Sunday, 18 March 2012

Vacuum Fluorescent Display

In his world wide travels, LegionLabs picked up a little vacuum fluorescent display showing micro, amps and volts.  Definitely a unique souvenir!  I'd never worked with VFDs before, but in the end, they are quite simple.  A hot filament emits electrons, which are evened out by a grid and then impact on fluorescent surfaces.  They run at relatively low voltages, as compared to, say, Nixie tubes.

The leads are pretty easy to figure out just by examination.  I followed the directions here and pretty quickly had it working.

Heres a zoom out on the setup.  On the right is a slapped together bench supply, using an LM315.  Its running the filament at 1.24 V, with no limiting resistor.  This is pulling 35mA, on start up it pulls quite a bit more (~50), but it quickly reaches temperature and stabilizes there.   In real use, I may try to reduce that current a little.

I have no idea why there are so many leads on the tube.  Theres only the three elements inside (micro, V and A),  each element is connected to several leads, but they dont seem to be lighting up different parts - they are just redundant.  Go figure.


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