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Have you ever had a great idea...

...that turned out to be a tad bit impractical? Well I had one yesterday. I was thinking about getting a new TV again and my train of thought arrived at the "Why isn't there a REAL LED TV?" - you see, the LED TVs that are sold have a LED backlight but just are regular LCD TVs otherwise. Still much better image quality but it's not like the pixels are LEDs.
So I continued: What if I get myself some small LEDs and solder them together? Should be some work but doable, right? Right!

But then I did some computations... lets say I want full HD - that is 1920x1080 pixels... and at clusters of 4 LEDs each (one of the colors has to be double AFAIK it's G-R-B-G) a pixel would be a 6mm square (assuming the smaller 3mm LEDs and no space between them) that gives me... about 11500mm... or 11.5m... damn! that will NOT fit in my living room... :( also it would take 8294400 LEDs... even at the bargain bins, that would be waaaay to expensive... not to mention the 16588800 soldering points. Yikes. And then, just for fun, I calculated that it would take 165888A at 20mA each to make the entire panel light up at once. Of course it would be pulsed IRL but still... damn, there goes my home-made LED-TV. What a bummer. Well, back to the drawing board.


( 3 comments — Leave a comment )
Jan. 24th, 2011 06:49 pm (UTC)
Muha. Let me put it this way: we Have this LED Screen in Berlin, it's resolution is 800x600 dots, if I remember right. Those "few" dots consume 80KW... average. The peak is about 107KW.

Besides of all the soldering points, think of the addressing. You want some kind of matrix. If you pick your LEDs wisely, you can get the same brightness with PWM but a lower power consumption then with non PWM methods. But on a screen of such a size you would not be able to get a clean picture. The wires would likely be too long (in the electrical way in context to the signals frequency) wich means reflections and a perverse EMI. So what you want is some industry-made LED panel with the LED crystals on a thin glass plate (and a biiiiig, noisy - and likely liquid based - cooling system on the backside) or an µC behind every dot, controlled via some fast twisted pair BUS.

Also, when done entrirely at home, and without special circuits, have fun with the sheer amount of processing speed you need to face the necessary picture processing and dot addressing.

But yes, if somewone would pay me for it.. sure, sounds like fun :)
Jan. 25th, 2011 12:11 am (UTC)
I have seen a report about a horse racing track viewscreen based on LEDs... they used 5mm ones in clusters of five for each pixel with space between. About 10*10 pixels formed a module with distinct controller circuitry. They were connected with the good old 5" floppy power connectors. Then they stacked those together to form a giant wall of a screen. I'd say about 50some meters long (the race horses took some time to pass it) and 4 meters high... But it wasn't a "flat screen" - the backside was several freight containers worth of cooling equipment :)
Jan. 25th, 2011 08:37 pm (UTC)
Ha, exactly. The display I mentioned is controlled by 6 cabinets, each man-tall, looking really heavy. Each is feed with an 5x16mm² cable. It's pretty cool but often makes me think about the energy it wastes :)
( 3 comments — Leave a comment )

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