A digital, 3D printed sundial whose precise holes cast a shadow displaying the current time

Julldozer created an amazingly clever digital sundial ("Cadran Solaire Numérique") that precomputes the angle of the sun throughout the day and uses those computations to make hundreds of precise holes calibrated to cast a shadow displaying the present time.

The whole thing is open source hardware, with 3D files on Thingiverse; but if you want to buy a premade one, Mojotpix will sell you one for $80.

No batteries, no motor, no electronics... It's all just a really super-fancy shadow show. The shape of the sundial has been mathematically designed to only let through the right sunrays at the right time/angle. This allows to display the actual time with sunlit digits inside the sundial's shadow.

The sundial displays time (with actual digits !!) from 10:00 until 16:00, updating every 20 minutes. You can precisely adjust the displayed time simply by rotating the gnomon (the magic box that displays time). So you can even adjust for Daylight Saving Time.

Digital Sundial [Mojoptix/Etsy]

ep. #001: Cadran Solaire Numérique [Julldozer/Mojoptix

(via JWZ)

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  1. SamSam says:

    I don't think it ought to matter, if the holes are designed right. In simplistic terms, the "vertical" angle will change throughout the year, but the "horizontal" angle won't. So long as those numeral holes aren't round holes, but are more like slots, then this should work even with a changing vertical angle. Much like a sundial's shadow will still hit the hour lines, even though the shadow itself becomes longer and shorter.

    More precisely, the hour lines aren't straight lines but make an analemma, but I don't know whether this is significant enough in a small sundial that it needs to be factored in to the shape of the holes, or if the holes can just be a little bigger to allow for some wiggle room.

    If it's precise enough, it could actually be more accurate than a regular sundial, because if the pin holes can account for the analemma then that takes care of the Equation of time inaccuracy. But thinking about it, maybe we can't account for that just in the hole's shape, and that needs to involve marking the locations of the numbers on the base.

    Without fancy adjustment, it's still fairly accurate throughout the year, just as a regular sun dial is.

  2. PRANK IDEA: Find someone who has one of these and replace it with an identical-looking version that just flashes "12:00" all day. Then tell them that they have to reset the time due to a recent solar eclipse.

  3. SamSam says:

    PRANK IDEA: Replace the Earth with one that doesn't spin. Then all the sundials will be stopped. Tell people that they have to unplug the Earth and plug it back in again. When it doesn't work, tell them that they didn't wait the full 60 seconds.

  4. Hunting for an on-line copy of Ian Stewart's article on digital sundials (Sci.Am., 1991) led me to the Whackyweedia article


    which in turn links to a number of instantiations of the concept.

  5. You're the owner of that Etsy shop (3Dexpression)... so you ordered a Digital Sundial from yourself (??). I guess it's good that you received it only 4 days later.
    (Just following the breadcrumbs: waternut131434 .... https://twitter.com/waternut13134 .... https://www.instagram.com/3dexpressions/ )

    Anyhow, I am just teasing you :wink: I really don't mind, quite the opposite even: I think it's pretty cool that you're 3D printing and selling my design !! Keep it up !
    ( maybe please just mention somewhere on your page my name and website )

    I open-sourced all the 3D files for my Digital Sundial on Thingiverse under a CC-Attribution licence (instead of a non-commercial CC-SA or CC-NC licence, which is more typical on Thingiverse) specifically for that purpose : so that other makers could make some pocket money with it, if they ever wanted to. It is one of the most permissive licence: you can not only print your own digital sundial, but also modify it, and even sell it. The only thing you "have to do" is mention the author ( me ! ).
    The underlying idea is that "Makers" (people that can make things) can potentially make unique things that "Geeks" (people that like cool stuff) might be interested in buying (such as a Digital Sundial).

    Julldozer (from Mojoptix)

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