Driving a VFD

VFD FIP8A5RLately I found a VFD tube in my junk box and thought of driving it. Soon realized that it is not as easy as driving an LED display. I have a couple of FIP8A5R VFD tubes manufactured by NEC. The advantage of VFDs over LED display or an LCD display is their unique blueish-green brightness. Each segment of a VFD glows bluish-green and looks great. It does not suffer from the viewing angle problems like LCDs do. The newer superbright LED displays are trying hard to reach to the coolness level of VFDs.

To drive a VFD one would need three inputs:
  • Filament voltage
  • Grid drive
  • Segment drive


I knew that the VFDs operate on the same principle as the vacuum tubes. The filament would warm up and "boil" electrons off of it (cathode). The electrons would be attracted by the anode (segments in this case). To reduce the number of pins on the display, grids are deployed. Grids would allow or disallow the electrons to flow thus controlling digts in multiplexed architecture.

I connected a 3V battery on the filament and it started to glow. Later I connected the G1 (grid of display1) and a segment to positive terminal of the battery. A segment on the display 1 should have lit but it didn't. :-(

I asked for help on Piclist and John DeGood responded with some information on driving them. John reminded that the VFDs operate like a triode tube so I used a different approach like this...

How tubes work

Later, I was able to light up a couple of segments using two batteries. I connected a 3v battery to the filament and connected another 9v battery with positive terminal on the grid and the segment and the negative terminal on the filament where negative terminal of 3v battery was connected.

I didn't connect the filament's positive terminal to the battery
directly, instead I connected the wire momentarily to the filament. I
noticed that when I completed the circuit to the filament, it would
glow dim but once I interrupt the circuit the segment would glow
bright to dim and turn off (like a capacitor). So I need to oscillate
the filament as John suggested.

Prashant from Silicon Junction also shared his experience as he did a similar project that is on his website.

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