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
• Fits within HW-9 VFO Box
• Controls frequency 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
  • Band pass filters to turn square waves to sine waves
  • 27 MHz crystal