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