Neopixel work without power (!?!)

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julienz
 
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Neopixel work without power (!?!)

Post by julienz »

Hi there,
I stumbled across something odd to me:
I'm using an arduino uno and a motorshield (adafruit # 1438) and I'm trying to have two chained neopixel sticks (adafruit #1426) to light up with the idea of making a bargraph.
To test the examples of the libraries I wired the neopixels to the USB powered arduino using pin 6, Gnd and Vin (yes, I know, I only realized that later on...). From what I gather that made the current flow in reverse in through the arduino power regulator (5V pin and USB being linked and a load on Vin: one of the 15 ways to toast an arduino). Yet everything worked well, the pixels were very bright and all and the arduino is still up and running.
Then, as I wanted to move forward with my project I stacked the motor shield, powered the neopixels from the shield and wired the data line to pin 11. Based on the "Powering Neopixel" page I inserted a 470 Ohm resistor just before the first pixel on the data line.
At that point, the arduino is still fine but I can no longer get any of the pixel to light up. It looks like something happened not to the arduinbo but to the Neopixels as they seem to derive their power from the data line while the +5V power line is irrelevant, they will only light up (and change color etc) if I don't insert the 470 Ohm resistor on the data line and then will light up even if the power line is disconnected...

So what should my next move be ? I am tempted to proceed with the sticks as they are, without the resistor on the data line but the whole behaviour looks odd to me and I'm worried they might not last. If I am to replace the sticks because the drivers got screwed up at some point, I'd rather do it know than once the project has been completed and everything is nicely settled in a box.
Thanks for your input !!


Julien

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adafruit_support_rick
 
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Re: Neopixel work without power (!?!)

Post by adafruit_support_rick »

Powering the neopixels from Vin while hooked up to USB power is not a problem. It's actually recommended, if you've only got a few pixels and you're not powering them separately.

I'm not quite picturing the situation with the motor shield. Are you using an external power supply with the motor shield? Is that where you're getting the NeoPixel power from or are you still getting it from Vin?

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julienz
 
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Re: Neopixel work without power (!?!)

Post by julienz »

Hi Rick,
I am not sure about it being cool to put a load on Vin while powering it through the USB (looks a lot like method #8 to me) but I'll take your word for it.
To answer your question, right now the motorshield is stacked on the arduino for later use, so I connect the neopixel through it on pin 11 for the data line and on the +5V and Gnd pins. But that does not change anything so lets simplify the question and forget about the motorshield.
Upon further tests (tried without the motor shield and with a different arduino) I can tell something is definitely wrong with the Neopixels.
First the "simple" example coming with the library don't work anymore (no matter what arduino uno board). At most I get a faint red glow on some pixels IF I set the delay to 10. I have only one sketch that actually get them to light up significantly (it doesn't initialize the pixels and has a delay of 10) and even then the second pixel on the line shows some red flickering that shouldn't be there.

Code: Select all

#include <Adafruit_NeoPixel.h>

#define NeoPixel_PIN   11
#define NUMPIXELS      16
Adafruit_NeoPixel pixels = Adafruit_NeoPixel(NUMPIXELS, NeoPixel_PIN, NEO_GRB + NEO_KHZ800);


void setup() {
  pixels.begin(); // This initializes the NeoPixel library.
}

void loop() {
    
  unsigned int rgbColour[3];

  rgbColour[0] = 0;
  rgbColour[1] = 128;
  rgbColour[2] = 0;  

  for(int b=0; b<255;b++)
  {
    pixels.setBrightness(b);  
    for(int i=0; i<NUMPIXELS; i++){ 
      pixels.setPixelColor(i, pixels.Color(rgbColour[0],rgbColour[1],rgbColour[2]));
    pixels.show();
   }
   delay(10);
  }
  
}
With that sketch, "powering" the Neopixels from Vin and Gnd here is what I get :
The neopixels sticks connected on pin 11, Vin and Gnd only
The neopixels sticks connected on pin 11, Vin and Gnd only
IMG_2370.jpg (56.52 KiB) Viewed 290 times
Now, if I power the neopixels from 5V and Gnd on the board I get exactly the same thing because ... I get it anyway, even if the power 4-7Vdc is not connected !:
The &quot;unpowered&quot; neopixels sticks connected on pin 11 and Gnd only
The "unpowered" neopixels sticks connected on pin 11 and Gnd only
IMG_2372.jpg (53.41 KiB) Viewed 290 times
So I guess something went bad for the neopixels at some point, be it a careless connection-deconnection that I am not aware of or putting a load on the Vin of the USB powered arduino uno (my macBook did warn me that a USB device was consumming a lot of power back when the neopixel were shinning very brightly but not anymore) and now they got in this weird state where they look to me like they are drawing theire power from the data line so with the associated power limitation that makes them look dim or even unresponsive...
So, unless you have a another idea of test, I'll try to power them directly from a separate 5V source (being carefull to also add a 1000µF-16V capacitor), test each neopixel stick independently and if nothing brings them back from the weird place they are at, I'll just replace those (and keep them as the weird ones...).

Thanks for your answer !!

Julien

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adafruit_support_rick
 
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Re: Neopixel work without power (!?!)

Post by adafruit_support_rick »

Method #8 is different - that involves applying power to the 5V output pin. It's different if you apply power through USB.

You must have burned out a pixel when you got that overload warning. Otherwise, there's no way they would light up with just data and ground connected.

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julienz
 
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Re: Neopixel work without power (!?!)

Post by julienz »

So, I got back to the little neopixel sticks, and tried a seperat power supply (with the recommended capacitor), under 6V two neopixel sticks (16 diodes) only drew 60 mA. I seperated the sticks and tested them separatly : the first one (the one getting the data line in and the power) does not work at all on its own, the second one works like a charm and is as bright as can be.
So the first stick looks dead, unless I can by-pass the first diode and still use the 7 behind?

Thanks for your answers anyway, I'll just order a handfull of those sticks just to be sure.

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Re: Neopixel work without power (!?!)

Post by adafruit_support_rick »

Please email [email protected] with a link to this thread for a replacement neopixel stick

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