Sapphire Lantern (part 1)
2019-08-15 by Arman Frasier
After reading The Way of Kings (Book One of the Stormlight Archive by Brandon Sanderson) I was really enchanted by the world of Roshar's monetary (and, as it turns out, magical) currency system of Spheres. As a currency, they function as you'd expect, with various denominations carrying different economic values; however, the clever part comes in to play when, as it turns out, the gems at the center of the glass also holds stormlight - the magical essence that powers the abilities of certain characters.
Each sphere is made up of a gemstone (typically cut) surrounded by a glass sphere, with one side of the sphere flattened to help it remain stable when sitting upon a table.
And geez, don't they sound really cool? I think I'll make one.
I knew from the start that I wanted the sphere to be able to be held in the hand, and to not require connecting (via wires) to an external power source to generate the light. This means I'd need to power the sphere using wireless power.
Wireless power transmission works on the basic (if your last name is Faraday) principle that an alternating magnetic field generates a current in nearby coils of wire. This is known as Electromagnetic Induction, and it's the basis for how not only wireless transmission works, but also power transformers, electric motors, and generators!
I like to break down large goals into smaller, easier to track (and accomplish) tasks. To create a remotely-powered glowing sphere of stormlight, I'll need to do the following:
- Create a magnetic coil + LED circuit
- Encase said circuit in a gemstone
- Encase said gemstone in a sphere
- Create a base to induce an alternating magnetic field
The last part might be tricky. How to actually power that sphere? Perhaps a glove with a magnets, so when you move your hands the sphere glows? Fortunately, The Way of Kings provides a particular item we can use to mask our generating station. Characters navigate dark spaces by placing a (often sapphire) sphere into a lantern to light their way. So we will create a lantern, and incorporate a driving coil into the base.
The Driving Coil
The driving coil - the small circuit board uses DC power to create a varying current to the coil, generating an alternating magnetic field; which can induce current into a paired coil.
This part was arguably the easiest - I procured a driving coil that could operate off of DC power from Adafruit; because the magnetic field needs to be changing with respect to time to induce a current on the other end we can't just wind a coil and shove DC current into it. While this would result in a "blip" of light on the sphere, we needed the field to alternate to continue powering the light. Now for the arguably harder part.
The LED Circuit
To create the LED and Coil component, I decided to once again leverage Adafruit's catalog and purchase Magnet Wire and some LED sequins from them.
Magnet wire is a special sort of copper wire which is enameled, so that when it lays upon itself there is no electrical connection. If there were, it would be extremely difficult to wind a coil, as anytime the wire touched itself it would short out the circuit, resulting in a very poor inductor.
The harvesting coil - the magnetic field will generate a current in the coil, making the LED glow. Ignore my shoddy soldering.
Winding the coil was done... poorly. I don't have any specific winding tools, so I ended up using some scotch tape and winding it around the top of an isopropyl alcohol bottle cap. It works, but it's not perfect.
Now that we have our LED circuit, we need to encase it in a gemstone. My plan for this is to use a two-part epoxy art resin, and color it blue with some acrylic paint. But first, I need to create a mold of a gemstone. I decided to go with a larger gemstone than described in the books - taking a little bit of
artistic Ingenieurs license - to make it easier to work with.
Michael's to the rescue! I bought a box of decorative gemstones that you might see in the bottom of a flower vase, and used them to make a mold of a gemstone. Once the mold sets, I mixed up some artist's resin (using a drop of blue acrylic paint to give it a blue hue), and set the coil in it.
After the resin set, the same process was repeated on the other side. Resulting in a complete gem with embedded LED and power coil.
Testing the Gem
The moment of truth.
It Works! The video gets a little washed out, but you can see how it is being powered by the coil, and the gem glows nice and bright when it is drawing enough current. The final part now is to set it into a clear sphere.
Setting into a sphere
This part should be the easiest, right? Using some spherical resin molds procured from the internet, we can set the gem in the middle of a resin cast.
The resin was too viscous for the mold to hold comfortably, so it poured out of the side. (Next time: Tape the mold together!) I managed to rig up a solution before it all spilled out, but not without getting resin all over my hands.
Pro Tip: Keep acetone on hand before you get resin all over your hands.
The final sphere (or, prototype)
Well, we've let the resin set: let's take a look at the sphere.
So... there are some problems. The Gem is far too large; and combined with the magnifying effect of the sphere, it's hard to tell it is in there at all. The device works, which is good, but the sphere is uneven (due to the incident with the resin). Additionally, there are some notable air pockets that were trapped inside during the whole fiasco.
Yikes! Well, I guess we can call this one a prototype. I will do better.
And, you know what they say: Journey before Destination! In part 2, we will make our gems smaller, our spheres more spherelike, and get started on creating the lantern itself!