Time taken: 20 hours
Materials: manuka pole from garden centre (170cm long), sheep skull, 12 gauge mild steel wire, 2 table tennis balls, acrylic resin, red pigment, stiff tulle, expanding foam, air-dry modelling clay, acrylic paints, finishing varnish, ATTiny85, hall effect sensor, hookup wire, switch, 9v battery and connector, 9v to 5v regulator, 2x superbright red 5mm LEDs, rare earth magnet, silver ring blank, fimo, leather strips, wool, hot glue.
Tools: Pliers, craft knife, soldering iron, hot glue gun, paintbrushes, laptop, modelling tools, scissors.
Techniques: Modelling, spinning, fabrication, electronics, coding.
Difficulty level: The code and circuitry is pretty basic, and the modelling is straightforward. Putting it together and making it work was a bit fiddly, so I’m going to say medium/hard.
I started with a sheep skull. This one was bought from a guy who works with bones in his garage for $40 but I guess you could go find your own if you were keen. I also bought a stick from the local garden centre. I chose manuka because it’s hard and has a nice grain. It came with bark on so I had to peel it.
The first part was to create a base for the horns. To do this I made a couple of spirals using three strands of 12 gauge mild steel wire. They were each inserted into holes I drilled in the skull about where horns would go, then curved using a picture of a Bighorn sheep as reference.
After that I twisted some heavy tulle around the wire to give it more grip for the foam application. Then the messy bit – adding the expanding foam. Expanding foam is awesome in that it’s very lightweight and you can carve it to any shape, but it’s really sticky and messy, and I find it a bit wasteful. So I took this outside and used up most of a can. The stuff doesn’t really keep once you’ve opened it anyway, so I figured I might as well go for overkill. At this point Yorick ended up looking like an 80s hairdo:
After about 24 hours, the stuff is dry enough to carve. I used a craft knife an just removed bits until I had the basic horn shape, then used a smaller one to fine it down until I was happy with their thickness and curve.
After that, I needed to add the ridges to the horns. First I filled in the holes (an inherent problem with expanding foam) with Sculptamold, then I used air-dry modelling clay for the ridges. Somehow I ended up buying pink instead of white, but I guess any colour will do really. I guess I could have carved these shapes from the expanding foam too, but that was a bit beyond my skills for such fine work.
After the ridges were on, it was time to paint. First I added a layer of a darkish cream colour:
And then slowly added layers of darker and darker colours until I got to burnt umber. Each layer was painted on thinly, then the majority wiped away to leave deposits in the cracks and crevices. As the colours slowly built up, the cream was mostly covered and only the very high points and tips were left light, giving the effect of horns. Pic of that later. Meanwhile, that’s the basic staff, but what about the circuitry?
*insert a whole bunch of soldering here*
The basic idea was that I’d use a rare earth magnet hidden inside a ring, to trigger a hall effect sensor (detects magnetic fields). This would send a reading to a microcontroller, which would turn the reading from the sensor into a meaningful message for the LED ‘eyes’ – “Get brighter” when the magnet was near, or “Turn off” when the magnet was taken away. This all needed a power source. Here is a picture of the circuit I made:
As you can see, it’s a fairly simple circuit. My brother made the eyes for me as he was experimenting with acrylics at the time – they are table tennis balls filled with red-tinted acrylic resin, leaving a 5mm gap for the LEDs to slot in behind. Here is a picture with the eyes added, and the microcontroller in the circuit:
The observant among you will note that that’s an Arduino Uno and not an ATTiny85. This is because the original code for reading the sensor and directing the LEDs was written for an Arduino, because that’s what I had – and Arduinos are much easier to breadboard than Tinys. Here’s the original code (clicky to embiggen):
The base reading of 517 that you see in there will vary from sensor to sensor, so it’s a good idea to get the reading for your own sensor and change this number accordingly. Also, the sensor’s sensitivity may vary so the padding might need to be altered as well. We found that with this code, we could get the sensor to light the eyeballs when the magnet was about 20cm away, and when the magnet was removed they would slowly go out.
Then it was time to put it all together. The skull was wired onto the staff using 12 gauge mild steel wire, and I made a small leather pouch to hold the battery and gubbins:
Meanwhile, the code had been transferred onto the ATTiny85, which was included in the circuit and carefully pushed into a slightly-widened brain box hole in the back of the skull. The sensor was glued to the staff in the area where it’d be held, and the eyes were glued into their sockets with the wires running back to the battery area.
In that pic you can see the finished horns as well.
This is the part where we ran into a spot of bother. For some reason, the sensor was reading weirdly in that it didn’t always register that the magnet had been taken away, so the eyes would stay lit even with no magnet present. After pulling everything apart, I discovered that this effect could be repeated by wiggling the wires around the sensor itself:
This caused a whole bunch of head-scratching and resoldering, including removing the microcontroller from its brainbox and replacing it, and redoing the entire circuit. The issue was never completely resolved, but I suspect that induction may play a part in this. However, we got it responding well enough for what we were trying to do by making sure all the connections were solid and the Tiny was not too cramped.
All that remained after that was to add some cosmetic effects, including spinning slubby wool in white, brown and dark brown to form a mane that would cover up the gubbins, adding some leather strips to cover wiring, and giving it a claw:
And finally, taking a photo of the whole thing, for posterity and because the internet needs more LED skull staffs of Extreme Tackiness.
Ta da! I didn’t take any photos of the ring, but it was simply a rare earth magnet embedded into a shaped piece of oven-fired fimo, and glued onto a silver ring base with superglue. When she wears the ring, the staff responds to her presence by lighting up. It’s both tacky and creepy and it’s awesome.