Adafruit_ADXL375 VS Adafruit_NeoPixel

That doesn't say much. Are you using https://github.com/adafruit/Adafruit_ADXL375?

// Support for Adafruit NeoPixel LED driver #define NEOPIXEL_LED #if ENABLED(NEOPIXEL_LED) #define NEOPIXEL_TYPE NEO_GRB // NEO_GRBW, NEO_RGBW, NEO_GRB, NEO_RBG, etc. // See https://github.com/adafruit/Adafruit_NeoPixel/blob/master/Adafruit_NeoPixel.h //#define NEOPIXEL_PIN 4 // LED driving pin //#define NEOPIXEL2_TYPE NEOPIXEL_TYPE //#define NEOPIXEL2_PIN 5 #define NEOPIXEL_PIXELS 2 // Number of LEDs in the strip. (Longest strip when NEOPIXEL2_SEPARATE is disabled.) //#define NEOPIXEL_IS_SEQUENTIAL // Sequential display for temperature change - LED by LED. Disable to change all LEDs at once. #define NEOPIXEL_BRIGHTNESS 255 // Initial brightness (0-255) #define NEOPIXEL_STARTUP_TEST // Cycle through colors at startup // Support for second Adafruit NeoPixel LED driver controlled with M150 S1 ... //#define NEOPIXEL2_SEPARATE #if ENABLED(NEOPIXEL2_SEPARATE) #define NEOPIXEL2_PIXELS 15 // Number of LEDs in the second strip #define NEOPIXEL2_BRIGHTNESS 127 // Initial brightness (0-255) #define NEOPIXEL2_STARTUP_TEST // Cycle through colors at startup #define NEOPIXEL_M150_DEFAULT -1 // Default strip for M150 without 'S'. Use -1 to set all by default. #else //#define NEOPIXEL2_INSERIES // Default behavior is NeoPixel 2 in parallel #endif // Use some of the NeoPixel LEDs for static (background) lighting //#define NEOPIXEL_BKGD_INDEX_FIRST 0 // Index of the first background LED //#define NEOPIXEL_BKGD_INDEX_LAST 5 // Index of the last background LED //#define NEOPIXEL_BKGD_COLOR { 255, 255, 255, 0 } // R, G, B, W //#define NEOPIXEL_BKGD_ALWAYS_ON // Keep the backlight on when other NeoPixels are off #endif

neopixel code is the strandtest: https://github.com/adafruit/Adafruit_NeoPixel/blob/master/examples/strandtest/strandtest.ino

Lookup NeoPixel library

adafruit/Adafruit_NeoPixel has assembly code for AVR. Plus ESP and Rpi which are a lot easier to read. And the protocol does look like inverted WS2812; it should be possible, although tedious, to modify the library to invert the pin.

I looked at the neopixel github and I couldn't find any functions that took floats as arguments, so I think you can get away without using floats because they're reinterpreted as ints and truncated anyway, but if what you have works then don't bother.

I'm not sure if that is the same thing. Back when I used it I got it from Adafruit which links to this Github.

The most important question first, the Adafruit NeoPixel Library does support the RP2040 since version 1.10.2. So make sure you are using the right version. To install the library please follow the steps explained here: Adafruit NeoPixel Installation.

The Adafruit Neopixel library is great, but uses 3 bytes of RAM per pixel....in my application that's nearly 3kB (for the pixels alone!), which rules out the M328/Uno, and basically all of the 8-bit chips. I have a prototype running well using Adafruit's Neopixel library on a Mega 2560, but those are hard to source in the current market. And it's overkill for my use case.

Using something like the Adafruit NeoPixel library there are commands to set intensity and to set color: setBrightness() setPixelColor()