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Topic: LED Strip white color turns into yellow at the end (Read 5405 times) previous topic - next topic

Jujup

Hey everybody,

I tried to operate a 5m long LED Strip (WS2801) with 160 LEDs. I am using a Raspberry, I know this is the Arduino Forum, however, I think it's the best place to receive a solution.
The Strip is operated with a 5V power supply. So far its no problem, I can swap between different colors. But when I use very bright colors, e.g. white (#FFFFFF), there is a color gradient from white to yellow/orange. This only occurs on mixed colors. Red, blue and green lights up correctly.

I've searched for this problem and could something that realy described my problem. I found infos about voltage drop, but I think this should only result in dimmed leds.

Attached is a picture of this. Do you have any idea why this happens?

By the way, if you wonder about the first LED.. I think it's a faulty one, because the blue part of RGB is always missing.

Thanks for any advice!
Jujup

Paul__B

#1
May 29, 2015, 05:18 am Last Edit: May 29, 2015, 05:25 am by Paul__B Reason: Always more to say!
No, it is in fact - absolutely - voltage drop.

if you measure the voltage at the end of the strip, you will find it markedly reduced.  Different colour LEDs have different threshold voltages, so reducing the voltage disproportionately affects the brightness of the different colours, especially - as you have found - the blue which has the highest threshold voltage.

You will need to provide a heavier "bus" cable for both Vcc and Ground and "drop off" these every forty LEDs (even better, every twenty).  Do not break the power lines in the chain, just connect the cable in addition to the supply points, it will then feed power both backward and forward from each "drop" point.

Lesson: The power strips in the Led strips are really quite flimsy.

By the way, if you wonder about the first LED.. I think it's a faulty one, because the blue part of RGB is always missing.
Perhaps, but it may be a blunder in the "tail" of the data stream.  Try adding one "dummy" LED to the end of the definition in the sketch and see what happens (I have not examined the protocol in detail, or indeed your attachment but suspect the first LED may be the last one sent).

Jujup

Unfortunately time was bare last year so I could start again with my project this year.
After connecting the power supply points every 8 LEDs everything works perfectly.

And yes, the first LED was definitly faulty.

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