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'[EE]:Fluorescent displays'
2000\08\19@085136 by Jinx

face picon face
I'm having some trouble getting a Futaba VFD going. There are
two data sheets that conflict, and rather than blow the tripes out
of it by mistake I'd appreciate a pointer or two. I've tried Futaba
service a couple of times but apparently no one's awake this
month and there's b-all on the web. Plenty about LED/LCDs, no
VFDs

It's a pretty basic 11-ST-26ZA. This is an 11 digit numeric display
with upper and lower commas and decimal point. The SIL pin out is

1,26  Filament
2,3,25  NC
4,6,8,10,12,14,16,18,20,21,32      11G,10G,9G,...1G
5,7,9,11,17,19,22  g,f,e,d,c,b,a
13  comma2
15  DP
24  comma2

The data sheet from Futaba says (typical values)

Filament Voltage 4VAC @ 18mA
Anode,Grid Voltage 20Vp-p
Anode,Grid Supply Voltage 24.5Vp-p (starting to lose me)
Duty Factor 1/15
Cathode Bias 4.5VDC (applied to the C-T of the Filament Tx winding)
Grid Cut-off Voltage -5.0V (lost me)
Anode Cut-off Voltage - no value (why mention it then ?)

Apart from physical diagrams, that's it

The data sheet for the Allegro 6118 driver shows one end of a line
to be VBias and the other end VFil. This is where things are getting
fuzzy. Is Cathode Bias the same as VBias ? Why show it as part of
the Filament ? If Cathode Bias connects to Tx C-T and the other end
of this line is VFil, why have a C-T transformer ?

Getting data to the display would seem to be easy enough. Making
it visible is another matter. Does anyone have a practical circuit or
can explain the terms used in the data sheets ? For example, exactly
what is required by way of power supplies ? If Futaba's aim was to
baffle me, mission accomplished

TIA

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A subtle thought that is in error may yet give rise to fruitful
inquiry that can establish truths of great value.

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2000\08\19@153353 by Oliver Broad

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face
Triode biasing.

The only reason I know for AC on the filament is to achieve even
illumination of the display, otherwise it may be possible to see the
negative end as brighter. For early tests it's often possible to feed the
filament from 5v and connect a resistor or diodes between the other end and
ground. If you do use a transformer that center tap bias can be a zener
diode.

Hopefully if you float the filament enough above ground then ground will be
sufficiently low for both grid and anode cutoff. If the drivers you use pull
down as well as up then you shouldn't have to worry. If they don't then you
will need pull down resistors on the grids and they may not cut out fully.

24.5v is the recommended anode supply relative to ground. Subtract their
recommended cathode bias of 4.5v and you get 20v. Not sure why they say Vp-p
but if the power was a low voltage, say 5v, then a transformer might be used
to supply filament AC and another winding would provide 24v, which might not
need to be properly smoothed.

Oliver.

{Original Message removed}

2000\08\20@153959 by Peter L. Peres

picon face
>fluorescent

How to steer: Apply bias (-20V) and heater (or 15.5V and 4.5V across
filament if not center-tapped).

A triode (segment) will be off when its anode will be pulled low or when
its grid will be 5V more negative than the Cathode. The missing cathode
cutoff voltage means that the manufacturer does not assume reponsability
for remaining luminance when an anode is turned off.(but the contrast
factor will still be better than any LCD).

In my experience, with these values, the display will be so bright,
you'll need sunglasses to look into it. I am not joking. Reduce the bias
voltage (towards GND) to reduce brightness, or change the duty cycle.

Usually these are driven by custom display driver chips or open drain (p
type) drivers with pulldown resistors (to -Vcathode). You can also use PNP
arrays etc. The other way is to make the filament 'ride' on +5V (yours
truly once used the filament as limiter resistor for the zener that
supplied the logic), and provide +20V for the anode pullups. Then you can
run the system with open collector drivers that support 25V. Even ULN2803s
if that's what you are stuck with. Use a set of SIL resistor arrays for
the pullup/pulldowns, otherwise the part count will be terrible. Remember
that each segment is turned on by high on its grid AND on its anode. The
display will run fine (but darker) with Vbias as low as 18V (even 12V).

Peter

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2000\08\20@195633 by Jinx

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Thanks for the information. What had thrown me to some extent
was the claim by the vendor (not Futaba) that these displays are
"complete 5V operation". That would appear to be a rather large
portion of BS, with a side order, dessert and doggie bag. I shall
be speaking to them

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2000\08\20@201143 by David VanHorn

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face
At 11:57 AM 8/21/00 +1200, Jinx wrote:
>Thanks for the information. What had thrown me to some extent
>was the claim by the vendor (not Futaba) that these displays are
>"complete 5V operation". That would appear to be a rather large
>portion of BS, with a side order, dessert and doggie bag. I shall
>be speaking to them

Well, with the addition of a flyback converter to get the grid and anode
voltages (or grid and cathode)

Also, running the filament on DC is not healthy, even for the "dc" types.
They want AC, with the cathode current applied symmetrically to each end.
This is commonly solved with a center-tapped transformer winding for the
filament, but I've done it with an H-bridge, clocked by an anode signal, in
a multiplexed drive system. In this case, it was a retrofit, after an
afternoon at the futaba plant getting the real details on how to drive
them, and how NOT to drive them.

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2000\08\20@210937 by Jinx

face picon face
More helpful tidbits, thank you. Wish Futaba were more forthcoming
with what would seem to be simple and basic PS information.
I'm putting a web site together and amongst other things would like to
include practical circuits for all displays, including VFDs

From: David Van Horn

> afternoon at the futaba plant getting the real details on how to drive
> them, and how NOT to drive them

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2000\08\21@040434 by Caisson

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> Van: Jinx <spam_OUTjoecolquittTakeThisOuTspamCLEAR.NET.NZ>
> Aan: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Onderwerp: Re: [EE]:Fluorescent displays
> Datum: maandag 21 augustus 2000 3:13

Hello Jinx,

> More helpful tidbits, thank you. Wish Futaba were more forthcoming
> with what would seem to be simple and basic PS information.
> I'm putting a web site together and amongst other things would like to
> include practical circuits for all displays, including VFDs

I "retrieved" a VFD (?) off a machine to-be-scrapped, and could not find
anything on Futuba's site regarding it (It's a 2-line display, 5 volts
only, Reset, Clock & Data.  Contains a 8052 controller).  After a message
requesting data of the module I got a .PDF -file containing the full
details of the module.  The response took them less than a week !

If you are interrested, I could send you a copy.

Regards,
 Rudy Wieser

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2000\08\21@070100 by Jinx

face picon face
Yes, I'd appreciate that. At the time of purchase I scoured Futaba's
site for a PDF on my VFDs but it wasn't there. Customer service
did come good with a PDF after a request, but it's just a scan of
a bad copy of very scruffy engineer's diagrams, all in Japanese
except the table I mentioned the other day. Further requests for
info have not been answered and I'm assuming that's all they have.
For a company the size of Futaba I think that's pretty lousy. This
constant battle to get useful information on products is very tiring.
If it was commercially sensitive I could understand, but these are
components dammit.

> requesting data of the module I got a .PDF -file containing the full
> details of the module.  The response took them less than a week !
>
> If you are interrested, I could send you a copy.
>
> Regards,
>   Rudy Wieser

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2000\08\21@090650 by Olin Lathrop

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> Thanks for the information. What had thrown me to some extent
> was the claim by the vendor (not Futaba) that these displays are
> "complete 5V operation". That would appear to be a rather large
> portion of BS, with a side order, dessert and doggie bag. I shall
> be speaking to them

I agree their statement is misleading.  I think what they were trying to
point out is that all the CONTROL can be handled with 5V logic.  You can tie
the annodes to the 20V supply, and the rest is all 0 or 5 volts.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, EraseMEolinspam_OUTspamTakeThisOuTcognivis.com, http://www.cognivis.com

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2000\08\21@170945 by Peter L. Peres

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>5V, speak to them

Before you do that, make sure that the display does not completely go lit
and off when anode and grid are driven with only 5V ;) Some displays can
do that. Basically supply -20V to cathode and 4.5V floating to filament
thereon. Then, switch grids and anodes between GND and +5V. It might work
afaik. Some very sneaky tricks can be implemented in simple triode
type devices by just manipulating the distances and geometries of the
electrodes.

Peter

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2000\08\21@202917 by Jinx

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You and Olin have highlighted the grizzle I have about slack mftrs. Why
is it MY job to find out how their products work by experimenting ? After
1000's of design and production hours, surely a mftr can spare a bod
for a couple of hours to write up a publicly available document that will
assist customers. And then another couple of hours beating it into front
line staff not to ignore requests for that information. If they haven't got
it, tell me, don't just pretend I'm not here and hope I'll go away. Cos I
won't

> >5V, speak to them
>
> Before you do that, make sure that the display does not completely go lit

> Some displays can do that

> Some very sneaky tricks can be implemented in simple triode
>
> Peter

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2000\08\21@214303 by David VanHorn

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At 12:08 PM 8/22/00 +1200, Jinx wrote:
>You and Olin have highlighted the grizzle I have about slack mftrs. Why
>is it MY job to find out how their products work by experimenting ?

Because they have other customers with order quantities in seven figures.
 :0)


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2000\08\22@005920 by Jinx

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> At 12:08 PM 8/22/00 +1200, Jinx wrote:
> >You and Olin have highlighted the grizzle I have about slack mftrs. Why
> >is it MY job to find out how their products work by experimenting ?
>
> Because they have other customers with order quantities in seven figures.
>   :0)

Right now they have a customer with "one finger"

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2000\08\22@101515 by jamesnewton

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That is what the techref is for <GRIN>

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