If you ever destroyed an old CD- or DVD-player or a VTR for parts, you may have taken a good look at its display. Sometimes, it's just an ordinary LCD, but in other cases it's a magnificent piece of glasswork called a VFD. While as old as the vacuum tube, the VFD is still used because it's self-illuminating and is able to spit out quite some light.
A VFD basically is a vacuum tube: it has a filament which a current runs through so it heats up and spits out electrons. These electrons will be attracted by the displays segments, but only if the grid in front of it doesn't stop them first. If you're unsure about the workings of a VFD, there are a few places on the Internet which explain how they work.
The problem with VFDs salvaged from old electronics is that they usually have a completely unusable controller, so if you want to make use of the VFD, you'll have to design a controller yourself. A VFD isn't a simple TTL logic device though: it requires voltages of 12 up to, for some old VFDs, 50V to drive the segments and gratings/grids. Because of the fact that standard logic and microcontrollers usually end up completely fried when fed with a voltage above 5V, voltage conversion is needed for the VFD. An example of how that can be archieved is documented on this page, which uses two transistors and 4 resistors to convert a logic voltage between 0 and 5V to a higher voltage.
While this is a fine solution, it would mean that if I ever ran into a nice VFD I wanted to drive, I would have to solder two transistors and four resistors per VFD-input, which could become a bit of a hassle...
1 Next »