You could certainly be forgiven for thinking that the term "digital sundial" is simply an example of an oxymoron, not unlike "jumbo shrimp" or "deafening silence." That hasn't stopped French Thingiverse member Mojoptix from building one, however. It contains no electronics or moving parts, yet it still shows the time from 10:00 to 16:00 in a changing numerical display – with a little help from the sun.
First of all, there are indeed other digital sundials, although they generally don't have the traditional shadow-casting sundial form factor. Instead, they utilize optical fibers or layered masks, and are viewed face-on like a clock.
By contrast, Mojoptix's creation has the usual angled pointy bit in the middle (known as a gnomon), the shadow of which moves around in a circular path as the sun traverses the sky. Instead of pointing to numbers on the ground, however, that shadow displays the time in 20-minute increments within itself as it moves.
Mojoptix designed the sundial using free OpenSCAD software, then took about 35 hours to build it out of ABS plastic on his Ultimaker 2 3D printer.
The finished product is full of tiny slots, which go through it at a variety of angles. Depending on the angle at which the sun is hitting the top of the device, the sunlight will pass through some of those slots, each one showing up as a pixel of light in the shadow. Depending on the combination of slots that are lined up with the sun at any one time, the pixels will combine to make up a different time display.
To set the sundial up, users first stick it on a weighted glass jar (that they provide) via a built-in screw mount on the bottom. They then make sure that the device is facing north if they're in the Northern Hemisphere, or south if they're in the South. From there, they adjust the angle of the gnomon to compensate for the latitude at which they're located, along with the current season. If the time is still a little bit off, it can be tweaked by twisting the gnomon to one side or the other – this also lets them adjust for daylight saving time.
Mojoptix is supplying open-source instructions to DIY-ers who wish to make their own digital sundials from scratch, although he'll also sell you a kit consisting of pre-printed components that you just put together. It's available on his Etsy store, for about US$77.
For a more detailed account of its creation, check out the video below.