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Neopixel strip: data wire length issues
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Neopixel strip: data wire length issues

by ardtieboy on Sat Sep 25, 2021 5:33 am

Hi all,

I recently toyed around with a trinket m0 and an neopixel led strip (https://shop.pimoroni.com/products/flex ... 0032700499). I wrote some code, made a setup with my trinket, a small breadboard, some wires and my ledstrip and all was working fine.

When I was done prototyping I ordered a fresh trinket m0, soldered directly some wires on them (approx 2cm long) and attached the datawire, GND and USB wires to my neopixel strip (approx 20 leds). Result: nothing happened. I searched for more information regarding neopixels and saw you guys recommended adding a resistor to it (300-500 Ohm). I replaced the small data wire with a resistor, but still no success.

After some debugging, testing (and even ordering some new trinkets because I thought I messed mine up) I figured out that replacing the data wire from my trinket to neopixel with one that is longer (10cm instead of 2cm) solved my issues. I don't think it was a soldering issue as I had the same issue consistently for three of my brand new trinkets. My issue is now solved, but for further cases I would like to improve this (as now I have to somehow hide the long wire away in my final project). Any idea what is going on here? Where did I mess up? Afaics there is nothing described regarding the length of the datawire except they can't be too long?

Thanks for tips!
Ard

ardtieboy
 
Posts: 2
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Re: Neopixel strip: data wire length issues

by dastels on Sat Sep 25, 2021 2:22 pm

I suspect it was a soldering issue. Other than having wires so long that the voltage drop and RF interference become issues, the length is somewhat immaterial. There should be no difference between 2cm and 10cm. So either soldering, or a bad wire is my thought.

Dave

dastels
 
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Re: Neopixel strip: data wire length issues

by ardtieboy on Sun Sep 26, 2021 3:07 pm

Hi Dave,

Thank you for your post!

I’m however pretty convinced it was not a soldering issue. Here’s why:

When debugging the issue, I took my trinket with short data wire and put it inside a breadbord. In the same row, I put a small wire which was soldered to the DIN of my neoput. Again I got weird behavior (flickering, weird colors, only 3 leds working…).

Afterwards I repeated the same test, but put the data wire from my trinket in row A and the DIN of the neopixel in row B. I then made a bridge between row A/B with a wire of +-10cm. However then, all was working perfectly fine. I repeated this test (and previous one) multiple times in order to exclude that there was a cable loose. However the result was consistently the same.

Could it be that the data signal need some kind of clock signal which gets reflected if the cable is too short? Just shooting ideas here.

Ard

ardtieboy
 
Posts: 2
Joined: Sat Sep 25, 2021 5:25 am

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