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 incredibly 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 and NeoPXL8 Friend boards are 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. Additionally, skim the NeoPXL8 guide for the latest on compatible hardware…several M0, M4, RP2040 and ESP32-S3 Feather boards can now work with this, though each may require some tweaks. But in general you’ll need these items:

  • A NeoPXL8-compatible development board such as the Feather M0 Basic Proto, Feather M4 Express, Feather RP2040 or Feather ESP32-S3, and some headers. Some non-Feather boards can work as well, but connections are usually simpler with this form-factor. Please see the NeoPXL8 guide mentioned above.
  • NeoPXL8 FeatherWing or NeoPXL8 Friend. There are two distinct versions of the FeatherWing: one intended for M0 Feathers, one for M4The two are generally not interchangeable, with an exception for the easy-going Feather ESP32-S3 that can use either. The “Friend” is a breakout version for non-Feather boards.
  • Or…the Feather RP2040 SCORPIO combines microcontroller and NeoPXL8 into a single board!
  • 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 May 27, 2024.

This page (Overview) was last updated on Mar 08, 2024.

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