Vacuum Fluorescent Displays


VFD's are typically seen on VCR's and CD players. Unlike LCD's they are very bright and are clearly visible even from a distance in a well lit room. They are vacuum devices made of glass so they are quite fragile.

Short Explanation of VFD'S:

A VFD is a triode valve with a phosphor coated anode (+). Phosphor glows when hit by electrons. The filaments (cathode, -) of the VFD emits electrons. The filaments are the thin wires that run horizontally across the display. In between these two is the grid. Apply voltage to the grid and the electrons travel for cathode to anode, they hit the phosphor and that results in light. The color is determined by the type of phosphor. Below is a VFD with orange and green phosphor coatings.

This VFD is from an old VCR.

In practice each symbol, or "segment" on the VFD is lit by first applying voltage to the filaments then a greater voltage to one of the grids and a segment.




Powering up a VFD with a PC PSU:

My AT PSU powering the VFD. I have glued a strip of  screw-connectors to the top to get easy access to the various voltages. Not everyone can afford expensive lab type power supplys. ^_^

This display has 21 leads. 2 are used for the filament. I wanted to test out a bunch of stuff with it and connect it in various ways so I soldered wires to each of them. The leads farthest to each side are the filament leads. I put an 27ohm resistor in series with the filament and connected it to the +5V (Yellow) and GND (Black) of the PSU. Connecting it without the resistor caused the filaments to glow red hot!







To take the photographs where the entire display is lit i connected all the remaining leads (not those for the filament) to the +12V (Red) of the PC power supply. This is not the best way to light a display, to get even brightness an AC driven filament is the best. As you can see the REC indicator is very dim compared to the rest of the display (it IS lit). Overall brightness can be increased with a power supply that can produce more suitable voltages for VFD's.


Links:
Putting a Vacuum Fluorescent Display in a Microwave - Everyone likes destroying stuff, especially if it involves fire and sparks! ^_^ Pictures and a video.
VFD Ring Modulator - Using a display to produce nice audio effects.
Vacuum Fluorescent Display (VFD) - A good explanation of how VFD's work.

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Last Updated: 2006-02-09