DABs Clocks is a collection of hand made, one of a kind devices that each display time in unconventional and interesting ways. These time pieces are both functionally and aesthetically pleasing. I design and build some of my clocks without any assistance. For others I turn to Guy Marsden for the engineering and fabrication phase. In these situations I bring a concept to Guy and through an iterative and collaborative process I'll eventually create a 3D representation of the clock that Guy will build.
Cosmos:
Projection Analog Clock
Cosmos works by projecting the image of a 12 LED NeoPixel ring onto a round frosted acrylic screen and thereby tells time to the nearest 5 minutes. Hours and minutes are denoted by blue and red LEDs, respectively. When the hour and minute LEDs overlap the color seen is purple (blue + red). The time lapse video below shows the clock at work. The NeoPixel ring is located in the base and above it sits a 50mm Pentax camera lens (circa 1971) resting atop a set of extension tubes. The lens focuses the images of the LEDs onto a mirror that is set at a 45 degree angle to the optical axis of the lens. The mirror then projects the image of the NeoPixel ring onto a round frosted screen. The electronic clock mechanism and coding is identical to that used in Mushroom Zoom except it runs backwards given that the mirror introduces a left to right flip of the NeoPixel ring image.
Clock showing 7:20
Shows time advancing at approximately 100X actual speed
Blue dot = hour and Red dot = minutes
Time changes every 5 minutes
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Final 3D rendering Used to Guide the Engineering and Fabrication
The Build
8/32 thumb screw
Key Components
1) Lens
50mm f1.4 lens attached to 3 extension tubes. I've had this lens since 1971 when I got my first new camera-35mm SLR Asahi Pentax.
2) Mirror and Stand
Plymor Round 3mm Beveled Glass Mirror (4" diameter) from Amazon (https://www.amazon.com/gp/product/B07T56PPLZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1)
An adjustable (up/down) vertical post (5/16" diameter stainless steel) is fixed to a "floating base" (1/2" thick Black Opaque Chemcast Acrylic; TAP Plastics- https://www.tapplastics.com/product/plastics/cut_to_size_plastic/acrylic_sheets_color/341). A horizontal post (5/16" diameter stainless steel) extends from the vertical post and is linked to the mirror assembly such that that the mirror can be moved forward/backward and rotated in order to establish the correct 45 degree angle between the mirror surface and optical axis of the lens. All posts made of 5/16" diameter stainless steel.
4) Projection Screen and Stand
Frosted Satinice clear acrylic disc- 4.5" diameter and 1/8" thick (TAP Plastics).
An adjustable (up/down) vertical post (5/16" diameter stainless steel) is fixed to a "floating" base (1/2" thick Black Opaque Chemcast Acrylic).
4) 12 LED RGB NeoPixel ring (Adafruit; https://www.adafruit.com/product/1643). The ring is controlled by the same electronics used for Mushroom Zoom although in this case chip is programmed to run counterclockwise given that the mirror flips (left/right) the image of the ring.
5) Glass Dome
8" x 12" from Collecting Warehouse (https://www.collectingwarehouse.com/)
6) Base
Comprised of two layers of 1/2" thick Black Opaque Chemcast Acrylic.
The Projected Image of the NeoPixel Ring
In order to achieve the proper projected image (3.25" outer diameter and striped appearance of each LED) it was critical to correctly set the distances between all the components (NeoPixel ring to back of lens; center front of lens to center of mirror; center front of lens to center of projection screen).
Multiple prototypes were built using Legos and an adjustable mirror support. Adjustments were made until the desired projected image was achieved. Measurements were taken and a final prototype (no more Legos) was then constructed.
Final Prototype
Evolution of Cosmos Design
Several different cases were rendered in 3D before settling in on the general form designated by the asterisk(*).
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Determining Size of the Glass Dome
I placed the final prototype on an image of concentric circles and determined that everything would fit perfectly inside a dome with an inside diameter of 8". Fortunately I was able to purchase a dome that was 8" (ID) x 12" (H).
Optimization of Clock Accuracy
Accuracy is adjusted by altering the number of fixed length delays programmed to occur during a 5 minute interval. This is an iterative process and each time the code is adjusted a time lapse video is used to measure accuracy. Below is an example of such a video (it runs backwards because it is not being viewed through a mirror). When viewing the time lapse at 0.25x one can readily determine the time elapsed between each hour and measure the accuracy over a 12-24 hour period of time. The elapsed time on the clock is compared to the elapsed real time shown along the bottom of the video.
