The episode in [ENGLISH]: http://www.mojoptix.com/2015/10/25/mojoptix-001-digital-sundial/
L'épisode en [FRANCAIS]: http://www.mojoptix.com/fr/2015/10/12/ep-001-cadran-solaire-numerique
A Sundial displaying the time inside its shadow, with actual digits ! There is a tiny bit of magic inside...
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.
You'll also need :
--- an (empty !) jam jar
--- 3x M6 screws, flat head, length = 20 mm
--- 1x M6 screw, flat head, length = 50 mm
--- 4x M6 nuts
--- 4x M6 washer, outside diameter < 14mm