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NeoPixel strip acting weird
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NeoPixel strip acting weird

by lemoncraft on Tue Nov 07, 2017 7:49 pm

Hi there!

I have recently acquired my first NeoPixel strip and I have followed this tutorial: https://learn.adafruit.com/adafruit-neo ... onnections

What is the weird thing? When I get my hands close to the end of the strip (no touching) or touch the capacitor, the pixels change color and start blinking randomly. Same thing happens if the strip is rolled.
Is that behaviour normal?

The parts involved:
NeoPixel RGBW Strip (60 pixels/meter)
Trinket M0 recently updated with CircuitPython 2.0
470 ohm Resistor
4700 uF 10v Capacitor
5v 2amp Power source

I am powering the Trinket using a USB cable connected to a PC and the strip get its power from the 2amp power source.

Things I have checked:
Common ground is connected to the Gnd pin of the Trinket and Gnd of the strip.
I have added bpp=4 to the NeoPixel constructor in my Python code.


The only thing I can think of is that my hands are offering a way to ground and that is messing with the signal.
I have also noticed that the more pixels that are turned on this weird behavior tends to disappear

Any help is welcome
Thanks in advance!

lemoncraft
 
Posts: 5
Joined: Sun Jul 10, 2016 3:49 pm

Re: NeoPixel strip acting weird

by adafruit_support_bill on Tue Nov 07, 2017 9:31 pm

With the strip powered by 5v, and controlled by a 3.3v processor like the M0, you usually need to have a level shifter on the signal line for stable operation.

https://learn.adafruit.com/adafruit-neo ... -following
NeoPixels powered by 5v require a 5V data signal. If using a 3.3V microcontroller you must use a logic level shifter such as a 74AHCT125 or 74HCT245.

adafruit_support_bill
 
Posts: 63022
Joined: Sat Feb 07, 2009 10:11 am

Re: NeoPixel strip acting weird

by lemoncraft on Wed Nov 08, 2017 6:18 pm

Yes! that was it.

I don't have any of those at hand, but I have connected the strip to the 3v output pin of the trinket and everything looks nice now.
Thanks a lot.

Another thing I've noticed; if I put the strip to full bright (1?) the speed increases a lot:

strip = neopixel.NeoPixel(pixpin, numpix, brightness=1, bpp=4, auto_write=False) # Faster
vs.
strip = neopixel.NeoPixel(pixpin, numpix, brightness=0.3, bpp=4, auto_write=False) # Slower

lemoncraft
 
Posts: 5
Joined: Sun Jul 10, 2016 3:49 pm

Re: NeoPixel strip acting weird

by adafruit_support_bill on Wed Nov 08, 2017 8:16 pm

I don't know of any reason why the voltage should affect the speed. But the 3v pin of the Trinket will not be able to power very many Neopixels reliably.

adafruit_support_bill
 
Posts: 63022
Joined: Sat Feb 07, 2009 10:11 am

Re: NeoPixel strip acting weird

by lemoncraft on Wed Nov 08, 2017 9:34 pm

I know.. but for testing purposes it will suffice.
Next time I will include a level shifter.

Thanks for your help

lemoncraft
 
Posts: 5
Joined: Sun Jul 10, 2016 3:49 pm

Please be positive and constructive with your questions and comments.