First Pixel Dies

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

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adafruit_support_bill
 
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Re: First Pixel Dies

Post by adafruit_support_bill »

Can you give us some more detail about your system and how you are powering it? A photo would be good too.

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adafruit_support_mike
 
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Re: First Pixel Dies

Post by adafruit_support_mike »

Try putting a 10k resistor between the DIN and GND pins at the input end of the strip.

The 'dead first pixel' problem is something we still haven't completely figured out, but one theory (okay, mine) involves small amounts of induced current from mains wiring or flourescent lights nearby. Putting a 10k between the DIN and GND pins will give that kind of current a harmless path to ground.

I'm asking people to see if it does any good. If so, we might have an answer for this kind of problem. If not, we'll know that isn't it and can start looking at other possibilities.

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primosz
 
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Re: First Pixel Dies

Post by primosz »

Can somebody using that 10k Ohm resistor can confirm that it prevent from killing first LED?

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pburgess
 
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Re: First Pixel Dies

Post by pburgess »

Would you be willing to try some science for me?

Could you connect the power supply (with capacitor) to the far end of the strip? Keep DIN and GND connected to the Arduino (with resistors as you have), just move the power business to the other end (the strip doesn't care which end it receives power through).

If another pixel pops...is it still at the head end, or does it now manifest at the far end?

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adafruit_support_mike
 
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Re: First Pixel Dies

Post by adafruit_support_mike »

Another suggestion currently under testing is to put a 10k resistor between the DIN and GND pins at the point where the wiring connects to the NeoPixel strip.

I've done some work with high-impedance circuits, and know from experience that a wire with just a mosfet (or any other logic input) at the end can see 1v-2v of voltage from antenna effects. Most of it is at 60Hz, and the biggest offenders are mains wiring and flourescent lights. The induced current is on the 100 nanoamp level, but V=IR and when R=10M to 20M (typical for logic inputs), even that can produce some impressive voltage spikes.

If induced current *is* the problem, giving it a lower-resistance path to ground should reduce the induced voltage to a few millivolts.

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