / 0 - Disable CLK
  si5351.output_enable(SI5351_CLK1, 0);
  si5351.output_enable(SI5351_CLK2, 0);

  PCICR |= (1 << PCIE2);
  PCMSK2 |= (1 << PCINT18) | (1 << PCINT19);
  sei();

  count = BAND_INIT;
  bandpresets();
  stp = 4;
  setstep();
}

void loop() {
  if (freqold != freq) {
    time_now = millis();
    tunegen();
    freqold = freq;
  }

  if (interfreqold != interfreq) {
    time_now = millis();
    tunegen();
    interfreqold = interfreq;
  }

  if (xo != x) {
    time_now = millis();
    xo = x;
  }

  if (digitalRead(tunestep) == LOW) {
    time_now = (millis() + 300);
    setstep();
    delay(300);
  }

  if (digitalRead(band) == LOW) {
    time_now = (millis() + 300);
    inc_preset();
    delay(300);
  }

  if (digitalRead(rx_tx) == LOW) {
    time_now = (millis() + 300);
    sts = 1;
  } else sts = 0;

  if ((time_now + period) > millis()) {
    displayfreq();
    layout();
  }
  sgnalread();
}

void tunegen() {
  si5351.set_freq((freq + (interfreq * 1000ULL)) * 100ULL, SI5351_CLK0);
}

void displayfreq() {
  unsigned int m = freq / 1000000;
  unsigned int k = (freq % 1000000) / 1000;
  unsigned int h = (freq % 1000) / 1;

  display.clearDisplay();
  display.setTextSize(2);

  char buffer[15] = "";
  if (m < 1) {
    display.setCursor(41, 1); sprintf(buffer, "%003d.%003d", k, h);
  }
  else if (m < 100) {
    display.setCursor(5, 1); sprintf(buffer, "%2d.%003d.%003d", m, k, h);
  }
  else if (m >= 100) {
    unsigned int h = (freq % 1000) / 10;
    display.setCursor(5, 1); sprintf(buffer, "%2d.%003d.%02d", m, k, h);
  }
  display.print(buffer);
}

void setstep() {
  switch (stp) {
    case 1: stp = 2; fstep = 1; break;
    case 2: stp = 3; fstep = 10; break;
    case 3: stp = 4; fstep = 1000; break;
    case 4: stp = 5; fstep = 5000; break;
    case 5: stp = 6; fstep = 10000; break;
    case 6: stp = 1; fstep = 1000000; break;
  }
}

void inc_preset() {
  count++;
  if (count > 21) count = 1;
  bandpresets();
  delay(50);
}

void bandpresets() {
  switch (count)  {
    case 1: freq = 100000; tunegen(); break;
    case 2: freq = 800000; break;
    case 3: freq = 1800000; break;
    case 4: freq = 3650000; break;
    case 5: freq = 4985000; break;
    case 6: freq = 6180000; break;
    case 7: freq = 7200000; break;
    case 8: freq = 10000000; break;
    case 9: freq = 11780000; break;
    case 10: freq = 13630000; break;
    case 11: freq = 14100000; break;
    case 12: freq = 15000000; break;
    case 13: freq = 17655000; break;
    case 14: freq = 21525000; break;
    case 15: freq = 27015000; break;
    case 16: freq = 28400000; break;
    case 17: freq = 50000000; break;
    case 18: freq = 100000000; break;
    case 19: freq = 130000000; break;
    case 20: freq = 144000000; break;
    case 21: freq = 220000000; break;
  }
  si5351.pll_reset(SI5351_PLLA);
  stp = 4; setstep();
}

void layout() {
  display.setTextColor(WHITE);
  display.drawLine(0, 20, 127, 20, WHITE);
  display.drawLine(0, 43, 127, 43, WHITE);
  display.drawLine(105, 24, 105, 39, WHITE);
  display.drawLine(87, 24, 87, 39, WHITE);
  display.drawLine(87, 48, 87, 63, WHITE);
  display.drawLine(15, 55, 82, 55, WHITE);
  display.setTextSize(1);
  display.setCursor(59, 23);
  display.print("STEP");
  display.setCursor(54, 33);
  if (stp == 2) display.print("  1Hz"); if (stp == 3) display.print(" 10Hz"); if (stp == 4) display.print(" 1kHz");
  if (stp == 5) display.print(" 5kHz"); if (stp == 6) display.print("10kHz"); if (stp == 1) display.print(" 1MHz");
  display.setTextSize(1);
  display.setCursor(92, 48);
  display.print("IF:");
  display.setCursor(92, 57);
  display.print(interfreq);
  display.print("k");
  display.setTextSize(1);
  display.setCursor(110, 23);
  if (freq < 1000000) display.print("kHz");
  if (freq >= 1000000) display.print("MHz");
  display.setCursor(110, 33);
  if (interfreq == 0) display.print("VFO");
  if (interfreq != 0) display.print("L O");
  display.setCursor(91, 28);
  if (!sts) display.print("RX"); if (!sts) interfreq = IF;
  if (sts) display.print("TX"); if (sts) interfreq = 0;
  bandlist(); drawbargraph();
  display.display();
}

void bandlist() {
  display.setTextSize(2);
  display.setCursor(0, 25);
  if (count == 1) display.print("GEN"); if (count == 2) display.print("MW"); if (count == 3) display.print("160m"); if (count == 4) display.print("80m");
  if (count == 5) display.print("60m"); if (count == 6) display.print("49m"); if (count == 7) display.print("40m"); if (count == 8) display.print("31m");
  if (count == 9) display.print("25m"); if (count == 10) display.print("22m"); if (count == 11) display.print("20m"); if (count == 12) display.print("19m");
  if (count == 13) display.print("16m"); if (count == 14) display.print("13m"); if (count == 15) display.print("11m"); if (count == 16) display.print("10m");
  if (count == 17) display.print("6m"); if (count == 18) display.print("WFM"); if (count == 19) display.print("AIR"); if (count == 20) display.print("2m");
  if (count == 21) display.print("1m");
  if (count == 1) interfreq = 0; else if (!sts) interfreq = IF;
}

void sgnalread() {
  smval = analogRead(adc); x = map(smval, 0, S_GAIN, 1, 14); if (x > 14) x = 14;
}

void drawbargraph() {
  byte y = map(n, 1, 42, 1, 14);
  display.setTextSize(1);

  //Pointer
  display.setCursor(0, 48); display.print("TU");
  switch (y) {
    case 1: display.fillRect(15, 48, 2, 6, WHITE); break;
    case 2: display.fillRect(20, 48, 2, 6, WHITE); break;
    case 3: display.fillRect(25, 48, 2, 6, WHITE); break;
    case 4: display.fillRect(30, 48, 2, 6, WHITE); break;
    case 5: display.fillRect(35, 48, 2, 6, WHITE); break;
    case 6: display.fillRect(40, 48, 2, 6, WHITE); break;
    case 7: display.fillRect(45, 48, 2, 6, WHITE); break;
    case 8: display.fillRect(50, 48, 2, 6, WHITE); break;
    case 9: display.fillRect(55, 48, 2, 6, WHITE); break;
    case 10: display.fillRect(60, 48, 2, 6, WHITE); break;
    case 11: display.fillRect(65, 48, 2, 6, WHITE); break;
    case 12: display.fillRect(70, 48, 2, 6, WHITE); break;
    case 13: display.fillRect(75, 48, 2, 6, WHITE); break;
    case 14: display.fillRect(80, 48, 2, 6, WHITE); break;
  }

  //Bargraph
  display.setCursor(0, 57); display.print("SM");
  switch (x) {
    case 14: display.fillRect(80, 58, 2, 6, WHITE);
    case 13: display.fillRect(75, 58, 2, 6, WHITE);
    case 12: display.fillRect(70, 58, 2, 6, WHITE);
    case 11: display.fillRect(65, 58, 2, 6, WHITE);
    case 10: display.fillRect(60, 58, 2, 6, WHITE);
    case 9: display.fillRect(55, 58, 2, 6, WHITE);
    case 8: display.fillRect(50, 58, 2, 6, WHITE);
    case 7: display.fillRect(45, 58, 2, 6, WHITE);
    case 6: display.fillRect(40, 58, 2, 6, WHITE);
    case 5: display.fillRect(35, 58, 2, 6, WHITE);
    case 4: display.fillRect(30, 58, 2, 6, WHITE);
    case 3: display.fillRect(25, 58, 2, 6, WHITE);
    case 2: display.fillRect(20, 58, 2, 6, WHITE);
    case 1: display.fillRect(15, 58, 2, 6, WHITE);
  }
}

void statup_text() {
  display.setTextSize(1); display.setCursor(13, 18);
  display.print("Si5351 VFO/RF GEN");
  display.setCursor(6, 40);
  display.print("JCR RADIO - Ver 2.0");
  display.display(); delay(2000);
}

10kHz to 225MHz VFO/RF Generator with Si5351 - Version 2