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Faulty NeoPixel Nano 3484
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Faulty NeoPixel Nano 3484

by JoeDrewn on Mon Aug 05, 2019 6:05 pm

Greetings ...

I purchased a batch of Adafruit 3484/SK6805-2427 nano NeoPixels through Digikey a couple weeks ago that are behaving erratically (flash on/off when commanded to turn on or don't come on at all). I replaced the 'faulty' NeoPixels with a batch purchased a couple months ago and they work fine. I noticed that the faulty NeoPixels all have a clear lens and the ones working correctly have an opaque lens. All part numbers and packaging are otherwise exactly the same for both batches.

Attached is a pic of the 'faulty' nano NeoPixel with the clear lens (purchased 7/25/19 from Digikey) and a pic of the 'working' opaque lens nano NeoPixel (note that the pic is taken from the Adafruit store but it looks the same as the previously purchased batch of nano NeoPixels that work correctly).

- Thanks, Joe
Attachments
NeoPixelNano3484_Good.jpg
NeoPixelNano3484_Good.jpg (401.2 KiB) Viewed 168 times
NeoPixelNano3484_Faulty.jpg
NeoPixelNano3484_Faulty.jpg (429.16 KiB) Viewed 168 times

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Re: Faulty NeoPixel Nano 3484

by adafruit_support_carter on Mon Aug 05, 2019 7:02 pm

Can you provide more info on the hardware they are being used on. A photo of how they are being used would help.

Also, what are you using to drive the NeoPixels?

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Re: Faulty NeoPixel Nano 3484

by JoeDrewn on Mon Aug 05, 2019 7:47 pm

It's a custom PCB (pic not available due to customer confidentiality). The NeoPixels are powered by 5v and driven by a pin on an STM32L4A6 thru a 74LVC1T45W6-7 level shifter with the output at 5v. A 470 ohm series resistor is connected to the DIN of the 1st NeoPixel (there are 3 NeoPixels daisy chained). The custom firmware driver uses timer driven DMA. Note that this is a proven circuit and firmware that has worked well using many different types of both RGB and RGBW NeoPixels (3484/SK6812-2427, 2659/SK6812-3535, 1655/SK6812, and 2759/SK6812-5050). The issue only occurs using the 3484/SK6812-2427 nano NeoPixels that have a clear lens purchased in the past few weeks.

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Re: Faulty NeoPixel Nano 3484

by JoeDrewn on Tue Aug 06, 2019 12:21 pm

Any updates on this issue?

I verified voltage levels and timing. Everything is well within spec according to the datasheet.
This issue is holding up production and will require a PCB redesign to implement alternative LEDs if a solution/workaround cannot be found.

Please reply with an ETA on options or a path forward. Contacting me directly via email and/or phone would be highly desired.

Thanks for your assistance.

JoeDrewn
 
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Re: Faulty NeoPixel Nano 3484

by adafruit_support_carter on Tue Aug 06, 2019 12:41 pm

No updates yet. I don't know directly, so have asked.

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Re: Faulty NeoPixel Nano 3484

by JoeDrewn on Tue Aug 06, 2019 1:46 pm

Could the 'faulty' NeoPixels actually be the newer SK9816-2427 (http://www.normandled.com/index.php/Pro ... d/848.html) instead of SK6805-2427? According to the manufacture pic (see attached) the die looks a little different but the lens is clear. More importantly, the control timing is slightly different. When I updated my firmware to use the different timing it appears to function properly.

Please confirm if the 3484 NeoPixels currently shipping are actually SK9816-2427. If so, please confirm if any SK6805-2427 remain in Adafruit or Digikey stock and/or if there are plans to ship them in the future. As you can imagine, supporting a mixture of both types across multiple products would be a significant burden for manufacturing and firmware.

Thanks for your continued assistance.
Attachments
NeoPixelNanoSK9816-2427.gif
NeoPixelNanoSK9816-2427.gif (70.19 KiB) Viewed 125 times

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Re: Faulty NeoPixel Nano 3484

by JoeDrewn on Tue Aug 06, 2019 4:09 pm

To clarify, I changed to control timing to T1H=900ns and T1L=300ns. However, I did NOT change the format to R-B-G with 16 bit dim at the end. I would expect the color to be wrong if this was in fact the SK9816-2427. So maybe this a SK6805-2427 clone with slightly different timing.

I look forward to more information.

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Re: Faulty NeoPixel Nano 3484

by jgrodin on Tue Nov 12, 2019 4:53 pm

SOLVED! We had the same issues. Different lens', same part number. Adafruit support insisted it's the same part when clearly it is not. We resolved the issue by changing the duty cycle for logic high from 50% (as specified in the data sheet) , to 75%. And it works with the "clear lens" and "opaque" lens 3484's. See attached for timing.
Attachments
LOGIC_TIMING_ADJUSTED.PNG
LOGIC_TIMING_ADJUSTED.PNG (12.39 KiB) Viewed 46 times

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