Options for extending data signal range to Neopixels

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spectral
 
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Options for extending data signal range to Neopixels

Post by spectral »

Hi,

For my project I need to run neopixels around 15-20ft down from the Arduino that will be processing them. I am running 12v down this line for power, with 5v switching regulators on each side, but I just realized that the data line itself (3.3v from an Arduino Due) seems to lose reliability at these distances, resulting in flickering and other unwanted artifacts.

I have heard you can use individual Neopixels as repeaters, but this won't work for my purposes, as the line itself only has a 12v rail, and it wouldn't be practical to add regulators for each pixel repeater.

Instead, I feel I could instead use Adafruit's trinkets as repeaters, which can self-regulate the 12v, and are not even much bigger then a Neopixel. If possible, however, I'd like to avoid adding in this additional complexity (and cost) along the line.

My last idea, which is a bit of a shot in the dark, as I am new to all of this, is to use a NPN or MOSFET transistor to switch up the 3.3v data signal to 12v, then switch it back down at my strip. My understanding is that a 12v signal would easily pass this distance with less distortion, but maybe that is not the case. Before I attempt a prototype using this method, I thought I'd ask in here if this is a feasible solution, or if this would even help at all. Would a MOSFET transistor be able to switch a 12v line fast enough to emulate the low voltage signal, and to convert it back to 5v at the other end? Is there some other problem with trying to send a digital data signal at 12v?

Thanks for any help/advice!

- Eric

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spectral
 
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Re: Options for extending data signal range to Neopixels

Post by spectral »

It seems this: http://www.teknynja.com/2014/02/driving ... -over.html
Is the solution I really want, though most of it is over my head...

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zener
 
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Re: Options for extending data signal range to Neopixels

Post by zener »

Looks like a good solution. Which part don't you understand?

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spectral
 
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Re: Options for extending data signal range to Neopixels

Post by spectral »

Hi,

So I have been pursuing this method, and it is definitely less complicated then I previously anticipated, but now I have some questions about using twisted pair cables to send data in this method.

I can't use Cat5 alone, due to current requirements, as I am running around 360 pixels in total, in the form of 6 individual 60 LED strips (further referred to as a 'bulb') placed some distance apart, and all running as one continuous data line. My plan is to use 12 SN75176 transceivers, two on each bulb, one receiving from the previous one (or the arduino) and passing into the NeoPixel strip, and one at the end of the strip transmitting to the next bulb. Each bulb has its own 12-5v buck converter, and for wiring I am planning on sending a 2C 12AWG wire for main power transmission, paired with a 22AWG non-shielded twisted pair for the data transmission.

I have a few questions about this data transmission over twisted pairs, which is something I've never used before. Is there any problem pairing my 12v (~8A) power transmission line directly next to the twisted pair data line?

One requirement is that each bulb needs to be individually connectable, meaning the data path will pass in and out of plug-in connectors. I have 6pin PCI express power connectors that I am planning on using for this purpose (2 pin power, 2 pin data in, 2 pin data out). Is there any implications in passing the twisted line through a normal connector like this? Will this seriously degrade the signal quality? I believe I have read that as long as I keep the pair twisted immediately up to the connector, it might not be too bad? Another option is to put the transceivers on the other end of the connectors, meaning only the NeoPixel signal line is pass through the connector, but this means my transceiver circuitry is attached to my transmission line, not my NeoPixel 'bulb's which is a little more messy.

Also, something a little less important, what is the best way to pair two individually insulated wires to keep them together and not messy?

Thanks for any comments or advice, this is all very new to me!

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zener
 
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Re: Options for extending data signal range to Neopixels

Post by zener »

Since the power is DC you won't have any trouble with running the signal lines next to it. There won't be any potential for inductive noise coupling from DC.

The connector shouldn't cause an issue IMHO.

Why are you using 12GA for the power? If I read the Neopixel specs correctly they need 3.5A at 5V. So assuming your 12 to 5V converter has reasonable efficiency you would have less than 2 amps at 12V. In that case the example circuit you have, showing paralleling the extra CAT-5 pairs would work fine.

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spectral
 
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Re: Options for extending data signal range to Neopixels

Post by spectral »

I am running 6 60 strips in total, all over the same power line, so that would be a peak of 12A at 12V, though for my purposes I won't be exceeding 8A. Still too much for CAT5.

Thanks for your info, sounds like this might be a viable plan if I can pull it off :)

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zener
 
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Re: Options for extending data signal range to Neopixels

Post by zener »

This kind of stuff would be good for what you are doing:

http://www.sellntell.com/find_htm/pb.ht ... em&SK=1072

Only issues with this specific one is the minimum (1000 ft) and the 16GA is a little marginal for 8A probably. You could use it but it might get a little warm at 8A, and you would get a little voltage drop.

If you were using a lot (1000 ft again) you could have it custom made any way you want.

Maybe you can find some with 14 or 12GA in it. Good luck

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