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Discussion Groups | Comp.Arch.Embedded | Large 7-segment OLED

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Large 7-segment OLED - Viktor - 2006-12-02 13:07:00

Is there such a thing?
All I can find on the net are smallish alphanumeric and graphical
displays.

Thanks,

Viktor


Re: Large 7-segment OLED - Mike Harrison - 2006-12-03 08:00:00

On 2 Dec 2006 10:07:55 -0800, "Viktor" <v...@gmail.com> wrote:

>Is there such a thing?
>All I can find on the net are smallish alphanumeric and graphical
>displays.
>
>Thanks,
>
>Viktor

Why OLED instead of conventional LED?

Re: Large 7-segment OLED - Viktor - 2006-12-03 10:58:00


On Dec 3, 2:00 pm, Mike Harrison <m...@whitewing.co.uk> wrote:
> On 2 Dec 2006 10:07:55 -0800, "Viktor" <vkes...@gmail.com> wrote:
>
> >Is there such a thing?
> >All I can find on the net are smallish alphanumeric and graphical
> >displays.
>
> >Thanks,
>
> Viktor
>>Why OLED instead of conventional LED?

Power consumption.

>From what I've seen in the alphanumeric OLED datasheets, you get decent
visibility without backlighting. I was hoping to find single or several
digit displays to make a large clock module with only a few W
consumption.

I don't know if it's just a matter of time before these appear or if
there's a technology constraint in making large OLED segments. 

Viktor


Re: Large 7-segment OLED - Arlet - 2006-12-03 11:15:00

Viktor wrote:

> On Dec 3, 2:00 pm, Mike Harrison <m...@whitewing.co.uk> wrote:
> > On 2 Dec 2006 10:07:55 -0800, "Viktor" <vkes...@gmail.com> wrote:
> >
> > >Is there such a thing?
> > >All I can find on the net are smallish alphanumeric and graphical
> > >displays.
> >
> > >Thanks,
> >
> > Viktor
> >>Why OLED instead of conventional LED?
>
> Power consumption.
>
> From what I've seen in the alphanumeric OLED datasheets, you get decent
> visibility without backlighting. I was hoping to find single or several
> digit displays to make a large clock module with only a few W
> consumption.
>
> I don't know if it's just a matter of time before these appear or if
> there's a technology constraint in making large OLED segments.

>From what I've read, current OLEDs have lower efficiency than
conventional LEDs, so at the same brightness, a conventional LED should
have lower power.


Re: Large 7-segment OLED - Jim Granville - 2006-12-03 13:46:00

Viktor wrote:
> 
> On Dec 3, 2:00 pm, Mike Harrison <m...@whitewing.co.uk> wrote:
> 
>>On 2 Dec 2006 10:07:55 -0800, "Viktor" <vkes...@gmail.com> wrote:
>>
>>
>>>Is there such a thing?
>>>All I can find on the net are smallish alphanumeric and graphical
>>>displays.
>>
>>>Thanks,
>>
>>Viktor
>>
>>>Why OLED instead of conventional LED?
> 
> 
> Power consumption.
> 
>>From what I've seen in the alphanumeric OLED datasheets, you get decent
> visibility without backlighting. I was hoping to find single or several
> digit displays to make a large clock module with only a few W
> consumption.
> 
> I don't know if it's just a matter of time before these appear or if
> there's a technology constraint in making large OLED segments. 

  It's more likely simple economics - the market for jumbo LEDs is 
relatively tiny, (and primitive) and anyone developing OLED displays 
will chase the larger revenue streams first.

  How large a display are you after, on what power budget ?

-jg


Re: Large 7-segment OLED - Mike Harrison - 2006-12-04 03:31:00

On 3 Dec 2006 07:58:44 -0800, "Viktor" <v...@gmail.com> wrote:

>
>
>On Dec 3, 2:00 pm, Mike Harrison <m...@whitewing.co.uk> wrote:
>> On 2 Dec 2006 10:07:55 -0800, "Viktor" <vkes...@gmail.com> wrote:
>>
>> >Is there such a thing?
>> >All I can find on the net are smallish alphanumeric and graphical
>> >displays.
>>
>> >Thanks,
>>
>> Viktor
>>>Why OLED instead of conventional LED?
>
>Power consumption.

Are OLEDs actually any more efficient than standard LEDs for the same light output? I suspect
probably not. 
OLEDs typically compete with LCDs, which throw away at least 50% of th backlight light in the
polariser, and then about 60% mode in the RGB filters. Not hard to compete with that with a
light-emitting product. 
 
>>From what I've seen in the alphanumeric OLED datasheets, you get decent
>visibility without backlighting. I was hoping to find single or several
>digit displays to make a large clock module with only a few W
>consumption.

A few W will run a bunch of  (carefully chosen) normal LEDs pretty darn bright. 
And it will last longer - OLEDs still have some lifetime issues ISTR. 

Re: Large 7-segment OLED - Viktor - 2006-12-04 13:27:00


On Dec 3, 7:46 pm, Jim Granville <no.s...@designtools.maps.co.nz>
wrote:

>
>   How large a display are you after, on what power budget ?
>
> -jg

Thanks for the answers everybody.
I must admit, I've never actually seen a real live OLED so all my
information is hazy at best. I imagined it to be something like an LCD
with its own light source. So, I thought that in bright light it would
have a reflective component like LCDs (I've worked with some big LCDs
for petrol station pump displays and they are very good at high ambient
light.)

The largest 7-segment LED display I found (LITEON) had a 76mm digit
height and was stated at 30mcd/20mA.
With four digits, and about 20 segments, that would be about 5W. I can
just about manage that, but it wouldn't be at its brightest and it
would probably be poor in daylight.

So, is it just wishful thinking or do OLEDs have a reflecive function
like LCDs? 

Viktor


Re: Large 7-segment OLED - Arlet - 2006-12-04 13:40:00

Viktor wrote:

> On Dec 3, 7:46 pm, Jim Granville <no.s...@designtools.maps.co.nz>
> wrote:
>
> >
> >   How large a display are you after, on what power budget ?
> >
> > -jg
>
> Thanks for the answers everybody.
> I must admit, I've never actually seen a real live OLED so all my
> information is hazy at best. I imagined it to be something like an LCD
> with its own light source. So, I thought that in bright light it would
> have a reflective component like LCDs (I've worked with some big LCDs
> for petrol station pump displays and they are very good at high ambient
> light.)
>
> The largest 7-segment LED display I found (LITEON) had a 76mm digit
> height and was stated at 30mcd/20mA.
> With four digits, and about 20 segments, that would be about 5W. I can
> just about manage that, but it wouldn't be at its brightest and it
> would probably be poor in daylight.


5W for 20 segments @ 20mA doesn't sound right. At 1 Volt forward
voltage, the power is 20mW/segment, or 400 mW total. I don't know the
LITEON specs, but even if Vf is somewhat higher, you don't get close to
5 W.

Of course, if you add in the dissipation in the series resistor, total
power will be higher, but you can reduce that by using a lower drive
voltage made from a switching power supply (use a SimpleSwitcher for
instance), in combination with a smaller resistor.

If you multiplex the displays, you can use a higher peak current, so
the resistor can be even smaller, resulting in lower losses.


Re: Large 7-segment OLED - Viktor - 2006-12-04 14:03:00


On Dec 4, 7:40 pm, "Arlet" <usene...@ladybug.xs4all.nl> wrote:
>.5W for 20 segments @ 20mA doesn't sound right. At 1 Volt forward
> voltage, the power is 20mW/segment, or 400 mW total. I don't know the
> LITEON specs, but even if Vf is somewhat higher, you don't get close to
> 5 W.
>
> Of course, if you add in the dissipation in the series resistor, total
> power will be higher, but you can reduce that by using a lower drive
> voltage made from a switching power supply (use a SimpleSwitcher for
> instance), in combination with a smaller resistor.
>
> If you multiplex the displays, you can use a higher peak current, so
> the resistor can be even smaller, resulting in lower losses.

Six LEDs in series for each segment. The chart gives 20mA If @ 12V Vf.


Re: Large 7-segment OLED - Arlet - 2006-12-04 14:17:00

Viktor wrote:

> On Dec 4, 7:40 pm, "Arlet" <usene...@ladybug.xs4all.nl> wrote:
> >.5W for 20 segments @ 20mA doesn't sound right. At 1 Volt forward
> > voltage, the power is 20mW/segment, or 400 mW total. I don't know the
> > LITEON specs, but even if Vf is somewhat higher, you don't get close to
> > 5 W.
> >
> > Of course, if you add in the dissipation in the series resistor, total
> > power will be higher, but you can reduce that by using a lower drive
> > voltage made from a switching power supply (use a SimpleSwitcher for
> > instance), in combination with a smaller resistor.
> >
> > If you multiplex the displays, you can use a higher peak current, so
> > the resistor can be even smaller, resulting in lower losses.
>
> Six LEDs in series for each segment. The chart gives 20mA If @ 12V Vf.

Ah, I see..  that makes sense.

However, at 30mcd/20mA, these aren't the most efficient.  There are
single LEDs that are a few thousand mcd, at lower power. Perhaps you
can make your own display by taking some state of the art LEDs, and
mount them behind some diffusing plastic yourself ?


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