HW-9 VFO

This is a work in process - Gathering pieces.

Features

Replace HW-9 internal VFO with a digital VFO

HW-9 VFO has legendary issues
- Mechanical issues with vernier
- Drift due to thermal
- Lack of resolution
- Backwards dial
Fits within HW-9 VFO Box
Controls Tx/Rx/BFO frequencies with rotary encoder
- 10 Hz steps
DD1306 OLED Display
- I2C Interface
- "Curved" display
Uses RIT control on HW-9
- +/- 1 KHz RIT
Blue Pill Microprocessor
- Arduino compatible
- 3.3V
Understands band switch for MHz displayed
Si5351 Oscillator
- I2C Interface
- 3 Outputs
  - Transmit frequency
  - Receiver frequency include offset plus RIT
  - BFO frequency
- Low pass filters to turn square waves to sine waves
- 27 MHz crystal

Schematic

Connections to Radio

RIT pot
- Connects to Analog input
  - Polled occasionally while in receive
Band switch
- SW1 9V
T/R - transmit/receive

Parts

Blue Pill Card

Blue Pill Card

3.3V operation work without level shifters for I2C
- OLED can run from 3.3V
- Si5351 can only run from 3.3V
Used right angle headers and Dupont cables
Replaced BOOT 0,1 jumpers
- Jumper on BOOT1
- Switch on BOOT0 - easier to download code
Download via serial
Arduino IDE

128x32 OLED

Ebay

Arduino Library for OLED

U8g2: Library for monochrome displays, version 2
- Reference library
- Constructor

U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);   // STM32, Ebay OLED

List of Fonts

  u8g2.setFont(u8g2_font_ncenB14_tr);

Hello World Code

U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);   // STM32, Ebay OLED

void setup(void) {
  u8g2.begin();
}

void loop(void) {
  u8g2.clearBuffer();			// clear the internal memory
  u8g2.setFont(u8g2_font_ncenB08_tr);	// choose a suitable font
  u8g2.drawStr(0,10,"Hello World!");	// write something to the internal memory
  u8g2.sendBuffer();			// transfer internal memory to the display
  delay(1000);  
}

Rotary Encoder/Breakout Board

Includes pushbutton Switch
Includes Pull-Up resistors
Needs R/C filter on output for debounce
Reading Rotary Encoders - Arduino reference
Simple Rotary Encoder Arduino library
Library for the Arduino environment for using a rotary encoder as an input

Si5351 Frequency Generator

I2C Daisy-chain connector
3 outputs
- Tx
- Rx (may not need to use separate output)
- BFO - could be adjusted

VFO TX

250 KHz range
- From 5.9993-5.7493 MHz

VFO RX

RIT knob is taken in through an A/D and adjusts the receive frequency plus/minus 1 KHz

BFO

8.8314 MHz in receive
8.8307 MHz in transmit
700 Hz difference but could be adjusted

Low Pass Filters

Si5351 has square wave outputs
LP filter can be used to change squarewave into sinewave
LC Filters Design Tool - calculator
Kits and Parts dot Com
- Build a 7-pole Universal Low Pass Filter for HF
- Butterworth
- Replace with SMT card?