Neopixel strip flashes on for a moment then stays off

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squeakyneb
 
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Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

I've got an arduino running the strandtest example code. It's wired as the uberguide shows, with a 4700 uF cap and 330 ohm resistor. When I power the strip, it flashes on very briefly and then goes out.

During fiddling (trying to solve the problem), I did get the strip to work fully and as expected. I had to resolder a power wire that I was holding in place, after which the problem came back. I have no idea what has changed.

The strip has previously worked fine. I used it with an adjustable desk-top supply set at 5 volts for a while. The strip's been sitting on my shelf most of this year. I bought an Adafruit 5V 10A supply and got the strip back out and that was when the problem started. My old power supply doesn't make it work any differently to the new one. The brief period where it DID work was with the new power supply.

I don't think the new supply burnt them out, because it did drive them successfully for several minutes (at least) in the midst of troubleshooting.

I'm confused as hell at this point.

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adafruit_support_bill
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by adafruit_support_bill »

If you post some photos of how you have it all connected we will take a look.
I had to resolder a power wire that I was holding in place
Intermittent power connections are dangerous to Neopixels. Applying a signal to an un-powered or intermittently powered strip can cause damage. The same caution applies to the ground wire. As noted in the Uberguide, to avoid damage, the data line should always be the last thing connected and the first thing disconnected.
https://learn.adafruit.com/adafruit-neo ... -practices
Avoid connecting NeoPixels to a live circuit. If you simply must, always connect ground first, then +5V, then data. Disconnect in the reverse order.

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squeakyneb
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

Photo attached. The yellow/brown line is the data line (330 ohm resistor hidden under the heatshrink). The black line has nothing but a solder joint under the heatshrink in the middle, I just extended the line. The white lines are the power lines. The strip is connected under the heatshrink in the lower right of the image, nothing there's changed since the strip last worked.

If the strip is broken, why would it go from broken to working and back again?
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adafruit_support_bill
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by adafruit_support_bill »

What is powering the Arduino?
Those capacitor leads don't appear to be soldered. And it is not clear what they are connected to.
What about the connections to the strip? We can't see those in the photo.
The 330 ohm resistor needs to be at the neopixel end of the signal wire to be effective. Ideally, one leg should be soldered directly to the strip.
If the strip is broken, why would it go from broken to working and back again?
You had intermittent connections to the strip. That can cause the strip to intermittently work or not work. It can also cause damage to the strip.

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squeakyneb
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

The Arduino is powered by either USB or a USB to 2.1mm plug cable (from Adafruit). Either way seems to make no difference.

The capacitor leads are indeed soldered. I've attached a closer photo. I can see how it might look unsoldered.

I don't see how it would matter which end of the line the resistor is in. It's between the Arduino and the signal input. It's just a resistor.

As for "broken and back again" because of intermittent connections, I really doubt that caused the problem. The problem started when I first connected the Adafruit powersupply and it's been a very consistent problem except for the 5 minutes when it inexplicably worked. I connect ground, I connect data, I connect positive, the strip flashes and then stays off. It does not sometimes work, it does not turn on and off repeatedly, the whole strip gives one flash and stays off no matter how long it's connected. It's not just fuzzing out because of a bad connection or working if I hold things right. If it has data, it'll flash once and turn off, very consistently.

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squeakyneb
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

Whoops, photo.
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adafruit_support_bill
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by adafruit_support_bill »

I don't see how it would matter which end of the line the resistor is in. It's between the Arduino and the signal input. It's just a resistor.
It is a line termination resistor and it is only effective in that capacity if it as at the end of the line. http://en.wikipedia.org/wiki/Electrical_termination
As for "broken and back again" because of intermittent connections, I really doubt that caused the problem.
At one point, you had an intermittent connection:
I had to resolder a power wire that I was holding in place
Operating it in this state can indeed cause damage.

Most often, the damage is limited to the first pixel. If you keep the power securely connected and move the data line to the DIN of the second pixel, the rest of the strip may still be operational.

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squeakyneb
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

It's not a line termination resistor. It's not a line termination at all. Line termination is to absorb signals on a disconnected line. Line termination is to prevent electrical resonance, and a Neopixel signal resonates at several hundred metres and my signal line is quite a bit shorter than that. This is a resistor, apparently intended to reduce spikes without damping out the signal. At any rate, closer examination shows a surface-mount resistor on the strip before the first pixel. It's a 2 metre strip, which I believe is a "full strip".

If you re-read my first post, that "intermittent connection" was when it WORKED. I turned it all off, soldered everything back in place, plugged the strip in again and it was back to broken (and I might point out that it's the exact same broken as before that).

I've tried skipping the first pixel. It's a commonly suggested fix and it changes nothing.

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squeakyneb
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

Oh, I missed your earlier question about how the power lines were connected: where the capacitor is, I either screwed into a screwblock power adactor or soldered to some short wires connected to my adjustable power supply.

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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

I just dug my multimeter out and your 5V power supply is pushing a steady 5.33. Would that be enough to kill it?

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Re: Neopixel strip flashes on for a moment then stays off

Post by adafruit_support_bill »

It's not a line termination resistor. It's not a line termination at all. Line termination is to absorb signals on a disconnected line
Not really. It is to match impedance with the input of the WS2812B.
If you re-read my first post, that "intermittent connection" was when it WORKED.
Yes, I read that. The last time it was working you were powering it via an intermittent connection.
I just dug my multimeter out and your 5V power supply is pushing a steady 5.33. Would that be enough to kill it?
They do not like much over 5.3v. Which power supply are you using to power the strip?

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squeakyneb
 
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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

Adafruit's 5V 10A supply, as per my first post.

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Re: Neopixel strip flashes on for a moment then stays off

Post by adafruit_support_bill »

What does your meter read when you measure the between GND and +5v on the Arduino?

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Re: Neopixel strip flashes on for a moment then stays off

Post by squeakyneb »

5.28 volts

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Re: Neopixel strip flashes on for a moment then stays off

Post by adafruit_support_bill »

5.28 volts
Sounds like your meter is reading high. This is not unusual when the batteries start to fade. Try the measurements again with fresh batteries in the meter.

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