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Gemma M0 - Chain Additional NeoPixels from Onboard Neopixel?
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Gemma M0 - Chain Additional NeoPixels from Onboard Neopixel?

by lostchocolatelab on Wed Apr 07, 2021 12:35 am

Using the Gemma M0, Is it possible to "chain" additional Neopixels from the Onboard Neopixel?
(any way to "jumper off" the Gemma M0 PCB to string additional neopixels and "duplicate" the behavior of the on-board neopixel?)

I've monopoloized all of my control ports with analog potentiometers to drive parameterization, but would love to add some additional Neopixels to the on-board neopixel behavior.

Thanks in-advance for lending some perspective!

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Re: Gemma M0 - Chain Additional NeoPixels from Onboard Neopi

by adafruit_support_mike on Wed Apr 07, 2021 1:11 am

The RGB LED on a Gemma M0 is a DotStar, so you can't chain it to NeoPixels at all. Not only are the protocols different, they use a different number of signals.

It's technically possible to connect wire jumpers from the DotStar to an external strip, but it would be difficult.. I'd hesitate to do it, and I'm comfortable building freeform circuits with SMT parts.

It would be easier to tack a piece of 30-gauge wire to one of the microcontroller's pins, then secure the wire to the top of the chip with a dot of hot-melt glue. Then you could use that pin to control a strip of NeoPixels.

The Gemma M0's Variant.cpp file defines four GPIO pins that aren't broken out on the board, but are required (for some reason) by the rest of the Arduino code. The physical pins are on the corner diagonally across from the notch:

gemma-pins.png
gemma-pins.png (127.19 KiB) Viewed 58 times

In code, the numbers will be:

Code: Select all | TOGGLE FULL SIZE
PA14 -> 17
PA15 -> 18
PA16 -> 19
PA17 -> 20

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Re: Gemma M0 - Chain Additional NeoPixels from Onboard Neopi

by lostchocolatelab on Sun Apr 11, 2021 4:06 pm

This is incredibly inspiring, thank you for taking the time to detail this possibility. Great to hear that it's possible, I'll see if I can manage the 30 gauge wiring!
I also appreciate the terminology correction re: DotStar...no matter how many articles I've read, I still couldn't quite get it straight! X)

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