That’s like a sundial, but with better resolution– not just an hour hand, but a minute and second hand as well, each given as a shadow from moving artificial light sources (bulbs).
We’ve recently put together a working bulbdial clock, with an implementation somewhat different from that of the original concept.
Rather than using three physically moving light sources at different heights, we use three rings of LEDs at different heights. Within each ring, we only turn on one LED at a time, so that we only have a single effective light source– it can light up at different places from within the ring. The three rings are located above one another so that they each project light onto the rod in the middle, making shadows of different lengths.
Additionally, for fun and clarity, we used red, green, and blue LEDs for the three rings, making each shadow hand of the clock a different color. Each ring has 12 LEDs, and the 36 LEDs are efficiently multiplexed by an AVR microcontroller that also handles the timekeeping part of the project. Continue reading A Bulbdial Clock