Outdoor LED Screen teardown (+how to drive LEDs with video)

[unomasenelmar]

Wonderful, sublime, masterful explanation of his handling of an LED screen.

I think the design could be simplified, for example by integrating the LED driver and controller on the same panel LED will avoid excessive cable lines.

Congratulations for the job to explain and give these wonderful videos.

Greetings from Argentina.

Thank you.

[bigclivedotcom]

Very interesting. I wonder why they're changing it, since it isn't all that old. That said, the advances in LED panel technology over the past few years have been staggering, so the new display will probably just use off the shelf Chinese panels. I used to do the servicing on the vintage Scannervision display in Glasgow which used filament lamps with RGB filters in front of them to produce a low resolution colour display. The lamps were 12V xenon gas filled tungsten and switched with triacs.

[mikeselectricstuff]

@bigclivedotcom I guess LED wear-out - apparently it was originally installed 10 years ago, and had the panels replaced about 5 years ago. Olympics probably the excuse to replace. Don't know what they replaced it with, but doubt they'd risk cheapo panels for a high-rent location like this!

[bigclivedotcom]

@mikeselectricstuff I didn't realise it was ten years old. Time flies. The mass produced Chinese panels are not necessarily low quality things (I'm sure there are some though), LED video walls are so common now that a wide variety of breathtakingly slim and light panels are now available in surprisingly high resolutions. Ever go to PLASA at Earls Court? They always have a load of different systems on show, and it's rare to find any LEDs out on them these days.

[danalee1000]

I had no idea these were as complex as that, with regard to brightness levels. I just figured it was mostly pulse modulation. Thanks for another terrific teardown, Mike!

[coondogtheman1234]

Very interesting stuff. So is this unit yours to keep or do you need to return it? Also Is it possible to input an analog composite video signal via RCA connector into one of these units or a full screen? If so I could hook up a video game system to a display like this.

[mikeselectricstuff]

@coondogtheman1234 These were custom made for the London site, and not very useful for anything else, which is why I got one. You can't display normal video without a lot of pre-processing to format the data. 

[coondogtheman1234]

@mikeselectricstuff

isn't there a box or something that can convert the analog video to the format required by the array?

[mikeselectricstuff]

@coondogtheman1234 Yes. I suspect it's very expensive - if you can afford 6-7 figures for a big screen installation, 4-5 figures for the control box is small change....

[douro20]

Where I live there are a whole bunch of Optec LED displays, and they all use standard 5mm Nichia LEDs potted in marine grade epoxy. For a 25' wide highway billboard sized display, I understand that it takes four weeks to assemble the display and another to calibrate it. The video quality is fantastic; if set up and maintained properly you wouldn't be able to tell the difference from a regular paper billboard from a distance during the day.

[douro20]

But as for reliability, I would take a Daktronics display over an Optec any day.

[Mistamudd]

APART FROM... the need to use the dummy LED if you go for 1 red.

btw - you can prove this works... just look at off angle white with the shader on and then compare it to the shader off. You'll see the difference !

[mikeselectricstuff]

@Mistamudd I did look, and it only seems to make a difference at pretty extreme angles, though on a large screen I guess you'll have a range of view angles from most viewiing positions, and addiinig a little black lump doesn't exactly cost much!

[Mistamudd]

Another super teardown Mike. You are the Sherlock Holmes of the electronics world !

btw - the two RED / three RED question really comes down to the easiest way to make a good video White. You can use two reds running at medium intensity OR 1 red running at high intensity. Just so long as video white colour temperatures can be achieved, its 6 of one, half a dozen of the other....

[TheCrazyInventor]

Damn, there's a lot of complex engineering in those LED display panels. That was a very cool video. Thank you for showing us. :)

[ib9rt]

You mentioned 18 bits of intensity resolution, but what is the smallest change in intensity the human eye can discern? Is there any point going finer than that?

[mikeselectricstuff]

@ib9rt Not sure exactly, but even if your display data has 8 bits per colour, by the time you add global intensity control for ambient light compensation from sunlight to night-time, and enough resolution to do compensation for LED variations, you're easily over 16 bits.

[randomgarfield]

Nice tear down. I've serviced and worked with Barco's C11 and NX-6 LED displays before. It's interesting the differences. The Barco's tiles tend to have a lot more logic in the tile itself, and linking via DVI cables instead of SDI/HDSDI or whatever system those tiles use.

[ondraster]

Wow, cool... I am building something quite similar as a graduation project LOL. 32x48 bi-color (red & green) LED matrix.. Powered by ATmega128a with bunch of Allegro A6275's and MOSFETs to power each line... And connectable to PC through USB :)

[TheChipburner]

Very strange, but their pwm method is very cost-ineffective. It require one IC output per one LED. With multplexed LEDs it will require only one transistor for each row and one for each column, i.e. only 32 outputs to drive 16x16 matrix.

[mikeselectricstuff]

@TheChipburner No it isn't. These drivers are cheap - maybe 3 cents per LED. Using many drivers spreads the heat over a large area. Muxing would increase required bandwidth, increase peak LED current which may reduce lifetime, and increase flicker (e.g. when viewed via a video camera). 16x multiplex would never get near the maximum LED brightness.

[MMGWsceptic]

@mikeselectricstuff Seconded. The LEDs in this product are driven at about 20mA to get 5000cd/m2 brightness. LED efficiency and lifetime drop with currents so even with 4:1 mux you may need > 100mA peak current to achieve the same brightness (since you'd have 1/4 the time to light up each LED). So the muxd LEDs would die quick. Also - the drivers would get too hot since they'd be pumping out 100mA all the time.

[aDaWaN]

Awesome video's mike! Really like all the technical stuff you do, great entertainment for an Electronic Engineer.

[aerofart]

Nice . . .

[First2ner]

what do you use to see this signals?

[mikeselectricstuff]

@First2ner Agilent MSO6034 scope, with external monitor

[Gameboygenius]

Two red LEDs? I've heard about panels with two greens LEDs per pixel to increase the green resolution (because that's what our eyes are most sensitive to.)

[mikeselectricstuff]

@Gameboygenius It's quite a while ago but I'm fairly sure it was 2 reds.

[Films4You]

Some beafy Resistors 3:30

[Chryseus8086]

Awesome video Mike I love the detailed explanation !

[BeJ95]

Fantastic tear-down! Love the external cro monitor show ;) Well done Mike!

[MrGerbilBrain]

now could you make an RGB LED cube with all those LEDs? that would be cool! :D

[superdau]

@MrGerbilBrain

No. The LEDs are potted in epoxy mounted on an opaque board. What use would making a cube be, when you can't even see the inside?

[zzzzbest]

Nice video, good detail about the LEDs are driven.

How would that conformal coating around the LEDs be applied without getting it on the LEDs themselves?

[orbiter8]

You really know your stuff Mike. Excellent video

Thanks