Sylvia VFD Tube Clock

Designed by Dieter Wächter
last update and finished: September-07-2008

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This clock-project bases on the VFD-tubes technology.

What are VFD-Tubes?
A vacuum fluorescent display (VFD) tube is a type of tube which consists of a hot cathode (filaments), anodes (phosphor) under a high vacuum condition in a glass envelope.
This clock uses tube types 8843 or 8894 made by Sylvania in the early seventies. The cathode is made up of fine tungsten wires, coated by alkaline earth metal oxides, which emit electrons when heated by an electric current. If electrons impinge on the phosphor-coated plates, they fluoresce, emitting light to indicate the 7-segments used in this tubes. Electrons can only reach (and "illuminate") a given plate element if the plate is at a positive potential with respect to the cathode. They have no grid compared to other VFD displays.

Here, at my VFD-tube page you can find lots of pictures and descriptions of VFD tubes.

Here an example of the 8843 tubes:


Step 1: Designing the schematic

After studying the datasheets and some tests on the display I made some test circuits and finally came to this schematic:

As you can see a very simple design.
HV5812WG drivers, a step-down converter for the 1.5V power supply (filaments) and a step-up converter for the 27V anode supply.
Atmega, and finally the Dallas RTC (DS1337C ) which has an on-board crystal (I like that all-in-one chips)
I think there is nothing to explain in this schematic.

Step 2: Designing the board

Here the production steps:









The board measures: 180x67mm

Step 3: Assembling the board

There were no difficulties with the schematic.
Everything worked fine, although it was the first prototype.



Step 4: Assembling the board with the tubes.



Step 5: Designing the case

I made some designs and came to this one (3D-animation only)
It is the same as I used for my X2000 clock.

Here you see the result of the finished housing:

Step 6: The coding

The features I put in:

  • 12/24h mode
  • Date in configuration DD.MM.YY or MM.DD.YY
  • Leading zero suppression: The leading zero can be blanked or shown
  • Cross fading: different modes to fade the digits from one number to the next
  • Alarm clock
  • Power Down Mode: tubes and supply can be totally switched off for a user programmed period in order to save energy and increase life expectancy of the tubes
  • Time is battery buffered when no line power is available; battery will last for more than 10 years
  • RTC drift compensation: Every RTC chip (RTC=Real Time Clock) does have a drift. This drift depends to the ambient temperature, buffer battery voltage, aging and other factors. This clock has a feature called “drift compensation” which allows compensating that drift nearly to zero.
  • User settings are always stored

This Project is finished
Thanks for reading.

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