LED display for nightclub

Hey. That crazy idea came to my mind. At the moment we have 6 plasma screens in the club. I'd like to extend it with LED screen on the back wall of a stage. I don't need high resolution, I just want to play some simple low res animations. 96x64 pixels maybe. Because ws2801 LED strip is 32 pixels per meter. I thought I could use it, because it's not very expensive and there are already some ws2801 libraries available. But it would be nearly 200 meters of strip and 6000+ pixels. Is any Arduino capable of driving such screen? I know that Arduino can't produce those animations itself, because of limited memory. I was thinking about streaming video via artnet (or is there some simpler method?) and Arduino translating it to SPI signal. So maybe Arduino can be like a gateway? Is something like that possible? We already bought nearly 100 meters of ws2801 strip and it would be possible to try controlling it before permanent installation in furniture.

Greetings,

In addition to the strips you're going to need some beefy power supplies. I believe you need somewhere around 5-10 amps @ 5v per 5m segment.

Another thing to consider is that the signal will degrade as it travels through each WS2801 chip so you'll most likely have to have several different segments created of about 1000 individual pixels. The problem is the atmega368 doesn't have enough RAM to store all those RGB values in memory. I think you can only get away with about 250-300 before you run out. The Mega 2560 has 8 kb of ram, 4 times that of the mega368, but that still is only enough for about 1,000 pixels. So I don't think arduino is the approrpriate solution here. $2,000 worth of strips, probably around $500 worth of power supplies, and a $30 controller.. see what I'm getting at? But don't worry- there is still a great solution.

Enter embedded linux devices. This would be a great project for the Raspberry Pi or BeagleBoard. These devices have the capability to run the large kind of display you're thinking of. The Raspberry Pi UART goes up to a 250 MHz system clock and 31.25 Mbaud- now we're talking 6,000+ pixels. Coupled with the 512 mb of RAM and a processor with enough guts to process video and you've got the right tool for the job. The challenge will be more on the software side of things.

Keep us posted and good luck.

Of course the trouble of recommending R-pi to folks is they are still extremely hard to get. I put my name in on Feb. and paid for it, just recently, and I still haven't gotten the actual machine. I also suspect it will be at least 6 months or so before the infrastructure that exists for the Arduinos will be available for the R-pi.

Beagle board/bone, mbed, etc. are probably more realistic right now.

Well, if I remember correctly, the ws2801 takes 24 bits per pixel. I will work with your 100 meters for now. This is 3200 pixels. First of all, You do realize that this will take 192 amps to drive if you have every pixel set to white at full brightness? Do you have a way to supply power to this? Assuming you do, putting RAM and flash space aside for now, lets talk about SPI. With 3200 pixels at 24 bits per pixel, thats 76800 bits per frame. Since the arduino's max SPI rate is about 2,666,400 bits per second, all other arduino calculations aside, you could get about 35 frames per second. So there's some info for you

I ordered 12V WS2801 strips from factory. So it's little less amps than You calculated. I have a bunch of old ATX PSUs that I could probably use. Finding enough power is almost the easiest part. After ordering strips of course. I have read that WS2801 flickers when running long chains over 1-2MHz. And their maximum should be 25MHz. Could Raspberry Pi still run them at 250MHz? Could there be any other device that could drive that much strips? Artnet input -> multiple SPI outputs maybe? I have an artnet to 8x DMX device. DMX probably won't work. I could use 1 universe per 5m strip. So about 1000 pixels per 8 unverses. And I would need a bunch of dmx -> spi converters if there are any on the market. Are there any more options I could think of? How do they drive big LED displays anyway?

I wouldn't use ATX power supplies in a commercial application, although I suppose that could work unless the fire marshal sees it ;)

Here's a good source for some high quality power supplies http://www.trcelectronics.com/power-supply.shtml and more specifically http://www.trcelectronics.com/Meanwell/power-supply-pfc-hrp.shtml

I forgot how scarce those Pi's are. I just got mine in last week - been real fun so far. Now I'm tempted to try and get a ws2801 library working on it...

If you did find a Pi though you wouldn't be able to run the strips at 250 mhz, you'd still be limited to 20 or whatever the max is on the ws2801. Although it'd be lower as I mentioned before that the signal will degrade. So if you run it real fast over 1,000 pixels you might get flickering or inconsistent behavior. I just threw that number out there to drive home my point that it's way faster than the duino' 8)

Fortunately we don't have so strict laws that we can't use ATX PSUs. :D If You get ws2801 working on it, let me know. :P

PS: Just ordered my Raspberry Pi B. Should ship in 5 days.

holy crap! You already bought over 100 meters of that! Oh my lord!! Sorry, I have no advice but holy crap.

funkyguy4000: holy crap! You already bought over 100 meters of that! Oh my lord!! Sorry, I have no advice but holy crap.

Sorry, but... Y U so stupid?

If you don't mind me asking, where did you source the large order of WS2801 strips and what kind of pricing did you obtain?

I got mine from this seller on ebay ($107 for 5m) http://www.ebay.com/itm/WS2801-5050-Dream-Color-RGB-LED-Strip-5meter-5V-32led-meter-/260990314547?pt=LH_DefaultDomain_0&hash=item3cc43c2833

brs0906: If you don't mind me asking, where did you source the large order of WS2801 strips and what kind of pricing did you obtain?

I got mine from this seller on ebay ($107 for 5m) http://www.ebay.com/itm/WS2801-5050-Dream-Color-RGB-LED-Strip-5meter-5V-32led-meter-/260990314547?pt=LH_DefaultDomain_0&hash=item3cc43c2833

I bought from some Chinese manufacturer via alibaba.com. $11 per meter.

Ragnar:

funkyguy4000:
holy crap! You already bought over 100 meters of that! Oh my lord!!
Sorry, I have no advice but holy crap.

Sorry, but…
Y U so stupid?

Lol what? how did I become stupid from that? You are the one asking a question and frankly the stupid one for already buying 100 meters of expensive light strip without knowing how to operate them beforehand. As much as I hate flame wars and continuing them, this was just too stupid to pass up.

funkyguy4000:
Lol what? how did I become stupid from that? You are the one asking a question and frankly the stupid one for already buying 100 meters of expensive light strip without knowing how to operate them beforehand. As much as I hate flame wars and continuing them, this was just too stupid to pass up.

Ragnar:
try controlling it before permanent installation in furniture.

One should learn to read before coming on the internet.

I have controllers for them and I know how to operate them for what I bought them.
If it is possible to make a display out of it, then I order more. If no, then I’m not gonna buy anything.

Arduino Mega has 4 UARTs. Can use them for SPI?
I ccould control more LEDs.
But is it possible to use Arduino as a bridge between PC and LED strips? I could write a program on PC, which sends all pixels constantly to Arduino and Arduino sends them to WS2801. At the moment I have about 2000 pixels I could exercise on. They have dedicated controllers but I’d pull new cable to Arduino.
Arduino Mega2560 16AU - does its USB have enough bandwidth to drive 2000 pixels at reasonable FPS like about 25 from PC software?
I could also use artnet to send data to Arduino, but which option is faster and more reliable?

That is a very good question. I'd never thought about that. I looked around a little bit and I'd say, "maybe". UART is a hardware serial deal. SPI is more of a protocol thing. I don't fully understand it, I didn't read this whole thread, although I can gurantee you that the answer is in this thread.

http://www.edaboard.com/thread69740.html

No you need SPI ports of which none of the arduinos have to many of, some people have use soft SPI ports to get around this. Yes you can use it to bridge any of the USB to serial will be far to slow, DMX the standard for theatrical lighting is a higher baud rate than the arduinos can use to the PC for controlling 512 lights. Artnet get easily push the data rates your looking at for such low res stuff. A bunch of arduinos could get the job done but it's probably not the right tool for the job.

I understood that I could use USART port for DMX (RS485@250000baud). SPI is different deal. Arduinos have 1 SPI, also broken out on ICSP header.

I belive Arduino could make it to the 250000 baud rate necessary for DMX. Artnet is also DMX, but there could be maximum 256 DMX universes (each have 512 channels) running through ethernet cable.

I'd probably use artnet, but I need some example codes, otherwise I don't figure it out myself. I know that the code should be fast, if it's just a USB-artnet-WS2801 bridge.