November 4, 2013 AT 9:20 am

#Macro Monday: Ice Tube Clock

vfd1_600

The Ice Tube Clock, available as a kit, uses a lovely IV-18 vacuum-fluorescent display (VFD) tube.

vfd2_600
Unlike Nixie tubes, which are current-operated gas-discharge displays, VFDs are thermionic voltage-controlled devices, just like the vacuum tubes used in old radios and amplifiers (as well as some modern high-voltage equipment). Specifically, VFDs are a special kind of directly-headed triode.

VFDs have three basic parts: the filament (cathode), the grid, and the phosphorescent anode(s). In the case of the IV-18 device used in the Ice Tube, the entire tube has two filament wires stretching the length of the tube (wired in parallel). Each separate digit has it’s own grid, and each of the 7 segments of the number display are ganged together is an anode. By quickly multiplexing the grids you can make the device appear to display all the digits at once.

In this photo you can see all three electrodes. Those two dark lines running horizontally across the photo are the filament wires.

vfd3_600

Here you can see a couple of illuminated digits. The nebulous nature of the illumination across each segment is caused by variations in the electric field, and the grids casting an electron shadow onto the segments.

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6 Comments

  1. I was wondering if it is possible to buy just the tube (and the breakout board), as my ice tube clock fell two weeks ago and the tube shattered inside the acrylic box. I could order the IV-18 VFD retro display from ebay, but I’d rather continue supporting you guys.

  2. @steve: yup! http://www.adafruit.com/products/242

    also, the tube PCB: http://www.adafruit.com/products/343

  3. Thanks johngineer! I searched the site but couldn’t find them, awesome, now I’ll be able to tell time again!

  4. bill earl - adafruit_support

    Nice work John! Putting those T&S bellows to good use I see. Is the second photo taken through the glass, or did you remove the grid from a broken tube?

  5. Thanks, Bill!

    For the second photo, I grabbed one of the tubes that didn’t pass QC and cracked open the glass envelope.

  6. very nice. might get this kit. working on a numitron tube clock at the moment, similar era, different technology. love old fashioned displays. :D

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