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Adafruit NeoPixel Eagle vs Datasheet [message #166795] Tue, 30 August 2016 17:40 Go to next message
gon says
Messages: 2
Registered: August 2016
Junior Member
/Hey guys,

I've a issue regarding the NeoPixel LEDs from Adafruit (+WS2812B+ +LEDs+).

In the datasheet of this LED model (https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf ​) it says that we should add a 0.1uF capacitor for each LED.

If you check the .sch and .brd for the NeoPixel Ring 24x LEDs (https://www.adafruit.com/product/1586 ) - +WS2812B+ -  we have 24 LEDs and only 15 capacitors (https://github.com/adafruit/Adafruit-NeoPixel-Ring).

I'm doing my own board with +WS2812B LEDs+. *Should I use 1 capacitor/LED -or- should I do as Adafruit and use 15 capacitors for 24 LEDs?*

​Thank you very much in advance!

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Re: Adafruit NeoPixel Eagle vs Datasheet [message #166796 is a reply to message #166795] Wed, 31 August 2016 09:45 Go to previous messageGo to next message
Jon Clift
Messages: 5
Registered: July 2016
Junior Member
If your own project is a simple personal one and you've got the space, put a 100nF with each LED and include a placement for some bulk decoupling [a tant or an aluminium electrolytic] where the power comes on to the board. That way you cover all the bases.

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Re: Adafruit NeoPixel Eagle vs Datasheet [message #166799 is a reply to message #166795] Wed, 31 August 2016 15:46 Go to previous messageGo to next message
Morten Leikvoll
Messages: 1343
Registered: November 2007
Senior Member
On 30.08.2016 19:40, gon says wrote:
> /Hey guys,
>
> I've a issue regarding the NeoPixel LEDs from Adafruit (+WS2812B+ +LEDs+).
>
> In the datasheet of this LED model (https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf ​) it says that we should add a 0.1uF capacitor for each LED.
>
> If you check the .sch and .brd for the NeoPixel Ring 24x LEDs (https://www.adafruit.com/product/1586 ) - +WS2812B+ - we have 24 LEDs and only 15 capacitors (https://github.com/adafruit/Adafruit-NeoPixel-Ring).
>
> I'm doing my own board with +WS2812B LEDs+. *Should I use 1 capacitor/LED -or- should I do as Adafruit and use 15 capacitors for 24 LEDs?*
>
> ​Thank you very much in advance!

This is really not an Eagle question, but general electonics development
question.

First, the WS2812B is a WorldSemi product. http://www.world-semi.com/
Their webpage may be a bit unstable since its hosted in Asia.

The datasheet RECOMMENDS one decoupling 100nF cap pr led, but this
doesnt necessarily mean its needed for it to function. The one cap pr
digital device is a good rule of thumb that you should follow unless
there is a very good reason not to. Adafruit's ring seems to have space
issues. Also they seem to keep the leds very close, so maybe they
decided it was ok to merge a couple. Maybe they have larger caps too, so
they can partly take the bulk function as well.

If you have long wires between the powersupply and the device, you'd
probably want a larger bulk cap close to where the power input is. These
LED's can draw significant power (~50mA pr LED), and you dont need many
to make the wire resistance cause significant voltage losses. When they
are all flashed at the same time at full white brightness, you have the
worst condition. You may want to test that.

If you don't know the expression decoupling and bulk and don't care,
just make sure you have wide power tracks throughout the path and add a
few caps here and there. Most likely you will have no problems unless
you have a mad number of led's.
Re: Adafruit NeoPixel Eagle vs Datasheet [message #167040 is a reply to message #166795] Fri, 09 September 2016 18:53 Go to previous message
gon says
Messages: 2
Registered: August 2016
Junior Member
Thank you very much for your answers! Now I understand why it is done the way it is :)

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