I picked up this plastic dragon skull candy dish among the seasonal merchandise at a local big-box store. Mostly because I like dragons. But also…tell you a secret…I wasn’t certain this idea would work. The dragon skull was a good size for a Monster M4sk eyes project as a Plan B!
In hindsight, I’d recommend aiming bigger. Lots of stores have hanging ghouls, werewolf skeletons, elaborate foam tombstones and so forth, any of which would look fantastic with some ooze!
Reason I suggest this is because big props are more to-scale with classic NeoPixel strip, which is easier to work with. The ultra-skinny strip is amazing but requires patience and top-level soldering skill.
I already had the dragon skull though, so that’s what I’ll walk through here…
Photo credit: Target
Oozes and Dribbles and Drips, Oh My!
The ooze (or blood, or water) animation along each NeoPixel strip follows a certain sequence…
- An initial “oozing” from a single point…like a tear will well up in your eye before falling.
- A slow “dribbling” part way down the strip…think of the tear now trickling down your face to your chin.
- “Dripping,” falling from chin to ground.
- A “splat” where it hits the ground.
These distances are all configurable in the software on a per-strip basis. The way that everything oozes, dribbles and drips along different lengths gives it a more natural (or supernatural?) appearance.
The dribble portion requires a contiguous length of NeoPixel strip. The drip only needs to cover about half the distance to the splat…it just ends in empty air, and the single ground splat NeoPixel completes the illusion.
Look over your Halloween prop and decide where your dribbles and drips will go, and measure distances to figure how many NeoPixels you’ll need. Remember that you’ll need to span the full distance of a dribble, and about half the distance of a drip.
NeoPixel strips come in specific densities and lengths. If your total works out to just a few pixels over such a threshold, it’s OK to shorten some drips by a pixel or two…the illusion still works.
I found that this dragon had a slight underbite, and drips from the nose would have landed on the lower teeth. While that’s possible and would look cool, I wanted to keep it simple with all the drips on the table. Scrounging in the garage for any piece of junk, I found this spray can cap and hot-glued it at the rear base of the skull to tip it forward a bit, problem solved.
Splat positions and numbers (0 to 6, corresponding to each drip) are marked on the base…these distances are needed later.
Base was a piece of foam core board, but just about anything the right size would work…a piece of wood, cardboard box flap, or a plastic serving tray.
The code and hardware for the OOZE MASTER 3000 can animate up to 7 “drips,” with an 8th wire driving the “splats” on the ground. Here’s a schematic view showing the NeoPXL8 FeatherWing and NeoPixel strips:
THINGS TO KNOW:
- This is a schematic diagram, not a literal wiring diagram. Look closely at your NeoPixel strips, they often have input pads in a different order.
- You can have fewer than 7 drips if you want, but always start from NeoPXL8 output #0. The splats are always on NeoPXL8 output #7.
- Your drips will probably a mix of lengths!
- The Feather RP2040 SCORPIO board came along later, but the principle is exactly the same…connections are simply at one end of the board rather than down the middle.
Q: What if I want more than 7 drips?
A: Some options…
-
You can drive 8 drips from one board, but you won’t get ground splats in that case.
-
You can just build multiple units. There’s nothing that needs to be synchronized between them.
-
It’s possible to split the output signals if you’re OK with duplicate identical drips in places…this is discussed on the last page.
For the “splat” NeoPixels, where each drip hits the ground, I used several of these “Mini Button PCB NeoPixels,” one per drip — but there are lots of other options, depending on soldering skill and available resources…
Flora RGB Smart Pixels and Breadboard-friendly RGB Smart NeoPixels can also be individually soldered into a chain. Or, if the pixel spacing works for your project, this NeoPixel LED Strand might avoid a lot of intricate soldering.
If you’ve done projects with NeoPixel strip previously, or if that’s what you’re using for your “drips,” odds are you have a few strip end-trimmings that you’ve held onto. These can be cut to individual pixel strandlets and then solder wires between them.
Power
I decided to power my dragon from the Feather board’s USB port, plugged into either a USB charger or power bank. This just made everything a lot easier…using a bare LiPo battery would require a couple extra components and expense, but everyone has a spare charger and USB cable.
To distribute power to all the LED strands, I sawed some of the power rails off a Perma Proto PCB, and soldered this to the NeoPXL8 FeatherWing’s USB (5V) and GND pins with 22 gauge wire.
There’s other ways this could be done, but being able to “home run” all of the power to this one spot made things easier to keep track of.
Wire
You are going to need SO. MUCH. WIRE. Even just this little dragon centerpiece, about 13 inches long, used about 30 feet of wire, divided evenly between red, black and green (to better keep track of 5V, ground and data wires).
For the dragon, I used 26 gauge stranded wire throughout (except for the two thicker wires to the power distribution rails). Even 28 gauge would suffice, as it’s a tiny project. For something bigger…more pixels or longer distances…consider using heavier gauge wire for power and ground, but keep the data wires thin.
If your project is something like the hanging ghoul (or simply dressing up a window frame), with some distance between the “drips” above and “splats” below, it should be fine running wires a few feet to the splat NeoPixels. There’s no defined hard limit I can provide, sometimes you just have to build and adapt…I’d feel confident running wires 4 or 5 feet, but 10 feet or more just seems iffy for the signal to get through reliably.
