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Guy Marsden
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David Bruckenstein
Light Guide Clock

August 2019

This is my third collaborative project with Dave Bruckenstein.  We call this one the Light Guide Clock due to the 1/2" acrylic rods inside that guide the light from LEDs in the back to the clock face.  The original premise was to create a sense of magic so that people would wonder how the light got to the face.  It turns out that the walls of the rods are more visible than we expected, but we like the result nonetheless.

Dave likes to do CAD visualizations as the design evolves and we explore options for materials and technology.  We started with a very basic rectangular wood base and it evolved as we worked out the cylindrical clock "mechanism" as a removable module.
Below is the final design - we later added a clear cylinder to keep the dust off the light guides.
In the image below right - the time displayed is 8:05.  The blue dot is the hour and the red one shows the minutes to the nearest 5, so it is not that accurate for any given minute.  What is neat is that when the hands overlap at say 1:05 there is just one dot that shows as purple since the colors combine.  This makes reading the time a little inscrutable which is an essential part of Dave's concept for his clocks.
Once we had settled on the dimensions I designed a circuit board with programmable RGB LEDs on the front and circuitry on the back.  This design incorporates a real time clock chip with battery backup so it can retain the correct time even if left unplugged for weeks.  There are 2 set buttons that allow you to adjust for daylight savings time. 
Once that was assembled, I had to program the light sequences and get the real time clock code working which took way longer than anticipated due to the weird number format used in the clock chip to represent time.  (For you geeks, it uses binary coded decimal). 

My next step was to construct the cylindrical assembly.  We both gave the dimensions of the black and white material a lot of thought.  So the front has 1/8" translucent white for the clock face, and that is backed by 1/4" black to support the light guides and to isolate the dots of light.  The back has a 1/2" thick piece of black that also supports the PCB and the light guides that are made of 1/2" diameter acrylic rods.  There are 3 magnets that align with 3 in the case so that the module indexes into the correct orientation and is held in place firmly.  You need to pull the module out to set the time.
Finally I acquired a nice piece of black walnut that I cut and glued up to get the thickness we wanted.  Then I turned it on my lathe. 
In Dave's CAD model he had visualized the wood as a perfect cylinder.  But As I worked the wood I felt that a rounded back would look and feel "warmer" to the touch.

Visit Dave's web site:
DAB's Clocks

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