LED stripes to build a screen - Feasability (Ws2801)

Hi Guys,

I'am totally new to LED with Arduino so I wanted to get some first impressions about my project. I want to build a more or less big LED Screen out of adressable LED RGB Strings with following dimensions: 20 Chains with 50 LED each. As it'll be use for all kinds of displays I need to be able to controll each LED indivitually. I found LED stings that can do it. Each LED is coupled with a small IC (Ws2801) with will be controlled by the Arduino with a certain protocoll. So my question is: How many Arduinos (Uno Or Mega or what ever you recommend) would be necessary to control all 20 Strings within a latency around 100-300 ms?

So that would be the first step of the project, later are more easy tasks to accomplish to add some interactivity to the screen.

Thanks so much in advance for your thoughts.

Cheers Niko!

Are you set on using the RGB LED strings? They make many kinds of RGB LED matrices such as this one that might be better suited for what you are trying to do. They automatically do multiplexing on the LEDs to save on power requirements and have a ton of other really useful functionality built in.

No need to re-invent the wheel, unless you have a specific need to use the RGB LED strings.

Thanks for the tip, but thats not going to suit the project as the screen is going to be more or a curtain. Wich will be spread in a hallway covering the left wall , the cieling and the right wall, so you.ll walk under some kind of LED tunnel....

Does anyone have expierience where to get the LED strings a cheap as possible? The Adafruit version in with 40 buck per 20 LED string way to overpriced..?!

Look at ws2812b string also, the control chip & LEDs are integrated together.
Altho latency will likely be less with ws2801 as it is driven more like an SPI device (that is missing chip select).
You can add some external gating and fake the chip select.
Or just blast out 20 strings x 50 LEDs/string x 3 bytes/LED = 3000 bytes in somewhat over 3000uS (3mS) with 8 MHz xfer speed and good coding, then wait 500uS (0.5mS) for the outputs to update.
Seems like plenty of time left for other processing in between 100-300mS updates.
Probably want a part with more SRAM, like 1284P with 16K, so you can be manipulating frames, or filling one while sending out, or similar.
I offer 1284P based boards in a couple of differetn form factors that make it easy to experiment.
http://www.crossroadsfencing.com/BobuinoRev17/
Example:

See the top project here:-
https://www.pjrc.com/teensy/projects.html

Should work fine, though you need 3K of ram just to fit the frame buffer (if you drive it all with a single device, which I would).

IMO: Use WS2812B strings if they're up against a surface, otherwise, you might want to go for WS2811-based ones with diffused LEDs, if you want them to be visible from all directions ( http://www.environmentalled.com/images/products/RGB.jpg - I do not endorse that overpriced source - just a pic of what I meant) - either way, they're dirt cheap on ebay, straight from our friends in china. Also - note that ebay vendors use WS2811, WS2812, WS2812B interchangeably, even though they are not the same part.

You will have to pay some attention to how you power your monster display - 1000 LEDs, at 20ma per color and 3 colors per LED, you're looking at 60 amps if you have em all at full brightness....

Wow thanks everyone for the great replys!

@DrAzzy: So about the power I.am not worring about that in the moment as only a very smart part of the screen will be alluminated at each moment. Can you explain the need of the ram and the buffer? So the arduino has less ram so I would have to add a chip or something?

So for the moment I"ll order 4 Stings @ 50 LEDs (Diffused) with WS2811 chip to create a first model of the project.

(http://www.aliexpress.com/item/promotion-12mm-RGB-full-LED-pixel-module-WS-2811IC-DC5V-input-50pcs-a-string-IP68-led/564836955.html)

Anyone ever had some experiences with Alibaba or Aliexpress here?

@CrossRoads:

Why do I need more SRAM? I don*t know what you mean by manipulating frames, It´s my second Arduino project so my experience is still limited! Wouldnt be the 16 Mhz of the Ard. UNO enough to drive the system?

Thanks for your help! I really appreciate it.

Cheers Niko

Why do I need more SRAM?

How much memory does it take to define the state of one pixel ( LED ) answer 3
How many pixels are you going to have? Answer 20 Chains with 50 LED each = 1000.
How much memory will will you need to define what is on your display? Answer 1000 * 3 = 3000 bytes.
How much memory does a UNO have? Answer 2048 bytes.
How much memory does a MEGA have? AnswerSRAM 8k bytes
Can you add extra SRAM to the UNO so that it works like internal SRAM? Answer no.

Haha okey thanks a lot that was well explained. So I will need at least an Arduino Mega to drive the 1000 LED.s Thanks!