Neopixel Strip Pixels dying (?)

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

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rbutani
 
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Re: Neopixel Strip Pixels dying (?)

Post by rbutani »

I made a mistake. The "last pixel in the strip" is the first pixel if you look at the strip from the data in side. Sorry for the confusion.

Changing the number of pixels in software doesn't make a difference. Connecting the data line further down the strip also doesn't make a difference. The pixel starts to get hot the moment I plug the strip into the battery. (before data is even plugged in) Could my strip be defective?

Thanks in advance.

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adafruit_support_mike
 
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Re: Neopixel Strip Pixels dying (?)

Post by adafruit_support_mike »

Let me describe what I think you're saying to make sure I understand:

- The 'pixel gets hot' issue occurs whether you connect data to the strip or not.
- Only a single pixel (the first one from the data-in direction) gets hot.

rbutani
 
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Re: Neopixel Strip Pixels dying (?)

Post by rbutani »

That is correct.

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adafruit_support_mike
 
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Re: Neopixel Strip Pixels dying (?)

Post by adafruit_support_mike »

Okay, that's an interesting variant of a 'dead first pixel' issue we've seen recently. The issue itself is fairly rare given the sheer numbers of LED strips we sell, but there seems to be some combination of circumstances that will kill the first pixel in a strip.

The most common result is for the pixel to die completely, and fail to pass data along to the rest of the strip. Yours seems to have shorted in a way that allows it to continue working but run hot. It would be interesting to put the thing under a high-powered microscope to see exactly what happened, but for practical purposes it's dead and should be clipped off the strip before it causes worse problems.

If you can live with one less pixel in the strip, clipping the first one off should solve the problem. We can also exchange the strip you have for a new one.

rbutani
 
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Re: Neopixel Strip Pixels dying (?)

Post by rbutani »

If it isn't too much trouble, could I get the strip replaced?

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adafruit_support_bill
 
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Re: Neopixel Strip Pixels dying (?)

Post by adafruit_support_bill »

Not a problem. If you contact [email protected] with a link to this thread we can get a replacement out to you.

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grayconstruct
 
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Re: Neopixel Strip Pixels dying (?)

Post by grayconstruct »

I have used neopixels successfully in small quantity, powering directly from Arduino.
About to do a larger project, so will of course need a separate power supply for the LEDs and this is where things get complicated.

So you mentioned that you were powering your LEDs from batteries so power supply turn on/off spikes aren't an issue here.
So 3x1.5v batteries, thus 4.5v. The batteries may drain over time dropping lower until the point that the LEDs will no longer light, but my concern is in the input.

You are running the input line from an Arduino which is regulated at 5v.

If you look at the spec for the WS2812, http://www.adafruit.com/datasheets/WS2812.pdf
See that the maximum voltage is listed as +6.0 to +7.0 well, I would say keep it close to 5 to be safe.
See that the maximum input voltage is listed at -0.5 to VDD+0.5
This is typical of many IC's. You should not drive chip inputs higher than its supply voltage. (having to do with internal clamping diodes that protect the chip from static discharge). The internal gate could blow or the internal diode could short causing more thermal problems in the chip.
So it is even worse if the battery was disconnected entirely (0v) and the micro is still sending out data.
The best practices part of the guide now states to add 300 to 500 ohm resistor between the micro and pixel data in line, so this might solve the problem, but is it enough to completely protect the input diode/gate?

In my circuit, I think I might try an optoisolator on the data line just to be safe since either of the supplies may be off.

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