This project lets you dress up a window, Halloween prop or wall decoration with eye-catching LEDs that simulate dripping liquid, but leave no mess behind…it’s a completely dry effect!

Also, just changing the color and the prop, this is perfectly usable for Christmas decor as well. This is one of those “sandbox projects” that can fit wherever your imagination takes it…I’m just really partial to Halloween, so that’s what’s demonstrated here. Raawr!

The idea for this stemmed from three things

First: the arrival of some crazy skinny NeoPixel strips…just 4mm wide! From any reasonable viewing distance they almost disappear. As explained on the next page, bigger projects may do just fine with regular-size NeoPixel strip, easier to work with.

Second: our NeoPXL8 FeatherWing (distinct versions for M0 or M4 Feathers) is designed to run up to 8 NeoPixel strips concurrently. Most folks focus on the speed of this, but I’d been looking for a project to showcase the topological benefit…that each strand doesn’t need a return line to the next. We use this to make “drips” that end in mid-air.

Third: I’m a sucker for any project using age-old theatrical tricks with new technology…the simplest thing is suddenly indistinguishable from magic

Each of our “drips” briefly makes a “splat” where it lands…but there’s an air gap there, not a contiguous strip of NeoPixels from top to ground. It’s like a one-pixel version of a film editor’s cutting on action: hero throws knife, cut to villain with knife in his chest. Timed just right, we see a continuous motion out of two separate shots. Similarly, our dot jumps from A to B just when you’d expect, and the brain fills in the story. Brains are hilarious.

Things You’ll Need

Read through the whole guide before making any purchases…it’s full of tips and alternatives, and your build will probably end up slightly different. But in general you’ll need these items:

  • Feather M0 Basic Proto or Feather M4 Express and headers. The M0 has sufficient “oomph” for the project…but if you have a Feather M4 already, or want a more capable board to re-use in other projects later, that works also. This project can work with other “M0” (SAMD21) and “M4” (SAMD51) boards such as the Adalogger…but you may need to change some jumpers on the NeoPXL8 FeatherWing. We’re not using any special features here so it’s cheapest and easiest just to go with the Basic Proto. The project uses SAMD-specific features and will not work with other microcontrollers like AVR or ESP8266.
  • NeoPXL8 FeatherWing. There are two distinct versions: one for M0 Feathers, one for M4. The two are not interchangeable. There’s also a breakout version if you’re using something like an Adafruit Metro or Arduino Zero. But for the Feather M0 or M4, easiest to use the FeatherWing.
  • NeoPixel strips and pixels (explained further in guide)
  • Lots of wire
  • Soldering iron and related paraphernalia
  • Sundry craft supplies and tools; this will vary with how you decide to implement the project. There will almost certainly be hot glue involved…but I also found myself using masking tape, a permanent marker, hobby knife, foam core board and acrylic paint.

This guide was first published on Oct 23, 2019. It was last updated on Oct 23, 2019.

This page (Overview) was last updated on Jun 11, 2022.

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