First prototypes

A project log for Fiber Optic Constellation Stepping Stones

Optical fibers embedded in concrete stepping stones light up zodiac constellations

Steve PomeroySteve Pomeroy 07/08/2020 at 02:130 Comments
First light! The test pour worked and the fibers light!

The big dipper isn't one of the zodiac constellations, so we decided to use it for the test prototype. We ordered three sizes of cylindrical silicone cake pans which we will be using for casting the stones. We used the smallest—6"—and cut out a scrap of wood to use as a base to set it on. We put together the star pattern in Inkscape along with registration marks to line it up with the circle, printed it out, and used that to drill holes in the plywood.

With the holes drilled in the wood, we used long straight pins to punch small holes in the silicone pan aligned to the board. We then used these pins to help guide the fibers through the board and cake pan. To keep the fibers from falling into the concrete, we looped pairs of neighboring stars together (with a tail for the odd one).

For the fiberoptics, we used 1mm plastic fibers (pretty easily findable on AliExpress/Amazon for cheap, but I had some laying around). We bound the ends of the cables together using a 10mm ferrule and a hex ferrule crimper. This seemed to work great, though it does mean a maximum of around 7 fibers per crimped bundle. The light output from a single APA102/SK9822 LED is plenty to light up 7 fibers so they can be seen clearly at night. Turns out LEDs are bright.

We used Quikrete 5000 80lb which was fine, but not great. Its aggregate is too coarse for this and caused there to be some indents and bubbles. For the remaining stones we'll probably use something that uses sand as the aggregate instead of gravel and also something that sets a bit quicker.