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Topic: Looking for an RGB LED addressable strip 1 LED per segment (Read 4 times) previous topic - next topic

KirAsh4

You clock the data in, the waiting period is to latch it in and thus the lights react.  You can clock data in all day long if you want, but it's not till you wait the 500uS that the data you clocked in will actually get latched in and the IC does something with the LEDs.

The FastSPI library takes care of all of that for you.

poodull

So reading this thread has me wondering:
http://arduino.cc/forum/index.php/topic,80567.0.html

why would you suggest WS2811 LEDs on an Arduino forum?  I would need a newer clocked arduino (uno, leo, teensy3, etc) to just keep up with >50 LEDs.  Specifically, something off-brand 'duino compatible with a honking processor.

Nobody on that thread mentioned fastSPI, though.  Is fastSPI fast enough to handle a 2811 on an 16MHz arduino?  32?  32 with interrupts? 

Your last post says 500us to latch, but the code says 50us... which the other thread says is impossible/flakey for more than a few leds.

I just seems to me like a pretty significant detail to skip, no?

fc

KirAsh4


So reading this thread has me wondering:
http://arduino.cc/forum/index.php/topic,80567.0.html

why would you suggest WS2811 LEDs on an Arduino forum?  I would need a newer clocked arduino (uno, leo, teensy3, etc) to just keep up with >50 LEDs.  Specifically, something off-brand 'duino compatible with a honking processor.

Nobody on that thread mentioned fastSPI, though.  Is fastSPI fast enough to handle a 2811 on an 16MHz arduino?  32?  32 with interrupts? 

Your last post says 500us to latch, but the code says 50us... which the other thread says is impossible/flakey for more than a few leds.

I just seems to me like a pretty significant detail to skip, no?


Go back and re-read it.  The original OP wanted to try the 2811, which is very different from the 2801 (and 2803 for that matter), and I suggested they experiment.  I wouldn't suggest the 2811 unless I've tried using them myself, and I have not.  As it turned out, you do need a faster processor to work with those.  A stock 16MHz/20MHz Arduino won't cut it.  The newer Leonardo might, but I have no bench test to prove that.  Nor do I have any interest in using the 2811s any time in the near future.  I'm quite happy with the 2801 and 2803, I've also ventured into the LPD1101 series (which is the next generation LPD6803).  They all work with FastSPI on a stock Arduino or clone.

You, on the other hand, are asking about the 2801, and you can drive those just fine with any stock or clone Arduino with a 16MHz processor, or even at 8MHz.  I have several strings that I made of 50 pixels, running on an 8MHz with no problems.  And I've bit-banged them, which is much slower than FastSPI.  I'm working on a custom design that has a 90 pixel string, running at 16MHz with FastSPI, no issues what so ever.

As for the latch/reset timing, read the datasheet, specifically page 11, under 'Gray Scale Data Word Format and Timing', very first sentence.  If you're using FastSPI, you don't need to do any of the latching yourself, just send it the necessary commands and the library does it all.  And those saying it's flakey, that's merely because they neglect to add the dataRate needed in the FastSPI code for this specific IC.

poodull

Okay, got it.  And let me start by first saying thanks for your help.  I really do appreciate it.

My only point of confusion (and the reason I posted my last post) was because the link you sent me to the led strip in Ebay states that it uses 2811s

http://www.ebay.com/itm/60-LEDs-m-1M-WS2811-RGB-LED-strip-IP67-Waterproof-Individually-Addressable-/160896346789

That's all.  I was confused because I think you found a similar strip to my link to Amazon, but with the different (faster) clock.

Or am I missing something bigger?

Thanks again,

fc

KirAsh4

#9
Nov 19, 2012, 09:06 pm Last Edit: Nov 19, 2012, 09:10 pm by KirAsh4 Reason: 1
Sorry, that's my bad.  I had multiple windows open.  What I meant to link was the 2801 version:

http://r.ebay.com/HUVgak

Note that the same vendor also sells a full reel, 5m, for a little over $144.  Buying it straight from China will be a little under $90 including shipping.  Just saying.

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