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TM6VFO_V6.2S

 New TM6VFO Update! VFO + BFO + XO Crystal Calibration 

Homebrewers and radio enthusiasts…

I’m excited to share a major update to the TM6VFO project based on Arduino Nano + Si5351 + TM1637 display!

This sketch turns a simple Nano into a professional‑grade VFO/BFO controller, with features normally found only in commercial transceivers. What’s new in this version?

 Full Si5351 VFO (CLK0)

Controlled by a rotary encoder

Selectable tuning steps: 10 Hz / 100 Hz / 1 kHz

Clean 6‑digit TM1637 display

Automatic EEPROM storage

 BFO for LSB (CLK1)

Fixed IF at 12 MHz

BFO base at 11.997500 MHz (FI – 2.5 kHz)

Fine adjustment range: ±2000 Hz

Real‑time tuning with the encoder

Stored in EEPROM

Perfect for 2.4–2.7 kHz SSB filters.

 NEW: Si5351 Crystal Calibration by Frequency Coincidence (XO Calibration)

The Si5351 uses a 25 MHz crystal that is never perfectly accurate.

Typical error: ±10–50 ppm, which causes:

VFO drift

BFO offset

IF misalignment

Displayed frequency not matching real frequency

The TM6VFO now includes a full XO calibration mode, allowing you to correct the crystal error by ear, with no test equipment.

How it works:

Tune to a known reference signal (AM station, beacon, WWV, another rig).

Enter XO calibration mode.

Turn the encoder until the signal matches the displayed frequency exactly.

The correction value is saved to EEPROM.

Result:

 VFO accurate to the Hz

 Perfectly centered BFO

 Your rig aligns with commercial radios

 Additional features

 Adjustable display brightness

7 levels

Long press to activate

Blinking indicator while adjusting

 Welcome messages

“U6.2”

“73”

 Stable encoder handling

Debounced

Direction detection

Smooth tuning

 Intuitive one‑button menu

Short press → change tuning step

Long press → brightness mode

Very long press → BFO calibration

Special long press → XO calibration

 What can you use this VFO for?

Perfect for:

Homebrew receivers and transceivers

QRP projects

FI–VFO conversion rigs

LSB/USB SSB radios

Replacing analog VFOs

Experimenting with the Si5351

 Final thoughts

The TM6VFO is no longer just a VFO…

It’s a complete frequency control system, featuring:

Precise VFO

Adjustable BFO

XO crystal correction

EEPROM memory

TM1637 display

Professional‑style menu

Ready to drop into your next homebrew transceiver!