Power PixelBlaze via USB + 12v Strip (WS2815) independently?

I’m using WS2815 strips that run at 12v.

Can I power the strips from a 12v power supply and independently power the Pixelblaze from USB?

(This isn’t specifically covered in either the QuickStart or the Hardware Setup documents. It only mentions that “If you are using 12V LEDs, a separate 5V supply is needed for Pixelblaze.”, but doesn’t specifically say that a USB supply will work or not.)

Yes, but…

You may have data line issues, due to different ground levels. May.

Remember the PB generates the data line, even if the LEDs are powered by other means (in this case, 12v instead of 5v)

As confirmed by a quick google:
… the LEDs chips used in 12v strips (such as the WS2815) each contain an internal voltage regulator to provide a 5v supply to the chip’s logic.

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I would assume that I’d have to hook the ground connection from the strip to the PixelBlaze and that would be the common ground between the two.

That is effectively the same wiring as using an external 5V power supply with the 12V strips, right?

The internal implementation details of the strip is irrelevant. If I were to use power injection for a series of 5v strips – a separate supply for strip vs. PB – I’d still have a common ground.

The question here is can I replace separate 5V supply with the USB supply?

Or, I suppose, does the USB power share a common ground with the strip?

Yes, a USB power supply works the same as any other power supply. Negative/gnd is connected internally from the USB ground to the terminal ground so you don’t have to worry too much, just don’t connect +12v to the PB.

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Thank you!

Do you have some way to provide bug reports or feedback on the documentation? Are the docs in GitHub somewhere?

Happy to provide it, if so.

Sure!

You can also post on the forums, or send me an email wizard@electromage.com

Thanks!

And, btw, USB Brick + 12v externally supplied WS2815 w/only ground connected works perfectly!

(Off camera to the right is an ancient bench supply feeding 12v to the power injector connections of the strip. If you look closely at the picture, VCC is not connected from the strip to the PB. Note that I connected both data pins together to the DATA pin on the PB as this is a WS2815 w/redundant data pins).

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Could you make up a small step-down board from an AMS1117 or L7805 voltage regulator and maybe a filtering capacitor? If you’re not using the header pins, you could stick a female header on the underside of a piece of perfboard that isn’t electrically connected to anything and size it to bridge over to the top of the screw terminal block for mechanical stability. Then you could use the same 12V supply for both. N.B., I am not an EE some there may be more to it than I think, but it seems perfectly cromulent to me.

No need to make a board. Buck converters are cheap from your typical electronics mail order place. I picked up one that’ll happily do 12v to either 5v or 3.3v and will use that as the supply. Alternatively, a car USB wart would work, too, if I had one handy.

Some are adjustable. On a few, you can cut a trace on the back of the converter and then solder a jumper in another spot to select specific voltages!

https://www.adafruit.com/category/139


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