Powering Neopixels from 3.3V boards?

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raysblog
 
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Powering Neopixels from 3.3V boards?

Post by raysblog »

Been reading about microcontrollers and Neopixels and there's something I don't quite understand.

Lots of microcontroller boards have 3.3v logic and power, like this one:
https://www.adafruit.com/product/3857

When I look around at the Neopixels, they seem to mostly require 5v logic/power. For example:
https://www.adafruit.com/product/1487

Now, when I look around at guides for Neopixels, I see some that are directly powering the 5v Neopixels from the 3.3v microcontrollers. For example:
https://learn.adafruit.com/sqaure-neopi ... ed-acrylic

However, further reading leads me to this nice writeup of how you're supposed to shift logic levels using a logic level converter:
https://learn.adafruit.com/neopixel-levelshifter

So -- what am I missing? Is logic level shifting not completely required? Does the shift just give you extra brightness or stability? Are these writeups directly connecting 3.3v microcontrollers to 5v Neopixels just bad practice? Or am I just not understanding some key part of all this?

Thanks!

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Re: Powering Neopixels from 3.3V boards?

Post by adafruit_support_bill »

Although rated for 5v, we have found that the pixels work reliably as low as 3.7v. There are some constraints:

The voltage for the pixel control signal to the pixels should be close to the pixel supply voltage (at least 75%) for reliable operation.

However, the control signal voltage MUST NOT exceed the supply voltage to the pixels.

So, with a 3.3v processor and 5v pixels, you will need a level shifter for reliable operation.

However, if you power both the processor and the pixels from a 3.7v LiPo, things will work just fine. If you check out the guides in the Learning system, you will find many projects designed that way.

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Re: Powering Neopixels from 3.3V boards?

Post by raysblog »

Thanks - this part I don't get:
adafruit_support_bill wrote: Sat Aug 13, 2022 4:52 pm So, with a 3.3v processor and 5v pixels, you will need a level shifter for reliable operation.
So when I read guides that are powering a 3.3v microcontroller through USB, and powering Neopixels -- that's not the way to do it? Wouldn't that be unreliable?

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Re: Powering Neopixels from 3.3V boards?

Post by adafruit_support_bill »

Please provide a link to the guide you are referring to.

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Re: Powering Neopixels from 3.3V boards?

Post by raysblog »

Take the original guide I referenced as an example [1].

On the circuit diagram page [2], you have this statement:

"The Adafruit board can be powered via USB or JST using a 3.7v lipo battery. In this project, a 1200mAh lipo battery is used.'

So, granted, they used a 3.7 lipo battery here, but the statement about the alternative power choice of USB is really what confused me. You couldn't just use the USB here instead of the lipo. You would need to also use the logic leveler if you decided to follow this guide but to use USB instead, correct?


[1] https://learn.adafruit.com/sqaure-neopi ... ed-acrylic
[2] https://learn.adafruit.com/sqaure-neopi ... it-diagram

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Re: Powering Neopixels from 3.3V boards?

Post by adafruit_support_bill »

If you look closer at the circuit diagram for that guide you will see that the pixels are powered from the (regulated) 3.3v pin of the Feather. They are not powered direct from the 5v USB.

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Re: Powering Neopixels from 3.3V boards?

Post by raysblog »

Right. But if the board itself was powered via USB, you would need a logic leveler between the Feather 3.3v pin and the Neopixels - is that right?

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Re: Powering Neopixels from 3.3V boards?

Post by adafruit_support_bill »

All Feathers operate at a 3.3v logic level. They have an on-board 3.3v regulator that will handle either 3.7v from a LiPo or 5v from USB as a supply voltage.

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