Bad Neopixel strips

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zachr
 
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Bad Neopixel strips

Post by zachr »

A customer of mine purchased 25 meters of 60led/inch Neopixel strips. These were then cut into 10, 90" strips, and wired in pairs of two, such that power ground and signal were all shared between the two strips. (e.g. the same color information should be displayed on both strips in the pair).

Each pair was connected to Teensy 3.0 with an Adafruit level shifting board and powered off a 5v bench supply. I also put a 1000uF cap on each. All of the strips worked just fine for a bit. However, after several hours running simple color fades, I noticed two of the strips, in DIFFERENT pairs starting to display random flashes of wrong colors. After power cycling, those same two strips just turn either turn on full white or randomly flash colors instead of displaying the color fades that the other strips (which are wired in parallel) properly display.

I've tested the power supply voltage which has always been 5v or less. The fact that two totally different strips failed in similar ways is quite worrisome. These strips are supposed to go into a permanent installation and I am a bit worried that they are going to fail after some time. Is this a common issue? What do we need to do to get the failed strips replaced? I would need 180" of replacement.

Thank you,

Zach

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adafruit_support_mike
 
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Re: Bad Neopixel strips

Post by adafruit_support_mike »

That sounds like a problem with power distribution.

We recommend making VCC and GND connections every meter. The VCC and GND lines in the strips carry power well, but they do have a small amount of resistance.. all wires do. Any PWM system switches between "I'm drawing current now" and "I'm not drawing current now", and those sudden changes in current cause voltage drops across the resistance of the wire. When you get 137 LEDs switching up to 60mA each, the rails can become very noisy. Noisy rails interfere with signal propagation because the LEDs can't tell whether they're seeing a signal on the DATA-IN line or a spike on one of the rails.

Wires that carry power generally have much lower resistance than a PCB trace, and the power they carry is averaged out over several LEDs. The spikes tend to average out, and the remaining fluctuations in current don't cause as much change in voltage.

zachr
 
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Re: Bad Neopixel strips

Post by zachr »

I wish your explanation fixed the issue, but alas... The strips are damaged in some way and I need to get replacements ASAP. I went so far as cutting one of the bad strips down to just 24" and it still just lights up all white regardless of the values sent to it. Putting a scope on each of the lines shows that we are not seeing that much noise or spiking. A little ringing, but not that bad. Remember, I have 10 strips total all connected the same way, and most work.

Are you going to replace these?
Do I need to send them back?
What is the fastest way to proceed?

The only slightly suspicious thing that I have noticed is that there is a point in the cycling of colors where the strip pulls enough current to cause the power supply to current limit. This drops the voltage on the VCC line. Is it possible that this would damage the strips? If so, there should be a big warning about this.

zachr
 
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Re: Bad Neopixel strips

Post by zachr »

Because of our tight time frame, I have gone ahead and ordered replacement strips (order 400725). It would be great to get credit for the faulty strips.

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adafruit_support_mike
 
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Re: Bad Neopixel strips

Post by adafruit_support_mike »

The order has probably shipped by now, but we'll work something out.

Send a note to [email protected] with a link to this thread and the folks there will help you.

zachr
 
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Re: Bad Neopixel strips

Post by zachr »

Received my new strips. Cut and soldered up some replacement 90" strips and one strip turned all white the very first time I turned it on. Same controller, same power supply, same big cap as all the working strips. I even tried putting a series resistor on the data line (as I read in other posts), thinking this might revive it, but it's still dead. I now have a total of 6 dead strips out of the 20 or so I have purchased. This is VERY frustrating.

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adafruit_support_mike
 
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Re: Bad Neopixel strips

Post by adafruit_support_mike »

That has to be a signal problem. When NeoPixels fail, they don't do anything.

To get white, the bus has to be working, and every bit in the sequence has to be a 1. Each WS2811 buffers its input and sends a clean copy to the next one in the chain, so the point of failure is usually the first pixel in a sequence that doesn't do what it should.

Post a photo of your setup and connections, and we'll see if that tells us anything.

1chicagodave
 
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Re: Bad Neopixel strips

Post by 1chicagodave »

Just spitballing...

There are more links in this chain than just the NeoPixel strips. Since the replacement strips reacted the same way, the problem may lie elsewhere.
Things I would explore if I were troubleshooting this issue are...
  • Does strip act up when being run by itself?

    Does the pair of strips work properly when no other strips are connected?

    Which pins are you using as outputs to strips?
    - How many & which ports are those pins connected to?

    Which pins are 'bad' strips connected to?
    - Are they on same port?
    - Are those pins connected to anything else (LED? MINI54 mcu?)

    Try connecting them to different pins to see if that has an effect?
    ....try connecting to different pins on level shifters?

    How is power supply/noise to level shifters?

    Is there any other pattern or coincidence in usage between the two troublesome strips which may set them apart from the other strips which work well? (Colors, brightness, pattern speed...?)

    Is anything else connected to Teensy?

    Many pins have multiple uses/connections. Could anything else attached or running be affecting the specific data pins? (Similar to how USB may not function properly if certain pins are in use on some Arduinos.)
3.0 Pinouts
3.0 Pinouts
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pburgess
 
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Re: Bad Neopixel strips

Post by pburgess »

Do you have a plain vanilla Arduino Uno to test the strips with?

I've encountered the solid white phenomenon before...usually in conjunction with a board such as the Trinket where one must set up the system's clock prescaler to correctly operate at a certain frequency (e.g. the 16 MHz code is compiled but is then run on an 8 MHz chip).

Paul made some Teensy 3.0- & 3.1-specific changes to the NeoPixel library recently. Download the latest and see if there's any change in the result. If they're still wonky, I'd really suggest an Uno-based test to help narrow the troubleshooting gamut.

zachr
 
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Re: Bad Neopixel strips

Post by zachr »

Thanks pburgess! Changing the clock speed did the trick. On the Teensy 3.0 I was using 96Mhz. Dropped it to 48Mhz and strips that were failing before, started working again. Really weird that on most of the strips, it would work for a while, then consistently stop working. I would think if it were only a clock stability issue, that it would "sometimes" start working again. Something else is going on... however just glad to find a solution.

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