resistors and capacitors

jeffcrouse

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Dec 4, 2019
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I come from the world of Arduino/Neopixels, where best practice is to always put a 1000 µF capacitor across the power contacts and a 300 to 500 Ohm resistor between the Arduino data output pin and the input to the first NeoPixel.

But now I am using a fancy Advatek Pixlite MKII with some WS21813 pixels, and I'm wondering, is the resistor tip is still applicable? I was thinking maybe since the PixLite designed specifically for individually addressable RGB LEDs (unlike an Arduino), it's not needed.

I'm assuming the capacitor tip still applies since I'm powering the pixels directly from a Meanwell power supply.

Are there any other tips/tricks involving resistors/capacitors to cut down on noise in the data line? I saw something about this long ago, but I didn't get the full explanation.

Thanks!
 

keithsw1111

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Oct 11, 2012
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Kellyville, NSW
Resistor definitely not ... the Pixlite has a 30 ohm resistor built in and it is the perfect value for ws28xx pixels.

The capacitor is not necessary and is not there to help noise on the dataline but stop short duration power drops. Appropriate power injection will work fine.

Dataline noise is much less of a problem than power issues due to too much resistance on the ground wire. This is worse on 12V pixels. doubling up the ground or adding null buffers like the F-Amp fix that. The pixlite however has the best distance driving capability of any of the controllers on the market right now.
 

jeffcrouse

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Dec 4, 2019
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Thanks, Keith!

Just to be clear, I was talking about a capacitor on the power line not to eliminate noise, but to protect the strips from the initial power up. And you're saying that isn't necessary?

Great to hear I shouldn't have to worry about dataline noise with the PixLite.
 

AAH

I love blinky lights :)
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Adding a 300-500 ohm resistor to any output driving pixels is a godawful idea and the ONLY reason you would contemplate a resistance that high is if the chip driving the resistor has an incredibly low output current. WS28xx pixels should have a resistor in series with them in the range of 22-47R. If you go too high you will find that the distance that you can get with a null pixel, one of my Null Pixel Buffers and F-Amp or similar will be in the range of feet rather than a dozen to 100 yards that you should be able to get. The pixels themselves have a relatively low drive current so 10-12 yards is the max that you should get between pixels. The Null, F-Amp, u-Amp etc will in general have a high output current buffer in series with a low resistance resistor. This allows them to go dozens up to 100's of yards and maintain signal integrity.
I've never needed to and would never recommend putting a 1000u cap across the supply. If you are using anything like a decent power supply it won't be needed and in very rare cases you may see the power supply fail to start due to the excessively capacitive load.
 
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