'We shape our buildings; thereafter they shape us.'

Winston Churchill

Some buildings have profound meanings and invoke powerful feelings within us. These buildings not only reflect the aspirations of the people who designed them, the determination of the people who built them, but also recount stories of the people who occupied them.

My appreciation of old architectures stemmed mainly from the influence of a good friend of mine. During her extensive travels in France, she came to understand and eventually fell in love with Gothic architecture. Nothing typify Gothic architecture than the magnificent cathedrals. Her birthday is around the corner. I am planning to make her a gift that will serve provide her with her very own little piece of Gothic architecture even when she is not on her travels.

During our numerous chats, she always recounts her lasting impression of a particular cathedral in France - Chartres Cathedral (Basilique Cathédrale Notre-Dame de Chartres). It is a cathedral located in the town of Chartres, approximately 80km from Paris. A little internet search quickly reveals why that is the case. The cathedral is simply stunning. One of its most notable feature, this true of most Gothic cathedrals, are its rose windows. The above last two photos shows the massive north rose window.

Upon seeing the two photos, the idea for the design of the gift is complete. I will build a rose window themed night light based on the Chartres Cathedral's north rose window. It will be a simple laser cut wooden box with the motif of the rose window in front. Light will shine through it through a piece of deep ocean blue acrylic. When it comes to the lighting, I have the image that during medieval times, on the cold and dark evenings of winter, the flickering candle light in the cathedral can be seen by the town's people through the rose window. So this night light will try to replicate that.

The stage is set for the design and build.

Step 1: Parts Needed.

The dimensions of my design will largely determined by what materials I can find in the local arts supplies store. Here is the materials I got for the project and some existing electronics components I have lying around -

3 pieces of 12"x12"x6mm plywood
3 pieces of 12"x12"x3mm plywood (only 2 needed)
A piece of translucent blue acrylic of larger or comparable size to the plywood
Wood glue
Sand paper
3 ultra bright leds
1 breadboard
Jumper cables
An Arduino (UNO in my case)

Step 2: Designing

The front face of the night light will be slight smaller than the 12"x12" of the plywood. This is to allow me to have some clearance when laser cutting the final design.

Fortunately a very good guide for drawing this particular rose window is documented by Michael S. Schneider in

http://www.constructingtheuniverse.com/Chartres%20...

Following the instructions, I drew the design in Solidworks. I think the instruction is probably suited more for being hand drawn. After drawing the design, quite a large amount of time was spent trimming off the unwanted lines. I then used the 'offset entities' command to create a 1mm inner offset to all the patterns in the sketch. After further trimming, I am left with the intricate design of the 'support' in the rose window each with a thickness of 2mm. To accentuate the outer ring of the window, I trimmed off the four comers and filled it in with some self interpreted design for the supports.

This rose window is supposed to be 'inverted'. Inverted in the sense that one can see both the supports and the shape of the stained glass windows. I drew the shape of the cut-out representing the stained glass windows with the previous design as a template.

I also drew a simple square big enough to cover all the cut-outs representing the stain glass windows.

For the rest of the box, I simply designed an alternating square pattern so that the pieces can fit together like a puzzle. Usually for this laser cutter, in order for a tight fit, the dimension of the slot should be 0.1mm smaller than corresponding key on all sides. However I figured since there are some many interlocking keys and that I am going to use wood glue anyway, the fit should be tight. Spoiler Alert! This is not the case.

I 'extruded' the sketch by the thickness of the plywood I am going to use to create the part. The assembly is depicted in the exploded view. I chose a face-on view and save the files as .dxf needed for the laser cutter. For the smaller pieces, I actually drew in the dimensions of the plywood material and 'assembled' them in an arrangement on the plywood material that minimizes material wastage. I then 'remove' the plywood material from the assembly, converted the assembly file to a part file and save it as a .dxf

Step 3: Fabrication

Nothing much in terms of fabrication, the plywood panels are just laser cut. I have engraved a personal message to my friend on the top panel of the box. Engraving may cause charring on the wood surrounding the engraved pattern. One possible way to reduce this is to put a masking tape over the area to be engraved. However I skipped this step for this project. I will probably try this for some other upcoming projects.

For post processing, I used a damped fine bristle toothbrush with some water and mild soap to go through all the laser cut surfaces to remove any loose charred residue. As one might imagine this took quite a long time for the outer front panel.

For the browning on the surface, I went though them with a sandpaper. The result particularly good for the engraving as the words looks clean after a few round of sanding. Finally I test assembled the pieces. As feared, but not detrimental to the build, the fitting is slightly loose.

Step 4: Assembly

I spread a thin layer of wood glue on the inner surface of the outer panel. Using the side pieces as jigs for alignment, I glued both pieces together. I then use double sided tape to fix on the blue acrylic sheet at the back of the window. The sides are then glued on in a similar fashion using a set square to make sure everything is at right angle.

The circuit for this project is exceedingly simple. I connected 4 ultrabright leds with their anode in parallel. The cathodes are connected to pin 6, 9, 10, and 11, the PWM pins. Normally, I would have routed out a PCB for this. But in the name of completing the gift on time, a breadboard with jumper wire does not hurt. I have also left out the current limiting resistors. My rationale for this are, 1. the turn on voltage for these blue leds are about 3.6V. 2. Given they will be powered by a randomized voltage to replicate the candle light effect, I do not think leaving out the resistor will significantly reduce their lifetime. I taped a piece of paper in front of the leds to serve as an added light diffuser.

I loaded the attached code onto the Arduino. Basically the code sends out a randomised PWM voltage to the pins with a period of 100ms. I experimented with other length of periods but the flicker looks unnatural. The lower limit of the PWM voltage is also set to just slight below the turn on voltage of 3.6V to ensure there is not significant period where the led are not lit. The result can be seen here in the video. I have to say the fickering looks better in real life than in the video.