The VFD Modular Clock is a clock based on old-fashioned VFD Display Tubes.

VFD is short for Vacuum Flourescent Display. A VFD display is typically green or blue, and emits a bright light with high contrast. VFD Displays are often found in car radios.

A VFD Display tube looks like an old Vacuum Tube, the predecessor to the transistor. The inside of the tube contains segments that can be lit up to form numbers and letters. Most tubes contain segments for one digit, and several must be stacked together to make a complete display.

The clock itself is modular, it comes with a base board, which is powered by an ATMega32U4 microcontroller and contains a high-voltage VFD driver that is used to light up the display shield that sits on the top board.


Currently, five different shields are available (with more to come later on).

Each shield is coded with a 3-bit numerical indentifier. This allows the firmware to automatically recognize the shield that is plugged in and it will adjust the display automatically. Support for shields added in the future will be released as firmware upgrades.

  • IV-6 Display Shield: Contains 6 medium 7-segment Russian VFD tubes. The display is blue/green.
  • IV-17/IV-4 Display Shield: Contains 4 large alphanumeric 16-segment Russian VFD tubes. The display is blue/green.
  • IV-17/IV-4 Display 6-digit Shield: Contains 6 large alphanumeric 16-segment Russian VFD tubes. The display is blue/green.
  • IV-22 Display Shield: Contains 6 top-view 7-segment Russian VFD tubes. The display is blue/green.
  • IV-18 Display Shield: An 8-digit 7-segment single-tube elongated Russian VFD tube. The display is blue/green.

Acrylic Enclosures

Acrylic enclosures that match each of the shields available separately.

Four Letter Word add-on board

A small board that adds four letter word functionality to the clock is available. This board is meant for version 1 of the base board only. Version two (marked as mk2 on the board) has this functionality built-in.

See here for details


  • Modular design: The display tube shields are swappable
  • HV5812 VFD driver with 20 outputs: Can drive up to four 16-segment alphanumeric displays or twelve 7-segment numerical displays.
  • Open source firmware (available at GitHub)
  • Arduino Leonardo bootloader. Can be programmed using just a USB mini-b cable
  • DS3231M Real Time Clock with backup battery


The firmware has shield detection built in, so it knows which Tube shield is plugged in, and adjusts the output accordingly. With the IV-17/IV-4 alphanumeric display shield, you get four alphanumeric characters. With the IV-6 7-segment display shield, you get six alphanumeric characters (since this is a 7-segment display, some characters are displayed in a stylized manner. ‘x’ and ‘z’ cannot be displayed at all).


If you run into trouble during assembly, have a look at the troubleshooting page

If you have version 2 (mk2) of the board, and your clock is running slow, please refer to the repair guide