Author Topic: Max Pixel Count - WS2811  (Read 3398 times)

Offline sth2258

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Max Pixel Count - WS2811
« on: January 18, 2017, 09:37:32 AM »
Is there a max number of 12v WS2811's that the PiCap can support? I've got a 1000+ pixel matrix that I want to dedicate to it

Offline mararunr

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Re: Max Pixel Count - WS2811
« Reply #1 on: January 18, 2017, 01:12:09 PM »
PiCap has two outputs that can support 800+ per output so you have plenty of room for 1,000 pixel matrix (may just want to split it and put 500 on each).
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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 sth2258

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Re: Max Pixel Count - WS2811
« Reply #2 on: January 18, 2017, 01:56:00 PM »
PiCap has two outputs that can support 800+ per output so you have plenty of room for 1,000 pixel matrix (may just want to split it and put 500 on each).
The site mentions "Can control two strings 800+ WS2811 pixels with fused and buffered outputs.", so wasn't sure if this was 800 total or per output.

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Offline jnealand

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Re: Max Pixel Count - WS2811
« Reply #3 on: January 18, 2017, 02:32:54 PM »
I take whatever is connected to an outlet/port to be one string.  for a megatree I use a string of 120 nodes which is physically two 60 node striings connected together.  In xlights it is 1 string of 120 with 4 strands since I go up 30 and down 30 and repeat, ie. zigzag.
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Offline gilv58

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Re: Max Pixel Count - WS2811
« Reply #4 on: February 11, 2017, 07:15:39 AM »
I take whatever is connected to an outlet/port to be one string.  for a megatree I use a string of 120 nodes which is physically two 60 node striings connected together.  In xlights it is 1 string of 120 with 4 strands since I go up 30 and down 30 and repeat, ie. zigzag.
Thanks
You have unintentionally giving me a better understanding on how to set things up.  There is much to be understood between physical connections. Physical node configurations. FPPP/PiCap set up and xLights channel setup.
Thank you for bringing a little bit of clarity into my understanding

Gil V


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Offline windsurf

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Re: Max Pixel Count - WS2811
« Reply #5 on: March 09, 2017, 01:07:25 PM »
OK, so now for a slightly different question...  Can the limit be increased from max of 1000 per output?  I have a wearable hat with 700 pixels.  Wanted to add a shirt with another 2000 or so.  That means i'm wearing 2 pi's and pi cap or pi and separate controller.  Doable, but it would be nicer if i could simply have the single device.
Proud owner of a 40', 32 Strand, 137 pixel per strand, 4,664 pixel (13,992 channel) Mega Tree!

Offline CaptainMurdoch

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Re: Max Pixel Count - WS2811
« Reply #6 on: March 09, 2017, 03:16:58 PM »
OK, so now for a slightly different question...  Can the limit be increased from max of 1000 per output?  I have a wearable hat with 700 pixels.  Wanted to add a shirt with another 2000 or so.  That means i'm wearing 2 pi's and pi cap or pi and separate controller.  Doable, but it would be nicer if i could simply have the single device.

The limit is totally dependent on the refresh rate.  You could go up to 2000 per output, but your refresh rate would probably need to drop to 100ms.  It takes time to send the data to the pixels and that is a fixed rate that can't be changed for WS281x pixels.
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Online dkulp

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Re: Max Pixel Count - WS2811
« Reply #7 on: March 10, 2017, 07:29:09 AM »
Another option could be to find an F4B and use that instead of the Pi cap.    It's got 4 outputs instead of 2 and with some creative use of a breadboard and jumper wires or similar could have a bunch more.   


Out of the box right now it's 600 pixels per output but on my DMX branch, I increased it to 999 per output. (the GUI prevents a 4 character entry field or I would have made it 1000)


Offline CaptainMurdoch

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Re: Max Pixel Count - WS2811
« Reply #8 on: March 10, 2017, 08:34:48 AM »
Another option could be to find an F4B and use that instead of the Pi cap.    It's got 4 outputs instead of 2 and with some creative use of a breadboard and jumper wires or similar could have a bunch more.   

Out of the box right now it's 600 pixels per output but on my DMX branch, I increased it to 999 per output. (the GUI prevents a 4 character entry field or I would have made it 1000)

We never actually tested the max number of pixels on the BBB, but wanted a safe limit at the time.  If you have tested a higher number then we can bump it up in the old UI as well.

Online dkulp

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Re: Max Pixel Count - WS2811
« Reply #9 on: March 10, 2017, 09:29:52 AM »


I've run 490 off of a single output on one of my BBB's without any sort of issue at all (my icicles).   I also set it to 999 with the last 500 pixels just being "junk" and the 490 displayed fine so I assume the 999 works fine.

Offline CaptainMurdoch

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Re: Max Pixel Count - WS2811
« Reply #10 on: March 10, 2017, 11:29:52 AM »


I've run 490 off of a single output on one of my BBB's without any sort of issue at all (my icicles).   I also set it to 999 with the last 500 pixels just being "junk" and the 490 displayed fine so I assume the 999 works fine.

OK, I added a note to my ToDo list to bump this up.  The most I had physically tested was about 50, but I did have the actual count set higher like you did and saw no issues.

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Re: Max Pixel Count - WS2811
« Reply #11 on: March 10, 2017, 11:50:55 AM »
OK, I added a note to my ToDo list to bump this up.  The most I had physically tested was about 50, but I did have the actual count set higher like you did and saw no issues.


Currently on my branch, with the 48string pru code, the absolute max would be 1041 as I only reserved 150,000 bytes for the string data and the rest for the serial outputs.  Using the 40string pru code, the max would be 1250.   We could likely increase the offset a bit more if more pixels are needed.    When I checked, the library managed to get 250K of shared memory and I believe the serial out maxes out at 32K (8x pixelnet).

Offline pixelpuppy

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Re: Max Pixel Count - WS2811
« Reply #12 on: May 02, 2017, 03:43:51 PM »
Can the limit be increased from max of 1000 per output?  I have a wearable hat with 700 pixels.  Wanted to add a shirt with another 2000 or so.
The limit is totally dependent on the refresh rate.  You could go up to 2000 per output, but your refresh rate would probably need to drop to 100ms.  It takes time to send the data to the pixels and that is a fixed rate that can't be changed for WS281x pixels.

For anybody who is interested, I did some quick math.  Based on 800Khz clock for WS281x and 300us reset for the 2813 (and newly revised 2811) at different refresh rates:

40fps = 25ms = 823 pixels per frame max
30fps = 33ms = 1101 pixels per frame max
20fps = 50ms = 1656 pixels per frame max
10fps = 100ms = 3323 pixels per frame max

These numbers are WS281x protocol maximums PER STRING (PiHat can feed 2 strings)
The pixel controller (FPP or other) may have other limits (memory and processing) that reduce these protocol maximums.
-Mark

Offline CaptainMurdoch

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Re: Max Pixel Count - WS2811
« Reply #13 on: May 03, 2017, 10:44:47 AM »
For anybody who is interested, I did some quick math.  Based on 800Khz clock for WS281x and 300us reset for the 2813 (and newly revised 2811) at different refresh rates:

40fps = 25ms = 823 pixels per frame max
30fps = 33ms = 1101 pixels per frame max
20fps = 50ms = 1656 pixels per frame max
10fps = 100ms = 3323 pixels per frame max

These numbers are WS281x protocol maximums PER STRING (PiHat can feed 2 strings)
The pixel controller (FPP or other) may have other limits (memory and processing) that reduce these protocol maximums.

Also, for anyone using those numbers, keep in mind that this is the max and there will be latency between the first and last pixel in the string.  The signal is regenerated at every pixel, so in the 20fps/50ms scenario, if you were able to use 1656 pixels, the first pixel closest to the controller would get its data and update 50ms sooner than the last pixel in the line.  That might not be a big issue for some use cases, but others such as a large matrix could appear slightly out of sync during some transitions or effects depending on the layout and wrapping used.  If you have pixel 1 sitting next to pixel 1656, there could be a noticeable difference or lag.

On the Pi, we limit to 1000 pixels per output in the config UI and this high limit is really only for the Pi v2 and v3.  The original B or other single-core models can't reliably handle this many pixels per output.

 

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