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From: John Fields on 2 Dec 2006 11:03
On Sat, 02 Dec 2006 10:38:00 -0500, Spehro Pefhany
<speffSNIP(a)interlogDOTyou.knowwhat> wrote:

>On Sat, 02 Dec 2006 08:42:44 -0600, the renowned John Fields
><jfields(a)austininstruments.com> wrote:

>>Sorry, Charlie, but vacuum fluorescent displays _do_ have filaments.
>>
>>Where do you think the electrons used to illuminate the phosphors
>>come from, otherwise?
>
>The Beckman displays were flat panel plasma discharge displays, sort
>of like Nixies but segmented and with the segments all in one plane.
>You used to seem them on gas pumps until fairly recently as well as
>some industrial instruments (Simpson had a fairly successful series of
>instruments that used them). National semi made a biplar driver chip
>DS8880 or something like that.. ah, here it is:
>http://www.sphere.bc.ca/test/nixies/ds7880.pdf

---
I stand corrected; thanks :-)


--
JF
From: Spehro Pefhany on 2 Dec 2006 11:37
On Sat, 02 Dec 2006 10:03:54 -0600, the renowned John Fields
<jfields(a)austininstruments.com> wrote:

>On Sat, 02 Dec 2006 10:38:00 -0500, Spehro Pefhany
><speffSNIP(a)interlogDOTyou.knowwhat> wrote:
>
>>On Sat, 02 Dec 2006 08:42:44 -0600, the renowned John Fields
>><jfields(a)austininstruments.com> wrote:
>
>>>Sorry, Charlie, but vacuum fluorescent displays _do_ have filaments.
>>>
>>>Where do you think the electrons used to illuminate the phosphors
>>>come from, otherwise?
>>
>>The Beckman displays were flat panel plasma discharge displays, sort
>>of like Nixies but segmented and with the segments all in one plane.
>>You used to seem them on gas pumps until fairly recently as well as
>>some industrial instruments (Simpson had a fairly successful series of
>>instruments that used them). National semi made a biplar driver chip
>>DS8880 or something like that.. ah, here it is:
>>http://www.sphere.bc.ca/test/nixies/ds7880.pdf
>
>---
>I stand corrected; thanks :-)

Not really a correction, for you anyway, as "Fluorescent" wasn't an
accurate description. The neon plasma discharge emits light directly.

Anway, a trip down memory lane.

http://www.decodesystems.com/sp-351-1.gif
http://www.decodesystems.com/sp-351-2.gif


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff(a)interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
From: jimi on 2 Dec 2006 14:10

John Fields wrote:
> On 1 Dec 2006 12:29:20 -0800, "jimi" <jim_fen05(a)yahoo.co.uk> wrote:
>
> >Thanks for the replies, however, I asked the question so I could avoid
> >using a microcontroller.
>
> ---
> Is this application for a one-off, or are you planning on building a
> quantity of these?
>
>
> --
> JF

It's a one off.

From: bill.sloman on 3 Dec 2006 18:30

John Fields wrote:
> On 2 Dec 2006 05:03:07 -0800, bill.sloman(a)ieee.org wrote:
>
> >
> >John Fields wrote:
> >> On 1 Dec 2006 22:06:01 -0800, bill.sloman(a)ieee.org wrote:
> >>
> >> >
> >> >John Fields wrote:
> >> >> On 30 Nov 2006 13:24:39 -0800, "jimi" <jim_fen05(a)yahoo.co.uk> wrote:
> >
> ><snip>
> >
> >> Yes just the filament supply for all those 12AT7's must have been
> >> unwieldy, to say the least.
> >> ---
> >
> >I don't know what you were doing in 1972 - the fact that you haven't
> >yet got past 555's does suggest that you aren't an early adopter
>
> ---
> I'd say that statement more nearly categorizes your position than
> mine since I adopted them way back when they first came out. You,
> on the other hand, have yet to use one (by your own admission) so
> I'd say you're the one who's a little late getting on the bandwagon.
> ---
>
>
> >- but
> >my toy used TTL logic and Beckman 7-segment fluorescent displays, with
> >a few transistors to handle the voltage swings.
> >
> >And not a filament in sight (nor any hidden filaments either)
>
> ---
> Sorry, Charlie, but vacuum fluorescent displays _do_ have filaments.
>
> Where do you think the electrons used to illuminate the phosphors
> come from, otherwise?
> ---

>From positive ion bombardment of the negatve electrode - the "glow
discharge" discharge mechanism - in a low pressure of some noble gas
(probably neon, but I can't be sure) and certainly not fom a filament.
There was a small, steady "keep alive" corona discharge hdden behind an
opaque bit of the glass front, and the active segments lit up when you
hit them with something over 180V, whch would have been around the
Passchen minimum for avalanche discharge through neon. Without the
keep-alive discharge, fast multiplexing could be chancey - it was an
added extra feature in the second generation of the displays.

> >Looked quite neat.
>
> ---
> Yeah, I'm sure. VFD's are most always pleasant to look at.

Agreed. The Beckman displays were nicer than most but the 180V seems to
have been unpopular.

--
Bill Sloman, Nijmegen (but in Sydney at the moment).

From: jasen on 8 Dec 2006 16:47
On 2006-12-02, bill.sloman(a)ieee.org <bill.sloman(a)ieee.org> wrote:
>

> I'd prefer a programmable logic part - the 4-digit counter is not
> synchronous with the multiplexing logic for the display.
> Back in 1972 I dealt with this problem by freezing the multipexing
> clock until any
> incoming count had rippled through the (asynchronous) counters, which
> took up to 4usec. This wasn't an elegant solution. With a
> microcontroller, I guess you'd rely on the interrupt system to capture
> clock increments that occured at the wrong instant, and you'd keep your
> interrupt handler short and quick to keep the maximum count rate
> respectable.

easier to just use the built-in hardware counter,

AtTiny2313 has a 16 bit hardware counter, set the limit register to 10000
and you can have a hardware carry output.
loop that output back to the input for the other 16 bit counter and you could
drive 8 digits, but for the lack of enough I/O pins

the display, (which usually need only be fast enough for human perception)
can then be done in software.

> Programmable logic offers true parallel processing, which can be a lot
> tidier.

so do microcontrollers (to a limited extent)

Bye.
Jasen
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