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?

• Toroid Calculator
• A short guide to harmonic filter for QRP transmitter output
  • PE-0805CLH1R5STS Example 1 uH inductor
  • Search PE inductors
  • Broader search
  • 0805 caps C0G

• VFO and BFO frequencies are outside the bands (deliberately to void collisions)

BFO Filter

• 8.8314 MHz in receive
• 8.8307 MHz in transmit

Libraries/Example Code

• Land Boards Application
• VFO and BFO with Si5351A, OLED and Arduino
• U8g2: Library for monochrome displays, version 2
• Si5351 Library for Arduino
• Universal Digital VFO Si570/Si5351
• Adafruit_Si5351
• Si5351 Library for avr-gcc
• vk3hn_VFO_controller
• Simple BFO with si5351 controlled by Arduino

Videos

VFO Design

• Charlie Morris YouTube channel

Mods

• 4 Led's in the HW-9 taking only 5 MA when wired in series with a 2200 ohm 1/4 watt resistor.
• A total of 20 MA to light the dial and meter.
• The space between the front panel and the chassis here is very small so the tiny LED's are required to do the job .