Author Topic: Introducing the Pi WS281x Pixel Board  (Read 967 times)

Offline lrhorer

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Re: Introducing the Pi WS281x Pixel Board
« Reply #15 on: February 18, 2019, 01:50:38 PM »
1)  I'm not familiar with any type of headers that would fit into that PCB.  Can you provide a link, or do you have a picture of what that looks like?
Um... 2.54mm (0.100") pad spacing is just about the most common there is, especially in legacy through-hole designs.  There are literally hundreds of different single row, 4-pin, 2.54mm headers and IDC connectors out there.


2)  S6 is labelled DI.  Yet it's the last port in the series.  Shouldn't this be labelled "DO" (data-OUT)?
The nomenclature is from the perspective of the pixels.  DI is the input to the first pixel in the string.  DO is the output from the last pixel.

3)  What ports have the u-Amp/f-Amp?  Each of the 6 ports have their own line-driver/amp?
No.  The amp only feeds S1.  If any additional repeaters are required, they will have to reside off-board.  I am not envisioning this to be used primarily in large-scale displays, so it is not designed to be very scaleable.

Here is the circuit board design - it may help:
« Last Edit: February 18, 2019, 02:17:29 PM by lrhorer »

Online Bwinter

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Re: Introducing the Pi WS281x Pixel Board
« Reply #16 on: February 18, 2019, 02:00:47 PM »
Yes, I understand that 2.54 spacing is common.  But I'm asking about what type of terminal connector (i.e. phoenix-type) that would fit in that space.


I don't think your usage of DI/DO isn't the standard nomenclature on boards.  When I see DO (data-out) on a board--that's where I'm expecting DATA to come OUT (of the board).


S1 has the uAmp, but the other's don't.  That's important info.

Offline lrhorer

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Re: Introducing the Pi WS281x Pixel Board
« Reply #17 on: February 18, 2019, 02:06:18 PM »
I've also not used these 4-pin strands (but I understand conceptually how they work).
I have, extensively.  In fact, of the 8300+ pixel elements in my Christmas display, all but 1000 or so are either these 4 wire pixels or an analogous DIY setup.

One question/concern:  is this return-signal buffered from each node as it makes its way back?
No, and that is a genuine design concern.  I've never had any issues, but then I have never hubbed any strings longer than 3 meters.
We all know that data straight off the WS2811 DO can only travel limited distance--and this is okay when one node is only 3-12" from the next one.  However, the "data-return" path on these strands can be quite long.
Yes, one must account for this very thing.  For moderate distances - perhaps 10 meters or so - a simple solution is to install an amp at the output of the last pixel on any long strings, rather than just looping the output back to the 4th pin.  One might even have to break into the return path along the way with an additional amp.  All quite easy enough to do.  As I mentioned, this is meant to be an inexpensive board for small-ish displays.  It can be scaled, to be sure, but scaleability is not designed into it.

Offline lrhorer

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Re: Introducing the Pi WS281x Pixel Board
« Reply #18 on: February 18, 2019, 02:14:49 PM »
Yes, I understand that 2.54 spacing is common.  But I'm asking about what type of terminal connector (i.e. phoenix-type) that would fit in that space.
IDC headers, fan connectors, etc.  Newark has almost 2500 of them.  Here is one:

https://www.newark.com/multicomp/2211s-04g/board-board-connector-header-4/dp/08N6746

I don't think your usage of DI/DO isn't the standard nomenclature on boards.  When I see DO (data-out) on a board--that's where I'm expecting DATA to come OUT (of the board).
Both are widely used.  Datacom tends to label a board relative to itself.  Telecom tends to label a board relative to the attached device.  Since I am a Telecom Engineer...

S1 has the uAmp, but the other's don't.  That's important info.
Fair enough.

Online Bwinter

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Re: Introducing the Pi WS281x Pixel Board
« Reply #19 on: February 18, 2019, 02:21:10 PM »
Thanks for clarification.

Offline algerdes

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Re: Introducing the Pi WS281x Pixel Board
« Reply #20 on: February 18, 2019, 02:55:29 PM »
Before I "knew better"*, I built a couple of pex trees (16 tubes) with 5 meter (~16 feet) WS2811 strips inside.  Each of the 16 strands on the tree had a data return from the far end that came back to the input end and then jumped to the next tube.  (Power injection was appropriately.)  These worked fine. 

Then again, I've had some strings of bullets that malfunctioned on a data return of about 8 feet.  Go figure.
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* "knew better"  = I was "taught" that this wasn't supposed to work.  If I had listened to those that "taught" me, I wouldn't have succeeded.
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BTW - Those same pex trees are going on their 6th year.
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Offline dkulp

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Re: Introducing the Pi WS281x Pixel Board
« Reply #21 on: February 18, 2019, 03:16:57 PM »
Dan, I was using pixelpuppy's numbers from Nov, 2018 - have the limits been back down in newer version?




See:  https://falconchristmas.com/forum/index.php/topic,10055.msg91149.html#msg91149


Basically, in theory, 800 should work, but in reality, it's not.    I still have no idea what's taking the extra 7ms. 


Dan


Offline mararunr

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Re: Introducing the Pi WS281x Pixel Board
« Reply #22 on: February 18, 2019, 04:34:46 PM »
Dan, I was using pixelpuppy's numbers from Nov, 2018 - have the limits been back down in newer version?

See:  https://falconchristmas.com/forum/index.php/topic,10055.msg91149.html#msg91149

Basically, in theory, 800 should work, but in reality, it's not.    I still have no idea what's taking the extra 7ms. 

Dan

 :D Thanks Dan!
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 This is just my opinion/suggestion/viewpoint.  Others with other viewpoints/experiences may have different advice.  I am a hobbyist with a couple years real world experience, not an expert.

Offline lrhorer

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Re: Introducing the Pi WS281x Pixel Board
« Reply #23 on: February 19, 2019, 01:25:52 PM »
I went ahead and changed the port nomenclature to DO for the pixel data input and Dret for the data return (from the last pixel output).  I am still *VERY* uncomfortable with putting the power leads on the outside pads of the string feeds.  It is just too easy to accidentally plug in a string backwards and blow not only the entire string but also potentially the power supply, since this board is not fused.

 

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