Reply by matt2-amstereo●December 30, 20052005-12-30
the worse display ive seen was one that used 4 leds per pixel 2red 1blue
1green. the best display ive seen used composite led's which were 5MM
led's with 4 di's per 'package' 2blue 1red 1green. 4 elements in a 5mm led.
if you wanted to you could bring the display down to VCD resolution
(350x288 or what ever the vcd res is), it wouldnt be HD or SD but still
perfectly usable.
Reply by MC●December 29, 20052005-12-29
Mochuelo wrote:
> On Thu, 29 Dec 2005 12:15:32 +1100, MC <MC@nonexistent.place> wrote:
>
>
>>>>Not a trivial or cheap project beyond around 150 x 40 pixles.
>>>
>>>Definitely.
>>>
>>>But wouldn't a 720 x 576 panel be one heck of a project!
>>
>>hmmm, that'll need around 4m x 3m of surface area if
>>you use 3mm leds.
>>Awkward for personal viewing, but if you don't close
>>the curtains then I'm sure that the neighbours will
>>appreciate it <g>
>>
>>I'll let you pay for the 240 Amps (peak) to run it.
>
>
> Where did you get that number from?
> If he uses 20 mA LEDs, and turns on one row at a time, the peak
> current would be 720*0.02=14.4 A. That is 43.2 W peak at 3 V. The duty
> ratio per LED would be 1/576. I would prefer 172.8 W and 1/144. A
> modern, high-brightness 3 mm LED produces a lot of light at duty
> ratio=1. At 1/144, probably one single pixel still produces more W/m^2
> at the eyes of an observer that is located at a distance such that
> s/he sees the 2.16 x 1.73 m (min) screen covering the same angle as a,
> say, 32" CRT display with only one pixel on.
eh ? what's wrong with a 2 orders of magnitude error ? <g> <g>
I assumed a non-multiplexed display to keep the brightness up
for outdoor use.
So 720 x 576 x 3 colours = 1244160 leds, and in the worst case
scenario they are *all* driven on at 20mA = 24.8 kA !!
>>And 3x 414720 high luminance Leds at (say) $0.10 each
>>comes to around $124k.
>>oh, you don't want a visible-in-daylight display ?,
>>fine, we'll use ordinary cheap Leds at $0.01 each
>>to reduce the price of the visible-bits to around $12k.
>
>
> Yes, price and self-"madeability" of this: horrible.
Reply by Mochuelo●December 29, 20052005-12-29
On Thu, 29 Dec 2005 12:15:32 +1100, MC <MC@nonexistent.place> wrote:
>>>
>>>Not a trivial or cheap project beyond around 150 x 40 pixles.
>>
>> Definitely.
>>
>> But wouldn't a 720 x 576 panel be one heck of a project!
>
>hmmm, that'll need around 4m x 3m of surface area if
>you use 3mm leds.
>Awkward for personal viewing, but if you don't close
>the curtains then I'm sure that the neighbours will
>appreciate it <g>
>
>I'll let you pay for the 240 Amps (peak) to run it.
Where did you get that number from?
If he uses 20 mA LEDs, and turns on one row at a time, the peak
current would be 720*0.02=14.4 A. That is 43.2 W peak at 3 V. The duty
ratio per LED would be 1/576. I would prefer 172.8 W and 1/144. A
modern, high-brightness 3 mm LED produces a lot of light at duty
ratio=1. At 1/144, probably one single pixel still produces more W/m^2
at the eyes of an observer that is located at a distance such that
s/he sees the 2.16 x 1.73 m (min) screen covering the same angle as a,
say, 32" CRT display with only one pixel on.
>And 3x 414720 high luminance Leds at (say) $0.10 each
>comes to around $124k.
>oh, you don't want a visible-in-daylight display ?,
>fine, we'll use ordinary cheap Leds at $0.01 each
>to reduce the price of the visible-bits to around $12k.
Yes, price and self-"madeability" of this: horrible.
Reply by Jasen Betts●December 29, 20052005-12-29
["Followup-To:" header set to aus.electronics.]
On 2005-12-29, Mark Haase <mehaase@gmail.com> wrote:
> In article <dovdbp$o4k$1@news-01.bur.connect.com.au>,
> MC <MC@nonexistent.place> wrote:
>
>> I'll let you pay for the 240 Amps (peak) to run it.
>>
>> And 3x 414720 high luminance Leds at (say) $0.10 each
>> comes to around $124k.
>> oh, you don't want a visible-in-daylight display ?,
>> fine, we'll use ordinary cheap Leds at $0.01 each
>> to reduce the price of the visible-bits to around $12k.
> Where on earth would you source 240 amps from? I don't have such a
> circuit in my house.
you could use a step-down transformer (etc), leds only need about 3V each,
or possibly run the LEDs in a number of series chains with transistors to
bypass individual leds (to make them dark(er)) and probably some sort of
switching regulator at the head of each chain..... and probably some sort of
custom IC doing all the switching.
if one IC can handle 10 leds 7680 ICs would be needed...
the IC could do PWM to modulate the brightness.... and only a little over
24A would be needed (at aroound 30V)
> Also, the time to fabricate, by hand, would be incalculable.
> My question is can the LEDs be operated in various intensities, or is it
> only full-off/full-on? If its it the latter, how do you produce gray? If
> its the former, how to you duty-cycle modulate millions of LEDs?
another way would be to matrix them with capacitors and scan at a
reasonable speed.
| //
+-->|--+-[R]->|--.
| | |
| === |
| | |
--|------+---------+-- ROW
|
COL
--
Bye.
Jasen
Reply by MC●December 29, 20052005-12-29
Mark Haase wrote:
> In article <dovdbp$o4k$1@news-01.bur.connect.com.au>,
> MC <MC@nonexistent.place> wrote:
>
>
>>I'll let you pay for the 240 Amps (peak) to run it.
>>
>>And 3x 414720 high luminance Leds at (say) $0.10 each
>>comes to around $124k.
>>oh, you don't want a visible-in-daylight display ?,
>>fine, we'll use ordinary cheap Leds at $0.01 each
>>to reduce the price of the visible-bits to around $12k.
>
>
> Where on earth would you source 240 amps from? I don't have such a
> circuit in my house.
This current would be at around the 3 (or so) volt level, so
you'll only need about 750W (peak) from the mains.
> Also, the time to fabricate, by hand, would be incalculable.
Not if you get it hand-assembled in China !
I once spend half a day populating and soldering a 256 Led panel. yetch.
> My question is can the LEDs be operated in various intensities, or is it
> only full-off/full-on? If its it the latter, how do you produce gray? If
> its the former, how to you duty-cycle modulate millions of LEDs?
To create colour, you need different intensities of the primary colours,
and the usual technique is to use pulse-width-modulation (PWM) because
it reduces power consumption and heat.
You'll also need colour correction of some sort because the Leds
you buy now will have different characteristics from the
ones you buy in 6 months time. (even if it's the same part number).
You can reduce this to some extent by buying a particular 'bin'
of tested and sorted devices, but the price then goes up a lot.
As to how to control millions of LEDs.., that I'll leave as an
exercise for you <g>,
but bear in mind that control and communication techniques which
work ok for a small number of pixels tend not to scale-up very
well when the numbers get into the realm of thousands of pixels.
Most sign manufacturers organise pixels in groups that can be
easily manufactured, installed and repaired as one entity.
eg. vertical strips of 2 x 16 pixels or 8 x 8 pixel panels,
etc etc etc.
Reply by Grant Edwards●December 29, 20052005-12-29
On 2005-12-29, Mark Haase <mehaase@gmail.com> wrote:
> Where on earth would you source 240 amps from? I don't have such a
> circuit in my house.
I think that was the point.
> Also, the time to fabricate, by hand, would be incalculable.
Long, yes. Incalculable, probably not.
> My question is can the LEDs be operated in various intensities, or is it
> only full-off/full-on?
Usually the latter. You can operate them at variable intensity
by varying the amount of current, but that's difficult. To
acheive "gray" you usually use pulse-width-modulation to vary
the duty cycle.
> If its it the latter, how do you produce gray?
Pulse width modulation.
> If its the former, how to you duty-cycle modulate millions of
> LEDs?
Good question.
--
Grant Edwards
grante@visi.com
Reply by Mark Borgerson●December 29, 20052005-12-29
In article <mehaase-AD0BBB.23450328122005@news1.east.earthlink.net>,
mehaase@gmail.com says...
> In article <dovdbp$o4k$1@news-01.bur.connect.com.au>,
> MC <MC@nonexistent.place> wrote:
>
> > I'll let you pay for the 240 Amps (peak) to run it.
> >
> > And 3x 414720 high luminance Leds at (say) $0.10 each
> > comes to around $124k.
> > oh, you don't want a visible-in-daylight display ?,
> > fine, we'll use ordinary cheap Leds at $0.01 each
> > to reduce the price of the visible-bits to around $12k.
>
> Where on earth would you source 240 amps from? I don't have such a
> circuit in my house.
240 amps at ~3V for the LEDs is only about 8 Amps at 110V. The power
supply shouldn't be that tough to build.
>
> Also, the time to fabricate, by hand, would be incalculable.
Not really---at least if you have a decent computer and Excel.
>
> My question is can the LEDs be operated in various intensities, or is it
> only full-off/full-on? If its it the latter, how do you produce gray? If
> its the former, how to you duty-cycle modulate millions of LEDs?
>
In article <dovdbp$o4k$1@news-01.bur.connect.com.au>,
MC <MC@nonexistent.place> wrote:
> I'll let you pay for the 240 Amps (peak) to run it.
>
> And 3x 414720 high luminance Leds at (say) $0.10 each
> comes to around $124k.
> oh, you don't want a visible-in-daylight display ?,
> fine, we'll use ordinary cheap Leds at $0.01 each
> to reduce the price of the visible-bits to around $12k.
Where on earth would you source 240 amps from? I don't have such a
circuit in my house.
Also, the time to fabricate, by hand, would be incalculable.
My question is can the LEDs be operated in various intensities, or is it
only full-off/full-on? If its it the latter, how do you produce gray? If
its the former, how to you duty-cycle modulate millions of LEDs?
--
|\/| /| |2 |<
mehaase(at)gmail(dot)com
Reply by MC●December 28, 20052005-12-28
>>
>>Not a trivial or cheap project beyond around 150 x 40 pixles.
>
> Definitely.
>
> But wouldn't a 720 x 576 panel be one heck of a project!
hmmm, that'll need around 4m x 3m of surface area if
you use 3mm leds.
Awkward for personal viewing, but if you don't close
the curtains then I'm sure that the neighbours will
appreciate it <g>
I'll let you pay for the 240 Amps (peak) to run it.
And 3x 414720 high luminance Leds at (say) $0.10 each
comes to around $124k.
oh, you don't want a visible-in-daylight display ?,
fine, we'll use ordinary cheap Leds at $0.01 each
to reduce the price of the visible-bits to around $12k.