eazy - Tv - for - me

[timothyjackson]

Hello all

How difficult is it to build an LED screen, one which can recieve digital tv/video input?? I want to make a hugggeeee one...

anybody got any advice?

timbo

 

[evandude]

it would be about 90% wiring and 10% interface. do you know how many LEDs you would need??

for 640x480 resolution, assuming you want color display you would need 307200 pixels, at 3 LEDS per pixel thats 921600 LEDs. and 640x480 resolution would look terrible if it was a very big display. are you really prepared to buy almost a million LEDs? wiring them all up would take forever, not even considering the 1.8 million solder joints you would have to make... and how would you mount almost a million LEDs? going to sit there with a hand drill in a giant sheet of plexiglass and drill those holes?

for the interface you could probably find some sort of display multiplexing chips to actually drive the pixels... there'd be 1120 lines (row+column) so you'd need quite a lot of them. and then you'd need some video interfacing circuitry to drive the multiplexers.

i don't even want to imagine how much money this would cost you... even just buying almost a million LEDs, even assuming you could get them for a few cents apiece, would cost a small fortune...

and have you ever looked at a large monitor running 640x480 resolution?

try it on a 17"... or even a 19", etc. by the time you get it up to a matter of square feet in area, it's going to look terrible, you wouldn't be able to see much at all on it.

oh, and not to mention... even if you assume that only one of the LEDS from each pixel will be on at a given time (a very conservative estimate)
and you assume 10mA of current for each LED (again, conservative)
you're going to need some way of supplying 3072 AMPS of current to this display. good luck with that.

 

[JohnBrown]

So what exactly are you trying to say here? Would it be difficult or not?
:lol: :lol: :lol:

 

[bmcculla]

When you start to get into graphics sized displays they get expensive very quickly. Take 640* 480 thats 307200 pixels using RGB leds that 307200 LEDs. At 1 cent per LED thats $3072 and thats without any driving electronics or current limiting resistors.

 

[John Sorensen]

using RGB leds that 307200 LEDs. At 1 cent per LED

Where can I get some of them 1-cent RGB LEDs?

j.

 

[timothyjackson]

ok. i might stick with my black and white tv then.

In essence, I was trying to establish the reasoning behind companies charging large sums of money for LED screens. Now I know.

Anybody know of any companies selling large LED screens (for video) at the best prices?

1 cent rgb LED's? hmmm. are they cheaper in the US then?

Many thanks

Timbo

 

[Oznog]

So what exactly are you trying to say here? Would it be difficult or not?
:lol: :lol: :lol:

OK, simple answer: You will need to have a lot of experience in this specific field to make a driver, it will take thousands of dollars of LEDs, and development of the driver/board will take 6 mo-year IF you already know what you're doing. If you don't know, 5-10 yrs, if ever. There is no easier answer.

I certainly don't want to discourage you from doing a fun project- but look for something practical. Something like this won't get you a result and you probably won't have fun.

 

[JohnBrown]

So what exactly are you trying to say here? Would it be difficult or not?
:lol: :lol: :lol:

OK, simple answer: You will need to have a lot of experience in this specific field to make a driver, it will take thousands of dollars of LEDs, and development of the driver/board will take 6 mo-year IF you already know what you're doing. If you don't know, 5-10 yrs, if ever. There is no easier answer.

I certainly don't want to discourage you from doing a fun project- but look for something practical. Something like this won't get you a result and you probably won't have fun.

Sorry, I had my sarcastic hat on when I made that post.

 

[williB]

google 'RGB LED' lots of interresting stuff..this one is $1.79..

 

[bmcculla]

I was using 1 cent to show how expensive it would be - but then again if you bought 300,000 LEDs you probably could get a fairly good price.

 

[timothyjackson]

ok... stoopid question number two...

How does one connect up a rgb (or any other led with more than 2 legs)

I understand that normal leds have the power going in the cathode and out the anode.

(i so hope i have that right)

I got a bi/tri colour led.. and.. it ain't working - unsure how to connect it up.

Check here these guys out for cheap leds. www.hebeiltd.com.cn

low volumes. friendly.fast.

how connect up??

timbo

 

[evandude]

look at the datasheet for the one you are using. they are just several regular LEDs in one package. so powering them relative to the anodes/cathodes is the same... typically they will have separate anodes and all cathodes connected together (common cathode) to one pin, or vice versa.

 

[williB]

yeah they dont specify common cathode or common anode...


http://www.hebeiltd.com.cn/?p=led.rgb

how much was it??

 

[evandude]

if you have a multimeter it would only take but a minute to figure it out... put the negative lead on a pin, set the multimeter to diode measure mode... measure all the other pins, if all of them read a diode drop (a few volts for an LED most likely) then that's your common cathode... try all the pins, if you can't find a common cathode, try reversing the leads and looking for a common anode the same way.

 

[williB]

acording to the diagram the common is the shortest lead..

 

[zachtheterrible]

Anybody know of any companies selling large LED screens (for video) at the best prices?
Timbo

how bout a projector??

 

[timothyjackson]

Thanks for all your input..

i understand that bi/tri colour leds have common anode/cathode etc... I don't understand how to wire it up... e.g. does the + go to both cathodes? and 1 anode grounded?? does it switch between colours... or are both the colours emitted at the same time??

hmmm

projector... yes.. i did think of using projector. However, the problem is, I only have a 2 metre width space.... with a projector I need at least 2m of wide angle projection to get a large image, say 1 metre by 2 metre.... I thought LEd screens would be alot more versatile.

Any known companies who make these led screens, say 2 metres by 2 metres???

Many thanks

Timbo

 

[jrz126]

Common annode means it has a common + voltage supply. so when you connect a cathode to ground the corresponding color will turn on.
If you connect all the cathodes to ground, all the colors will light. (thats how it is for my bi-color leds, but Tri-color might be different)
Common cathode is just the opposite.


I dont really understand what you ment by the projector problem, but could you somehow use some mirrors to extend the distance of the projector? (I'm having a hard time focusing. I got up at 3 am to study for tests. so I'm kinda burning out right now)

 

[Nigel Goodwin]

Any known companies who make these led screens, say 2 metres by 2 metres???

I don't think you would want to know the price, assuming such things were available?.

How about a Plasma screen?, they are getting larger and larger.

 

[timothyjackson]

ok....heres a big question...

I'm gonna have a plasma tv,,, fixed,,, bolted up....secured on a trailer....don't ask me why.....

? .......how versatile are plasma screens......do they damage easily...i.e. bumps and bounces?????

can only find a 61 inche plasma....

TJ