Largest 7-seg LED displays?

"Tim Jackson" <tim@tim-jackson.co.uk> wrote in message
news:V5vyb.15172$lm1.121627@wards.force9.net...
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3FCA5168.C42039A@earthlink.net...
Tim Jackson wrote:

I was after large panel meters.
They quoted me about Ł500 UK each for 2" high voltmeters.

Tim

Two inch panel meters are not "Large" ;-)
--

Is this relevant?

Statement 1. They make large displays. As large as you like.
Statement 2. I happen to have had a quote from them for 2" high panel
meters.

These two statements are not connected except as guide to pricing, which
was
necessary because the company do not show prices on their website - you
have
to ask for a quote.

OK?

2" high is large as panel meters go. If you know where I can get them off
the shelf and cheap then I'd be interested in buying some. My customer
turned down the Ł500 quote. I can't build them myself any cheaper, my
time
is too expensive.
Tim
Click to expand...
OKAY... Put together a RFQ including and ---
How many?
what size display?
Voltage or current?
Provisions for how many ranges?
Resolution?
Environmental considerations?
Operating voltage?
Isolation requirements?

Would a Blue white display behind a polarized panel be OKAY?
OR Color preferred?
LED or?


Send to: astromation@pacbell.net

They will quote in USD. From what you suggest here, Less than $862 USD How
much? Fill in the data!
 
"Tim Jackson" <tim@tim-jackson.co.uk> wrote in message news:<V5vyb.15172$lm1.121627@wards.force9.net>...

2" high is large as panel meters go.
Click to expand...
I doubt that, because I have seen a great deal of 4", 6", and even 8"
panel meters on the market. In fact, your local repair garage likely
has quite a few of these on their diagostic and wheel alignment
systems.

Perhaps you don't really mean a "panel meter"?

Harry C.
 
"DaveC" <me@privacy.net> wrote in message
news:0001HW.BBEF4067000394A7F0080600@news.individual.net...
Would like to build a clock with very large display. I'd like 7 to 10-inch
high digits. The largest I can find is 5-inch.

I've considered doing a single LED array, but cost becomes an issue with
large digits.

Ideas? References?

Thanks,
Click to expand...
How about a small one with a big fresnel lens in front of it. Does it need
to be seen at angles?

Regards,
Bob Monsen
 
On Sun, 30 Nov 2003 22:12:25 -0800, Robert Monsen wrote
(in message <cZAyb.177913$Dw6.699406@attbi_s02>):

How about a small one with a big fresnel lens in front of it. Does it need
to be seen at angles?
Click to expand...
Hey, Bob. Creative answer. But yes, the display needs to be seen clearly at a
minimum of 45 degrees off-axis, more if possible.
--
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group
 
Joel Kolstad <JKolstad71HatesSpam@Yahoo.Com> says...

Come to think of it, seeing neon tubes switching on and off every second or
so all night long isn't that unusual...
Click to expand...
"Unlike incandescent or fluorescent lamps, neon tubes can be
switched on and off continually, or dimmed, without affecting
the lifetime."

http://www.signweb.com/neon/cont/neon101b.htm


Perhaps using cold cathode tubes would be much better then? As far as I
know, the whole point of having a hot cathode is to make starting (a whole
bunch!) easier -- with a sufficiently high voltage you should be able to
'jump start' the lamp directly, just as is done with neon tubes.
Click to expand...
That sounds like it would work.

"There is such a thing as a cold-cathode fluorescent lamp.
They resemble "neon" signs, but are generally of slightly
greater diameter. They are not too standard nor widely
available. They are also typically a bit less efficient
than hot-cathode lamps. However, they can be dimmed to
any degree without any chance of damaging them or causing
any excessive wear. It should also be noted that starting
these frequently does not cause any excessive wear. (If
excessive current flows during the first half-cycle of
operation, a generally insignificant amount of extra
wear occurs.)

There are also miniature cold cathode fluorescent lamps,
often used for backlighting LCD screens and in image
scanners. (LCD screens sometimes use other means of
lighting such as a white electroluminescent panel.)
Like the large ones, miniature cold cathode fluorescent
lamps are dimmable.

Many "neon" signs are actually a variation of cold-cathode
fluorescent lamps!

There are dimmable, electrodeless compact fluorescent
lamps generally known as induction lamps. These are now
available from electrical/lighting supply shops. These
use an even different way to get electricity from metal
to gas. These lamps work at a very high frequency,
which lets current flow capacitively through the glass
or use induction to get power from a coil to the mercury
vapor discharge. No metal electrodes touch the mercury
vapor discharge. These lamps should work at least
reasonably well with ordinary light dimmers."

http://members.misty.com/don/f-dim.html

(This page also has some discussion about heating the
filaments with a lower wattage. This might work for
flashing as well.)


--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/
 
"Roger Gt" <Xenot@pacbell.net> wrote:
"Joel Kolstad" <JKolstad71HatesSpam@Yahoo.Com> wrote:
How about using four foot long fluorescent tubes for each segment? :)

Why not? But the rate of display change would be slow.
Click to expand...
Not nessesarily. If you use relays in place of old-fashioned
starters, keeping them closed will keep the lamp off, and opening them
will allow the lamp to start instantly. [Dunno what that does to lamp
or ballast lifetimes, but flourescents _can_ switch quickly.]

--
William Smith
ComputerSmiths Consulting, Inc. www.compusmiths.com
 
Harry Conover wrote:
"Tim Jackson" <tim@tim-jackson.co.uk> wrote in message news:<V5vyb.15172$lm1.121627@wards.force9.net>...

2" high is large as panel meters go.

I doubt that, because I have seen a great deal of 4", 6", and even 8"
panel meters on the market. In fact, your local repair garage likely
has quite a few of these on their diagostic and wheel alignment
systems.

Perhaps you don't really mean a "panel meter"?

Harry C.
Click to expand...
I think he wants digital panel meters with 2" high seven segment
displays.
--
24 days!


Michael A. Terrell
Central Florida
 
DaveC wrote:
On Sun, 30 Nov 2003 22:12:25 -0800, Robert Monsen wrote
(in message <cZAyb.177913$Dw6.699406@attbi_s02>):

How about a small one with a big fresnel lens in front of it. Does it need
to be seen at angles?

Hey, Bob. Creative answer. But yes, the display needs to be seen clearly at a
minimum of 45 degrees off-axis, more if possible.
--
DaveC
Click to expand...
You can do it like some old scoreboards. Use a piece of thick red
Plexiglas. Cut it into strips for each segment, paint the sides black,
and drill holes in the back side for small lamps like the old 1847, or
the newer automotive side marker bulbs that push in. If you use four or
five lamps you can loose a lamp or two and still see the segment.
--
24 days!


Michael A. Terrell
Central Florida
 
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3FCB5134.8AFBD08D@earthlink.net...
Harry Conover wrote:

"Tim Jackson" <tim@tim-jackson.co.uk> wrote in message
news:<V5vyb.15172$lm1.121627@wards.force9.net>...

2" high is large as panel meters go.

I doubt that, because I have seen a great deal of 4", 6", and even 8"
panel meters on the market. In fact, your local repair garage likely
has quite a few of these on their diagostic and wheel alignment
systems.

Perhaps you don't really mean a "panel meter"?

Harry C.

I think he wants digital panel meters with 2" high seven segment
displays.
--
Click to expand...
To clarify. Earlier this year I was looking for industrial wall-mounting
digital meters to bolt on top of the machines that could be read at up to
about 20m, say from the production office or anywhere on the shop floor, and
would indicate the current value of a 0-10V process signal. I had in mind
multi-LED seven segment displays. Sure, wheel balancers, car park counters
and such, incorporate suitable displays, but they are built in, I can't bolt
them to the factory wall or connect them to the process. I was looking for
something installable by the resident electrician - a contractors bill for
panel building or interfacing would push the cost back into the stratosphere
(where accountants can't breathe).


Tim
 
<William P.N. Smith> wrote in message
news:qddmsv0bgcv1l2tlbbpi5hrk15260k8bc9@4ax.com...
"Roger Gt" <Xenot@pacbell.net> wrote:
"Joel Kolstad" <JKolstad71HatesSpam@Yahoo.Com> wrote:
How about using four foot long fluorescent tubes for each segment? :)

Why not? But the rate of display change would be slow.

Not nessesarily. If you use relays in place of old-fashioned
starters, keeping them closed will keep the lamp off, and opening them
will allow the lamp to start instantly. [Dunno what that does to lamp
or ballast lifetimes, but flourescents _can_ switch quickly.]

The lamps would work, but not always start reliably, since the off times
Click to expand...
would vary and the plasma path would cool at different rates. The ballasts
would be stressed, being current limited by inductance (assumption - not
electronic) but would run at full power all the time, thus reducing or at
least not improving life expectancy. If you were displaying data which
changed in minutes, the fluorescents would work just fine.... Readable for
a great distant.
 
"Guy Macon" <http://www.guymacon.com> wrote in message
news:58Odnfa0VtJt3FaiRVn-iw@speakeasy.net...
Joel Kolstad <JKolstad71HatesSpam@Yahoo.Com> says...

Come to think of it, seeing neon tubes switching on and off every second
or
so all night long isn't that unusual...

"Unlike incandescent or fluorescent lamps, neon tubes can be
switched on and off continually, or dimmed, without affecting
the lifetime."

http://www.signweb.com/neon/cont/neon101b.htm


Perhaps using cold cathode tubes would be much better then? As far as I
know, the whole point of having a hot cathode is to make starting (a
whole
bunch!) easier -- with a sufficiently high voltage you should be able to
'jump start' the lamp directly, just as is done with neon tubes.

That sounds like it would work.

"There is such a thing as a cold-cathode fluorescent lamp.
They resemble "neon" signs, but are generally of slightly
greater diameter. They are not too standard nor widely
available. They are also typically a bit less efficient
than hot-cathode lamps. However, they can be dimmed to
any degree without any chance of damaging them or causing
any excessive wear. It should also be noted that starting
these frequently does not cause any excessive wear. (If
excessive current flows during the first half-cycle of
operation, a generally insignificant amount of extra
wear occurs.)

There are also miniature cold cathode fluorescent lamps,
often used for backlighting LCD screens and in image
scanners. (LCD screens sometimes use other means of
lighting such as a white electroluminescent panel.)
Like the large ones, miniature cold cathode fluorescent
lamps are dimmable.

Many "neon" signs are actually a variation of cold-cathode
fluorescent lamps!

There are dimmable, electrodeless compact fluorescent
lamps generally known as induction lamps. These are now
available from electrical/lighting supply shops. These
use an even different way to get electricity from metal
to gas. These lamps work at a very high frequency,
which lets current flow capacitively through the glass
or use induction to get power from a coil to the mercury
vapor discharge. No metal electrodes touch the mercury
vapor discharge. These lamps should work at least
reasonably well with ordinary light dimmers."

http://members.misty.com/don/f-dim.html

(This page also has some discussion about heating the
filaments with a lower wattage. This might work for
flashing as well.)

Actually any florescent can be used as a CCFL by providing much higher
Click to expand...
starting voltages. Even so called burnt out tubes will light, although at
that late in life the output is much lower. The trick is to use them on
HVDC. The color changes too, so I haven't seen it done much!
 
On Mon, 01 Dec 2003 14:33:48 GMT, the renowned "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Harry Conover wrote:

"Tim Jackson" <tim@tim-jackson.co.uk> wrote in message news:<V5vyb.15172$lm1.121627@wards.force9.net>...

2" high is large as panel meters go.

I doubt that, because I have seen a great deal of 4", 6", and even 8"
panel meters on the market. In fact, your local repair garage likely
has quite a few of these on their diagostic and wheel alignment
systems.

Perhaps you don't really mean a "panel meter"?

Harry C.

I think he wants digital panel meters with 2" high seven segment
displays.
Click to expand...
Some years ago, I designed some with 3" displays but we found the
marketability to not be all that great. It's one of those things that
a lot of people *say* they want but when you go and make one, and
figure out how much it costs, many lose interest. There are up to
200mm (8") displays available, but the MOQ $, power required, PCB cost
and the housing cost goes up pretty fast at those sizes (with the
square of the height). Of course if you're actually into making
scoreboards..

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Roger Gt <Xenot@pacbell.net> says...

Actually any florescent can be used as a CCFL by providing much higher
starting voltages. Even so called burnt out tubes will light, although at
that late in life the output is much lower. The trick is to use them on
HVDC. The color changes too, so I haven't seen it done much!
Click to expand...
I wasn't aware of that. Thanks!
 
"Roger Gt" <Xenot@pacbell.net> wrote:
William P.N. Smith> wrote in message
"Roger Gt" <Xenot@pacbell.net> wrote:
"Joel Kolstad" <JKolstad71HatesSpam@Yahoo.Com> wrote:
How about using four foot long fluorescent tubes for each segment? :)

Why not? But the rate of display change would be slow.

Not nessesarily. If you use relays in place of old-fashioned
starters, keeping them closed will keep the lamp off, and opening them
will allow the lamp to start instantly.

The lamps would work, but not always start reliably, since the off times
would vary and the plasma path would cool at different rates.
Click to expand...
There is no "off" time, the tubes are either "ON" or in "Start" mode,
where the current through the filaments in the ends keeps them warm.
This is the old-fashioned 'short the ends to start the tubes'
paradigm, where the starter is a separate device....

--
William Smith
ComputerSmiths Consulting, Inc. www.compusmiths.com
 
In sci.electronics.design Guy Macon <http://www.guymacon.com> wrote:
Tim Jackson <tim@tim-jackson.co.uk> says...

"Guy Macon" <http://www.guymacon.com> wrote...

The seconds display would go through tubes rather quickly and
the tubes might have problems starting/stopping that fast,
depending on the ballast/starter design.

Fluorescent tubes normally switch on and off 100 or 120 times per second so
tube wear is not a problem per se. The trick would be maintaining the
electrode temperature during the off periods to get a hot restart. You
would need something a bit fancier than the typical snap starter to control
the heater current, but it wouldn't be particularly difficult to achieve.

That's an iinteresting idea, but I suspect that it wouldn't work.

The reason why the lamp restarts 120 times per second is not because
the electrodes are hot, but because the gas is ionized. The lower
left seconds segment is off for three seconds (digits 3, 4, and 5),
and the gas loses it's ionization in a fraction of a second. While
the electrodes are hot, they are being eroded. Keeping them hot won't
stop that from happening.
Click to expand...
What about cold cathode tubes?
I'm expecting delivery tomorrow of 2 CCFL tubes+drivers
(http://www.ebuyer.com/) for around $8(us) total.
 
"Guy Macon" <http://www.guymacon.com> wrote in message
news:naOdnZtur6WUPVeiRVn-vA@speakeasy.net...

The reason why the lamp restarts 120 times per second is not because
the electrodes are hot, but because the gas is ionized. The lower
left seconds segment is off for three seconds (digits 3, 4, and 5),
and the gas loses it's ionization in a fraction of a second. While
the electrodes are hot, they are being eroded. Keeping them hot won't
stop that from happening.


I am pretty sure that what erodes the electrodes is ionic sputtering. This
Click to expand...
is basically cratering of the cathode by impact of positive ions accelerated
by the end-to-end electric field. This process, and electron impacts at the
anode, are what keeps the electrodes hot when the heater turns off, but the
heavier positive ions do more damage (same energy (= e * electric field *
mean free path) but more momentum). I used to know all this stuff in the
days of valves (vacuum tubes) but I haven't revisited it for decades. In
high school at every opportunity I played with vacuum pumps and electrical
discharges.

Of course both the electrodes are alternately cathode and anode when using
AC supply, so both wear equally.

So to keep it running you need to supply a reduced heater current during
'off' to maintain the same heat input as the ion flow normally produces.
The rate of electrode ablation will certainly be reduced in the absence of
plasma current, not increased, so there is no abnormal ageing problem.

If the gas wouldn't conduct straight away then how would the lamp normally
start? We heat the electrodes to get electron emission, then apply working
voltage and "hey presto" it conducts and lights. With hot electrodes you
don't need any HV striking pulse like say a sodium lamp - try it, it fires
just like a neon lamp. Inverter driven fluorescents like for caravans don't
have any circuit for an HV pulse, they just fizz a bit then get brighter as
the electrodes heat up.

The gas doesn't have to be ionised to 'conduct' the electrons, they just
ionise it in passing, and while the gas is being ionised, it glows in the UV
as the battered atoms recombine and return to ground state. When the
current ceases the glow dies pretty instantly on a millisecond timescale, so
the excited population must have collapsed in that time. Most of the light
decay time ( a few ms) comes from the phosphor - the lower energy (visible
light) excitation states are longer lived.

You need a lot more current density for ionisation to make a significant
difference to conductivity. Think arc welder.

What we don't get at cold start with any metal-vapour tubes is full vapour
pressure, so we don't get full brightness for a while, and presumably a
somewhat higher striking voltage. Brightness might be a problem for the
7-segment display. You'd have to keep the tubes in a warmed enclosure to
get around it. Or use noble gas (eg neon) tubes like someone said.


Tim Jackson
 
Tim Jackson <tim@tim-jackson.co.uk> says...

I am pretty sure that what erodes the electrodes is ionic sputtering. This
is basically cratering of the cathode by impact of positive ions accelerated
by the end-to-end electric field. This process, and electron impacts at the
anode, are what keeps the electrodes hot when the heater turns off, but the
heavier positive ions do more damage (same energy (= e * electric field *
mean free path) but more momentum). I used to know all this stuff in the
days of valves (vacuum tubes) but I haven't revisited it for decades. In
high school at every opportunity I played with vacuum pumps and electrical
discharges.

Of course both the electrodes are alternately cathode and anode when using
AC supply, so both wear equally.

So to keep it running you need to supply a reduced heater current during
'off' to maintain the same heat input as the ion flow normally produces.
The rate of electrode ablation will certainly be reduced in the absence of
plasma current, not increased, so there is no abnormal ageing problem.

If the gas wouldn't conduct straight away then how would the lamp normally
start? We heat the electrodes to get electron emission, then apply working
voltage and "hey presto" it conducts and lights. With hot electrodes you
don't need any HV striking pulse like say a sodium lamp - try it, it fires
just like a neon lamp. Inverter driven fluorescents like for caravans don't
have any circuit for an HV pulse, they just fizz a bit then get brighter as
the electrodes heat up.

The gas doesn't have to be ionised to 'conduct' the electrons, they just
ionise it in passing, and while the gas is being ionised, it glows in the UV
as the battered atoms recombine and return to ground state. When the
current ceases the glow dies pretty instantly on a millisecond timescale, so
the excited population must have collapsed in that time. Most of the light
decay time ( a few ms) comes from the phosphor - the lower energy (visible
light) excitation states are longer lived.

You need a lot more current density for ionisation to make a significant
difference to conductivity. Think arc welder.

What we don't get at cold start with any metal-vapour tubes is full vapour
pressure, so we don't get full brightness for a while, and presumably a
somewhat higher striking voltage. Brightness might be a problem for the
7-segment display. You'd have to keep the tubes in a warmed enclosure to
get around it. Or use noble gas (eg neon) tubes like someone said.
Click to expand...
Excellent analysis, and much more accurate than my attempt was. Thanks!



--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/
 
DaveC wrote:
On Sun, 30 Nov 2003 22:12:25 -0800, Robert Monsen wrote
(in message <cZAyb.177913$Dw6.699406@attbi_s02>):

How about a small one with a big fresnel lens in front of it. Does
it need to be seen at angles?

Hey, Bob. Creative answer. But yes, the display needs to be seen
clearly at a minimum of 45 degrees off-axis, more if possible.
Click to expand...
Then how about a CRT with a purpose buillt driver? Even works in
the dark!


--
Graham W http://www.gcw.org.uk/ XP1800+ Page added, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.
 
"Roger Gt" <Xenot@pacbell.net> wrote in message
news:3Fxyb.62668$UP3.1845@newssvr25.news.prodigy.com...
"Tim Jackson" <tim@tim-jackson.co.uk> wrote in message
news:V5vyb.15172$lm1.121627@wards.force9.net...

2" high is large as panel meters go. If you know where I can get them
off
the shelf and cheap then I'd be interested in buying some. My customer
turned down the Ł500 quote.

OKAY... Put together a RFQ and ---
Send to: astromation@pacbell.net

They will quote in USD. From what you suggest here, Less than $862 USD
How
much? Fill in the data!

Tried that. As manufacturer they would only quote for an MOQ of 50 units.
Click to expand...
As and end user we only need a few. Hence the remark "off the shelf".
There's the rub.


Tim
 
"Graham W" <graham@his.com.puterINVALID> wrote in message
news:3C3zb.15857$lm1.126699@wards.force9.net...
Then how about a CRT with a purpose buillt driver? Even works in
the dark!


There's a thought.
Click to expand...

It would be cheaper than some of the options proposed just to buy a
last-year's-model PC on the surplus market and program it to display the
digits.

Not exactly the most reliable or energy efficient solution though.


Tim Jackson
 
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