Chetan Bhargava wrote:

>I'm trying to start-up on VFDs.
>
>As far as I understand, VFDs have three inputs:
>
>1. Filament
>2. Grid (or Common Anode in LED terms)
>3. Segments (Anodes in LED terms)
>
>To light up a VFD segment on a digit I have to:
>1. Apply filament voltage
>2. Apply +v on the display grid
>3. Apply +v on the segment
>
>Is it enough to light up a segment or am I missing anything?
>
>Any pointers would be appreciated.
>
>Thanks,
>
>--
>Chetan Bhargava
>Web: http://www.bhargavaz.net
>Blog: http://microz.blogspot.com
>  
>

A VFD is basically a triode vacuum tube, so you'll also need to bias the 
cathode.  The VFD filament usually doubles as the cathode ("directly 
heated cathode" in vacuum tube parlance).  The cathode voltage is 
typically applied via a filament transformer center-tap.

In a product I designed many years ago I connected one end of the VFD 
filament directly to the cathode bias voltage and drove the filament 
with a square wave applied to the other end through a DC blocking 
capacitor, thus eliminating the filament transformer.  If you try that 
trick be sure you don't exceed the VFD inter-element voltage maximums, 
as the driven end of the filament will almost certainly have larger 
voltage excursions relative to the other tube elements than encountered 
with a center-tapped transformer drive.

John
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist