Faulty Neopixel Strip

EL Wire/Tape/Panels, LEDs, pixels and strips, LCDs and TFTs, etc products from Adafruit

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n413
 
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Faulty Neopixel Strip

Post by n413 »

So I've recently purchased about 10 meters of neopixels(30 per meter), I havn't checked the two full reels yet, however the 2-meter portion doesn't seem to work. I have code that works properly on a different 2 meter strip that I purchased in a different order, the set-up is the same on both, a resistor(provided by adafruit) on the d_in pin and a 1000uf cap between the power.

On the new strip, when connected, sometimes it'll turn on fully (including the first pixel) but not change( as if it was stuck) othertimes random segments will be lit up and be random colors, but again not changing, but a good portion of the time nothing turns on at all, however when I unplug the power they all flash, including the first pixel. My best guess is that its the burnt first pixel problem, but i'm not sure considering i am able to get everything on occasionally

Also as as a side note i was wondering if it was safe to upload code to the arduino while the strip is plugged in and being powered?

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adafruit_support_mike
 
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Re: Faulty Neopixel Strip

Post by adafruit_support_mike »

It's safe to upload new code to the Arduino while the LED strip is connected. The microcontroller's pins all go to known states, and none of them do anything that should cause trouble for the LED drivers in the NeoPixels.

WRT the strip working intermittently, take a close look at the solder joints between the pixels and the pads on the strip. It sounds like you might have a marginal connection somewhere. That would be a manufacturing defect, so we'd probably want to swap a new strip for the one you have.

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n413
 
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Re: Faulty Neopixel Strip

Post by n413 »

Ah, thank you for answering that, its been bugging me for awhile.

It seems to display anything at random upon plugging it in and then holding that pattern(whether it be nothing or some seemingly random assortment of lights, might be dependent on code, but i'm not sure).

I can't see anything particularly wrong on visual inspection between the solder pads and LEDs. I COULD try to cut off the first LED and see if that's the issue. But if I do that and the rest still isn't functioning, would adafruit still be able to replace/refund it?

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Re: Faulty Neopixel Strip

Post by adafruit_support_mike »

The initial burst of random color is normal.

The WS2812B chips have built-in PWM controllers that contain a data register which they use to control the PWM rate for each LED. When you first apply power to the strip, the registers are in an undefined state.. thermal noise can produce random charges. The chip clears the register as part of the power-on process, but there's a short period between "have enough power to display the random data" and "have enough power to reliably blank the register".

The act of making and breaking connections can also generate noise that the chip interprets as data, and once the chip has data in its buffer it will continue to display that until told to do something else. We advise against hot-plugging strips in general. The noise-colors aren't too much of a threat, but voltage spikes can kill the first chip in several ways.

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n413
 
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Re: Faulty Neopixel Strip

Post by n413 »

Thank you for the insight.

From what I read, the capacitor is supposed to help with the voltage spikes, however if (somehow) the first LED/buffer is whats being messed up, can I cut it off, re-do the connections to the second LED and see if that solves the issue. or does it sound like that is not the problem at all?

If it is the entire strip which is defective, how would I go about getting it replaced?

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Re: Faulty Neopixel Strip

Post by adafruit_support_mike »

It's very unlikely that the whole strip is bad.

Each NeoPixel acts as a buffer for the rest of the strip. It consumes the first 24 bits it sees on the input pin, then passes everything else along to the next pixel. It eliminates a lot of problems inherent in managing long data connections, but if one pixel dies you lose signal to all the pixels beyond it.

We've seen several dead-first-pixel issues over the past few months. We still haven't isolated the exact cause, but our Best Practices list contains everything we've tried that seems to reduce the chance of another pixel dying. The one addition we're currently testing is to put a 10k resistor between DIN and GND where the signals connect to the strip. There's a chance that induced current in longer wiring could cause voltage spikes capable of killing the input pin. A 10k resistor to GND at the input will give any such current a safe path to follow.

Try jumping the input to the second pixel and add the 10k and see if that gets things working again.

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