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Author Topic: WS2801 - i2c channel problems (noise I believe?)  (Read 606 times)
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I've built some custom boards for my WS2801s to run some high power LEDs

https://www.sparkfun.com/products/10444
http://www.sparkfun.com/datasheets/Components/LED/WS2801.pdf

Running them in constant voltage mode, as per application example in the datasheet, in order to run these mommas (10w!) I have 5v and 12v running through my boards. Both are coming from a computer power supply I modified.

So far, it's been a blast!

Tested them individually, everything looked like it was working nice. But now that I've got a number of them strung up together through i2c, I'm seeing some intermittent flickering when color switching. Slowing my color animations down, reveals that the lights aren't switching to the right color sometimes, and the flickering gets worse the further down the line I go.

I'm not going to lie, I have these spread out over a number of connector wires that are pretty long, in total they run about 15 feet along 15 lights (a foot or so between each light). It seems that the data gets corrupt the further down the chain it goes. I'm not sure if this is due to attenuation because of wire length or if it's noise I'm introducing to the signal along each of the boards. My wire is 28 AWG.

I had some 0.01uF caps lying around, and put them on a few of the boards across the 5v and grnd, not sure if it made a noticeable difference, would it help to try caps with higher values like 1uF?

I guess what I'm asking for is a good way to diagnose what the problem is, or some common suggestions. I'm sure it could be a myriad of things and this may be a shot in the dark, but any suggestions would be highly appreciated!!
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Norfolk UK
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Maybe a few I2C repeater chips every 2 or 3 lights. Maybe something like this...
http://www.ti.com/lit/ds/symlink/pca9515a.pdf
http://www.nxp.com/documents/data_sheet/P82B715.pdf
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Dubuque, Iowa, USA
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I'd attack it with more decoupling caps. .1uF is the typical size to start with, but adding a 100uF near the power supply lines would be a good idea as well.
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