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Fixing a Small Gotcha With Adafruit's NeoPixels
1/1/2014

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Phononscattering
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Product placement?
Phononscattering   1/1/2014 9:22:21 AM
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I'd like to point out that these so-called "Neopixels" are not a proprietary Adafruit product, but can be bought all over the web. The part name is WS2812 (6 pins) or WS2812B (4 pins) by worldsemi. (www.world-semi.com)
That said, these LEDs are really amazing.

David Ashton
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Addressing
David Ashton   1/1/2014 2:42:55 PM
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Max, you say that each pixel is individually addressable....but looking at your roll of them in the 3rd photo, along with your description of the Data in and Data out signals it seems to me that what happens is that you tell the first LED what colour you want, then when you tell it a different colour, it passes the previous settings on to the next LED, and so on.  Is that what happens?   Can you control the brightness as well as the colour (i'd imagine so....)

Very tasty goodies - as is the power adapter in photo 2.  I recently ordered some SMD mounting boards from Adafruit - had I known they had these I would have ordered a bunch of them as well.  Really handy.

 

Max The Magnificent
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Re: Product placement?
Max The Magnificent   1/2/2014 10:38:59 AM
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@Phononscattering: I'd like to point out that these so-called "Neopixels" are not a proprietary Adafruit product, but can be bought all over the web.

Very interesting -- thanks for sharing -- I see that you can get 100 of these little rascals as standalones for just $39 from eBay.

Max The Magnificent
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Re: Addressing
Max The Magnificent   1/2/2014 10:41:23 AM
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@David: Very tasty goodies - as is the power adapter in photo 2.

My chum Brian LaGrave pointed out that you can get these power adapters all over the place, but as I said to him, I'd never seen one before and I was on the Adafruit site after selecting the power supply and I was thinking "I really could do with a ... oooh, look at that!" LOL

Max The Magnificent
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Re: Addressing
Max The Magnificent   1/2/2014 11:15:40 AM
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@David: Max, you say that each pixel is individually addressable....

Well, perhaps I should have said "Gives the appearance of being..."

Adafruit provide you with an Arduino library, so a lot of the nitty-gritty details are hidden for you.

When you are creating a Sketch that uses these NeoPixels, first you include their library. Next you declare / instantiate a string of these pixels -- let's say we name it "strip" -- using a type of function call. One of the parameters to this call is the number of the digital output pin you are using to drive this string; another parameter specifies the number of pixels in the string (say 60).

One of the things they do for you is to set up an array in memory -- in th ecase of our 60-pixel stribg, you can visualize this as an array  0-to-59 of 24-bit color fields (8-bits each for the red, green, and blue components).

Now you can use one of their functions to set the values assocaited with individual pixels. For example:

    strip.setPixelColor(i, c);

Where 'i' is an integer of variable specifying the number of the pixel in which you are interested (0 to 59, in our case) and 'c' is the 24-bit color value.

Alternatively, you can use:

    strip.setPixelColor(i, r, g, b);

Where 'i' is the number of the pixel in which you are interested and 'r,' 'g,' and 'b' are 8-bit color values specifying the red, green, and blue components of that pixel.

The important thing to note is that using the strip.setPixelColor() function doesn't actually upload values to the physical strip -- it just changes the values in the array stored in your Arduino's memery. When you are ready to update the physical strip, you call the strip.show() function -- this streams (a copy of) all of the values out of the array in memory into the physical strip -- I think the way to think about this is sort of like a shift-register -- as you start shoving data in one end, it gets passed "bucket brigade style" down the strip -- but I'm not sure as to the exact mechanism.


Does this help make things a bit clearer?

 

 

 

David Ashton
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Re: Addressing
David Ashton   1/2/2014 2:44:12 PM
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@Max, thanks for that, makes perfect sense.  I think you are right about the shift register  analogy - it would seem that you can stream the data to the strip so fast that to the human eye it seems as if you're addressing each pixel.  (ie you could change pixel no 32 without changing the others, and stream the new data, and it will appear as if only that one pixel has changed).  Very clever, I can think of all sorts of effects you could do with these things.

Do you know how fast the data is sent?  (sorry, I'm one of those irritating people who likes to know exactly how everything works....)

Max The Magnificent
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Re: Addressing
Max The Magnificent   1/2/2014 2:53:19 PM
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@David: Do you know how fast the data is sent?

By some strange quirk of fate I do, because one of the parameters to their function is the clock rate and we checked that on the scope ... it's a 800KHz clock for the data stream to the strip.

David Ashton
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Re: Addressing
David Ashton   1/2/2014 3:01:03 PM
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@Max...some simple math reveals that a 1m string of 60 pixels will be refreshed at 800000 / 24 bits / 60 pixels = 555 Hz - surely too fast for the eye to see.  You'd have to get up to about 50M before you could discern any delay.  Very clever.

Max The Magnificent
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Re: Addressing
Max The Magnificent   1/2/2014 3:04:11 PM
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@David: ...surely too fast for the eye to see [...] very clever


It is way too fast for the eye to see and it's very VERY clever ... also you can have multiple strips -- each cointrolled by it's own Arduino pin...

Duane Benson
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Re: Product placement?
Duane Benson   1/2/2014 7:06:03 PM
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Adafruit sells products of their own design and products of someone else's design. What I really like about them is the amount of value that add to whatever it is they're selling. The libraries and tutorials they provide are pretty incredible in terms of quality and breadth. They also give a lot of support to what used to be a re-emerging hobby community, but is now also a re-emerging small start-up business community.

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