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[DPRG] Vacuum Fluorescent Displays

Subject: [DPRG] Vacuum Fluorescent Displays
From: Randy Carter rwcarter at foxinternet.net
Date: Wed Oct 25 09:39:47 CDT 2000

The micro controllers were specially ordered with the high
voltage outputs to drive the displays.  The arrangement is that
all of the A segments are connected together, and the B's etc. 
Then each digit is pulsed so that only the desired charter is lit
up.  This is the same arrangement you would fund in multiplexed
LED displays.  

You have to constantly scan these displays to keep them glowing. 
If your display has 5 sections and you have to refresh each
section at least 25 times a second then you have to place new
data on the drive pins at a rate of 125 times per second.  With
more sections (I have seen as many as 10) you have place your
data even faster.

To run these displays you need a -30v and +5v power supply.  The
filament usually runs at 3 volts biased at -25v (zener off of
-30v).  A lit segment has its segment pin and section pin pulled
up to +5v.  A unlit segment has its section puled to -30 and the
segment is at any other voltage.

Patrick Innes wrote:
> I have recently run across several old (and quite
> dead) VCRs, and am in the process of converting them
> into spare parts for the workbench.
> Among the components are several vacuum fluorescent
> displays, without onboard drivers of any kind.  I am
> curious as to just what sort of drive circuitry is
> involved in getting these things to light up.  I
> realize that I'm looking at some form of alternating
> current or pulsed DC, but as to required frequencies
> and voltages, I'm entirely in the dark, as the VCRs in
> question were quite a ways beyond the point of
> providing this information by the time I got my hands
> on them.
> Any help you could provide along these lines would be
> greatly appreciated, as I've already come up with
> several ideas to apply these things towards, not the
> least of which is a robot that continually flashes
> 12:00 while it's running.  :^)
> -- Patrick
>    KC5UGQ
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