Capacitor wiring in Neo Pixel projects

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rhizza
 
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Capacitor wiring in Neo Pixel projects

Post by rhizza »

Regarding this text from http://learn.adafruit.com/adafruit-neop ... uide/power
Before connecting a NeoPixel strip to ANY source of power, we very strongly recommend adding a large capacitor (1000 µF, 6.3V or higher) across the + and – terminals. This prevents the initial onrush of current from damaging the pixels.
Are there are any specific requirements, besides matching the polarity of the capacitor, DC power terminals, and Neo Pixel terminals, for the capacitor. Obviously, my inexperience shows because I'm mostly familiar with wiring in series and parallel. Based on the image Image
and reviewing numerous forum posts, it seems like the capacitor terminals and the Neo Pixel leads are just all joined together in the terminal. I'm just trying to confirm that this is true, or if I have to position the leads from the Neo Pixels in a particular way relative to the capacitor terminals. Does that make sense?

I have just purchased a few 35v 1000 uF capacitors for this step.

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adafruit_support_mike
 
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Re: Capacitor wiring in Neo Pixel projects

Post by adafruit_support_mike »

You want to connect the capacitor in parallel with the NeoPixel strip: positive lead to VCC, negative lead to GND.

In this case, the capacitor acts like a high-speed rechargeable battery. Its job is to swallow voltage spikes that appear in the VCC and GND lines.

All electrical signals involve current and voltage, and the event called a "voltage spike" involves a sudden change in the amount of current flowing through a wire. Positive spikes happen when you get a burst of extra current, negative spikes happen when there's a sudden drop in current.

Capacitors absorb current from positive spikes, and release current during negative spikes. That reduces the amount of change in current flowing through the wire, which in turn reduces the spike voltage.

It's the electrical equivalent of packing something fragile in bubble wrap.

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grayconstruct
 
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Re: Capacitor wiring in Neo Pixel projects

Post by grayconstruct »

This sort of transient load decoupling is just to reduce initial spikes on power supplies and smooth out ripple as the power supply tries to maintain voltage when the load changes abruptly from a large number of Neopixels. Typical power supplies already have these caps but by placing an extra one closer to the load might help more.

But yes, you just bridge it across the 5v and ground with the cap (-) connecting to ground.

And the resistor in series on the data line.

To learn more than you want about capacitors, check out the links at the bottom of the wikipedia page for Decoupling_capacitor.

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rhizza
 
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Re: Capacitor wiring in Neo Pixel projects

Post by rhizza »

Thanks for the replies! I have successfully powered this strip and a smaller 8 pixel strip too! Having a blast with these products!

Cheers!
Rhizza

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