Author Topic: Pixel to Pixel distance using Cat5?  (Read 2763 times)

Offline CaptainMurdoch

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Pixel to Pixel distance using Cat5?
« on: August 05, 2015, 03:50:02 PM »
With all the talk about using Cat-5 for going from the controller to get further to the first pixel, has anyone done any testing on the max pixel to pixel distance when using Cat-5 instead of the flat 3-conductor wire?

I am planning on retrofitting some fence post cap solar lights with square node pixels but I think that the 8-9 feet wire-distance between the nodes will possibly be too far using the 3-conductor cable.  I am wondering if I could do it with Cat-5 without having to resort to null nodes.  uAmp's would be costly to implement for this use case.  I could do null nodes, but wiring would be a lot easier if I could just run straight from one light to the next with Cat-5.
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Chris

Offline corey872

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Re: Pixel to Pixel distance using Cat5?
« Reply #1 on: August 05, 2015, 08:03:06 PM »
You can try it, but I doubt the cat5 will make that much difference.  First the node data is not a 'balanced' signal, meaning you don't have equal but opposite polarity signals to transmit on the twisted pairs...you only have one 0-5V square wave signal.

What generally seems to kill that signal is the stray inductance and capacitance of the wire...which may actually be a bit worse on cat5 vs the 3 conductor.  The cat5 (or really, cat5e) might help a bit with reducing interference...assuming you ground both ends of the shielding...but there again, over such a relatively short distance, interference isn't of great concern...and grounding the shield may actually increase the capacitance of the wire and make the original issue of stray C and L even worse.

If you only need a few more feet, you might try making really solid ground connections.  The other major issue is when you run a lot of power and the ground line loads up.  (Think 'voltage drop', but in reverse) ...in the same way you might expect to have 12V at the power supply and it possibly dropping to 10V out at the nodes, the ground line is loaded to ~2V out at the nodes and drops to 0V on the trip power supply. The nodes can only reference data to what they see as a 'local' ground.  If the node is floating on a 2V ground, it may actually see the 0-5V data signal as a square wave alternating between +3V and -2V.  The node really doesn't care about the -2V, but really needs to see a signal over 3.5V on the positive side, so it can't read that data.

This is typically what causes "white lock up"...with white, you put so much power on the ground line, it floats up in voltage and the node can't reference the data signal to a good, solid ground. 

Info FWIW.

Edit - if you do go the cat 5 route, the best configuration is likely to be 3 wires for power, 1 for data, 4+any bare shielding wire (cat5e) for ground.
« Last Edit: August 05, 2015, 09:06:38 PM by corey872 »
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Offline gadgetsmith

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Re: Pixel to Pixel distance using Cat5?
« Reply #2 on: August 05, 2015, 08:10:44 PM »
Not sure what distances you are thinking about, but I plan to do some testing of this, with the biggest distance being about 15+ ft between pixels (end of one strand to another). I have three 50 pixel Christmas balls I'd like to run off one output of a yet TBD controller.

Offline Donny M. Carter

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Re: Pixel to Pixel distance using Cat5?
« Reply #3 on: August 05, 2015, 08:28:26 PM »
I will do some testing also. I need to separate some pixels between 4 columns. Would be nice if it works!

Offline JonB256

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Re: Pixel to Pixel distance using Cat5?
« Reply #4 on: August 05, 2015, 08:33:58 PM »
We're spoiled by the very strong data signal generated by the Falcon pixel boards. The puny little output amp in a Pixel chip just can't compare and can't handle big distance without a uAmp.

Offline Jeffl

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Re: Pixel to Pixel distance using Cat5?
« Reply #5 on: August 05, 2015, 08:59:48 PM »
I was testing 10' between the Candy Canes I'm building using the flat 4 wire (3 wires) I bought from HolidayCoro using a uSC and Hub as the driver and I didn't see any issues.  I'm not a pixel guru though so I my not know how to test.  Everything I threw at it looks good on the second string so far.

Offline CaptainMurdoch

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Re: Pixel to Pixel distance using Cat5?
« Reply #6 on: August 05, 2015, 09:21:49 PM »
Guess I need to do some testing with my actual pixels.  If I can get away with 9 feet of Cat5e then that should be enough to route the cable under the top rail that goes from post to post.

Offline RichM

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Re: Pixel to Pixel distance using Cat5?
« Reply #7 on: August 05, 2015, 09:31:22 PM »
One of my setups I have 4 candy canes in series, each using 10 ws2811 rectangle pixels( http://www.aliexpress.com/item/LED-digital-module-WS2811IC-5050-3LEDS-DC12V-input-waterproof-20pcs-a-string-256-gray-scale/578798417.html ).  I have a 10 foot extension cable between each cane using these from Ray: http://www.aliexpress.com/item/BLACK-3m-10feet-4-core-waterproof-extension-cable-one-end-with-male-the-other-end-with/1019827973.html.  There is also an additional 3 foot return run inside each cane using flat 3 wire.  Making the length between each cane 13 feet.  There are 3 extension cables and 15 feet to the first cane,  totaling a 54 foot run. The signal makes it across all 40 pixels just fine.

Hope this helps.  :)

Offline CaptainMurdoch

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Re: Pixel to Pixel distance using Cat5?
« Reply #8 on: August 06, 2015, 12:44:06 AM »
Thanks.

Offline zwiller

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Re: Pixel to Pixel distance using Cat5?
« Reply #9 on: August 06, 2015, 07:34:43 AM »
I thing the data distance is pretty forgiving but voltage drop, especially with the rectangular modules, is a whole nother ball o wax.  You need injection at every 20 modules or white really suffers.  I've since stopped trying to max out channels on a port.  Also, if you make a mistake with wiring power injection you fry modules.  Pretty easy to do with modules that several different wire schemes.  http://www.diychristmas.org/vb1/showthread.php?3260-RGB-module-mini-trees 
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Offline gadgetsmith

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Re: Pixel to Pixel distance using Cat5?
« Reply #10 on: August 06, 2015, 09:35:01 AM »
Completely agree with Sam.  I think the data line out of most controllers can go a decent distance, certainly better with twisted pair (even signal/ground twist is good).  Since i'm only a year 2 guy I don't have the knowledge and history to know where the 15ft distance limitation came from.

As a quick proof of concept I took a 20ft length of 20gauge 4strand bonded cable and ran it between string 1 and 2 of three connected strings (150 pixels total).  No issue with the data line, but certainly power drop is going to be an issue, especially since these are 5v pixels.  12v pixels will be far more forgiving.  If you run into power issues, you can certain use a higher voltage supply at the controller, and buck converters near the actual pixels.


Offline gadgetsmith

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Re: Pixel to Pixel distance using Cat5?
« Reply #11 on: August 06, 2015, 09:37:18 AM »
just another picture of the setup.



 

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