This is a flexible multi-band VFO firmware running on the Arduino platform, driving a Skyworks (formerly SiliconLabs) Si5351 DDS.

This work started from the Multifeatured VFO project by Jason Milldrum (NT7S) and Przemek Sadowski (SQ9NJE), and moved to the goal of implementing a set of features generally available in commercial-grade transceivers, while keeping focus on performance and maintainability.

It relies on

• Jason Milldrum (NT7S)'s Etherkit_Si5351 library, to drive the Si5351 DDS module,
• Ben Buxton's Rotary library, to control a rotary encoder,
• Frank de Brabander's LiquidCrystal_I2C library, to drive a I2C LCD display.

This project is licensed under the terms of the GNU General Public License v3.0.

Initial authors: Giovanni Caracuta (I7IWN) and Francesco Cisotta (IZ2QPV).

[!NOTE]
A fork of this project is available, addressing single band RTX operations. While one band only is supported in this variant, this allowed featuring complete band configuration at runtime (band limits, along with conversion design, power levels, etc. may be set in the calibration menu, with the front-end controls). Thus, no coding is required to set up firmware for the RTX project.

Table of contents

• Hardware requirements
• Circuit connections
• User Interface controls
• Build control
• Operation information
• Operation workflow
  • Calibration menu
  • VFO Dial
  • Memory Dial
  • Operating menu
• Contributions and future updates

Hardware requirements

Other components are outlined in the circuit schematic below.

Circuit connections

PCF8574 configuration

User Interface controls

Blue-labeled button functions may be activated by a long press (> 1 s).

Red-labeled button functions are enforced at boot time.

Build control

Library dependencies

The adopted version of each library is bundled with the firmware, for ease of build.

[!NOTE] ¹ The following patch is applied on the embedded Etherkit library code, in order to succesfully set a new PLL freq after crossing the SI5351_MULTISYNTH_MAX_FREQ threshold downwards: in the uint8_t Si5351::set_freq(uint64_t freq, enum si5351_clock clk) method, at line 314, the call to pll_reset() is uncommented.

Operation information

The firmware may drive frequency synthesis according to the transceiver design, among the following:

• Direct conversion
• Single conversion
• Freq x 4

You configure the hardware design, along with other design parameters, in the Calibration menu.

Whichever the design is, the following band limits are pre-configured, matching IARU/ITU bandplan for Region 1.

[!CAUTION] You are required to amend frequency constraints according to current regulations at the time of operation, or when a different Region applies. (For this purpose, update band limits in smart-vfo.ino at line 282, and adjust default entry frequencies accordingly in memory.ino at line 266. Finally increase EEPROM_DATAMODEL_VERSION in smart-vfo.ino at line 298, for changes to apply.)

Two independent VFO tuners (V_A and V_B) and 40 memory channels are available, persisting each:

VFO tuners persist individual operating data for each band.

Operation workflow

During an operating session, the user moves around the following operating states, which are described in the sections below.

stateDiagram-v2
    [*] --> CMNU
    CMNU: Calibration menu
    MENU: Operating menu
    VFO_DIAL: VFO dial
    MEM_DIAL: Memory dial
    [*] --> VFO_DIAL
    VFO_DIAL --> MEM_DIAL
    MEM_DIAL --> VFO_DIAL
    VFO_DIAL --> MENU
    MEM_DIAL --> MENU
    MENU --> MEM_DIAL
    MENU --> VFO_DIAL

At boot time, the firmware enters the VFO dial state, where tuning is allowed on either of the two VFOs.

• Keep the BAND UP button pressed at boot time to step into the Calibration menu.

• If the BAND DN button is pressed at boot time, the factory default configuration is restored into EEPROM (all user data and settings are lost!).

Calibration menu

The display shows the available configuration items on the first line, and editable values on the second one.

The following settings may be customized under this menu. They are persisted into the EEPROM, and may always be reset to factory defaults as described in the section above.

DDS calibration is allowed at runtime, since the Si5351 is powered and CLK0 set to a reference frequency of 10,000 MHz while editing the correction factor. Please tune this parameter until the output measured on CLK0 is as close to 10 MHz as possible. Then press ENTER.

Features

• Menu is navigated through the ENTER, ESC buttons and DIAL control to rotate values.
• The STEP button allows modifying the step of increments of the DIAL control over numeric values.

VFO Dial

The display shows current VFO and tuned frequency, active modulation mode and possible RIT.

During operation, other flags are displayed to report for active features.

Features

• With DIAL control you may rotate frequency (step may be adjusted with STEP button).

• By pressing ENTER, direct frequency entry mode is initiated. Type frequency with the digit buttons or press ESC to quit. Frequency is accepted and tuned as soon as the last digit is entered. Current VFO automatically switches to the band matching the frequency entered.

• When RIT button is pressed, DIAL control focus is moved to the RIT value. An independent RIT rotation step may be now adjusted with the STEP button.

• The MODE button allows rotation among the supported modulation modes.

• The SPLIT button activates the SPLIT mode, which switches to the frequency and mode of the opposite VFO during TX operation.

• The A/B button allows switching between the two available VFO tuners.

• The A=B function overwrites the opposite VFO record for current band with operating values of current VFO.

• The M.IN (memory input) function allows storing current VFO record into a memory channel. When activating this function, the target memory channel must be selected with the DIAL control. Non-empty channels are marked with a full circle symbol (●).

• The LOCK function inhibits any control on the UI, allowing only RX|TX switching.

• The MR (memory recall) button switches into the Memory Dial state.

• The MENU function opens the Operating menu.

Memory Dial

The display shows current memory channel, along with its frequency, mode and possible RIT currently tuned.

During operation, other flags are displayed to report for active features.

Features

• With DIAL control you may rotate among populated memory channels.

• By pressing ENTER, direct channel entry mode is initiated. Type channel with the digit buttons or press ESC to quit. Channel is accepted and tuned as soon as the last digit is entered. Modulation mode and RIT value cannot be adjusted while in the memory browsing state. To apply an adjustment, shift the memory channel record to a VFO tuner, as described in the point below.

• The M🞂V function allows shifting current memory channel to current VFO, overwriting the matching band record. With this action, VFO dial state is stepped back into.

• The LOCK function inhibits any control on the UI, allowing only RX|TX switching.

• The VFO button switches into the VFO Dial state.

• The MENU function opens the Operating menu.

Operating menu

The display shows the available configuration items on the first line, and editable values on the second one.

The following settings may be customized under this menu. They are persisted into the EEPROM, and may always be reset to factory defaults as described in the section above.

The second to last menu item allows monitoring the Si5351 device status, through the following runtime params (refer to Etherkit release notes for their meaning):

The last menu item shows current firmware version and date of release.

Features

• Menu is navigated through the ENTER, ESC buttons and DIAL control to rotate values.
• The STEP button allows modifying the step of increments of the DIAL control over numeric values.

Contributions and future updates

Please feel free to report issues and submit pull requests with improvements and new features, and stay tuned for fixes and updates!

Giovanni Caracuta (I7IWN) and Francesco Cisotta (IZ2QPV)