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Victorian Wallpaper Shadow Sconce

by marciot, published

Victorian Wallpaper Shadow Sconce by marciot Jun 19, 2015

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License

GNU - GPL
Victorian Wallpaper Shadow Sconce by marciot is licensed under the GNU - GPL license.

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Summary

A wall sconce that projects a Victorian wallpaper design on the wall. Dozens of ways to customize and prints great on consumer FDM printers!

Instructions

This project involves soldering, small-parts and electrical components. You assume all risks and liabilities should you wish to undertake it.

Print it:

The sconce is a single plastic part. The cutouts have extremely fine details that may exceed the resolution of your printer. Even though some of the details will be filled in, the final shadow will still capture the essence of the pattern and should still look good. Don't fret the details -- all my test prints were done successfully with a consumer FDM printer at 0.2mm layer height and retraction enabled. I'm very pleased with the results!

Support is necessary for the arm but is not desired for the sconce body as it messes with the details of the cutouts. I added a brim underneath the sconce walls to prevent Cura from printing support in that region. Set "Support type" to "Touching buildplate" so that the the arm will get support but the sconce walls will not.

Light it up:

My LED was a de-domed Cree XM-L2 on a 16mm star (de-doming is the process of removing the silicon lens, which can reduce the apparent size of the LED). This LED was probably oversized. I am not able to run it at anywhere near the max current and the shadows aren't as sharp as I would have liked.

If I were to do it again, I would have tried a LED with a smaller die size to sharpen my shadows. A smaller LED would also eliminate the need to de-dome the LED, which is a delicate, possibly destructive step, so I would recommend you start with a smaller LED like the Cree XP-E2.

Power it:

The LED will run off 3-4V, so you will need a suitable power supply. I used a recycled 12V wall wart combined with a adjustable micro DC-DC step-down converter from e-bay. The particular one I used was listed as "10pcs Mini DC-DC Converter Step Down Module Adjustable Output 1-17V for RC PLANE" and sold by axeprice. This DC converter is really tiny and fits into the cutout I made on the backside of the sconce. The converter has an adjustable output voltage, so you can tune the brightness of the LED and balance it against heat generation.

Cool it:

My LED came mounted on a 16mm star. This provides some degree of cooling, but you can get more cooling with a heat-sink. I removed the rubber liner from a bottle cap with a heat gun and mounted my LED to it using Arctic Alumina thermal adhesive. This gave me additional cooling while still being low-profile enough to fit inside the sconce.

Assemble it:

Assembly consists of soldering the various parts together. Be very careful about the polarity of the components. The following build sequence worked for me:

  • If you are going to use a bottle cap heat sink, remove the liner from the bottle cap and attach the LED to it using thermal epoxy.
  • Solder wires to the LED + and - terminals. Your wires need to be long enough to reach from the front wall of the sconce, through the hole in the support arm, all the way to the base. Leave a few inches of slack so you can solder the other end easily.
  • Cut the plug off your AC wall wart and solder the wires directly to the input pads of your DC-to-DC converter. Use a multimeter to determine which wire is positive and which is negative if you cannot tell. Polarity is very important.
  • Plug in the AC wall wart and adjust the voltage on your DC-to-DC converter to a safe value such as 3V. This will keep you from blowing out your LED when you first power it up.
  • Solder the end of the LED wires emerging from the back of the sconce to the output terminals of the DC-to-DC converter. A set of bench top helping hands is very good for this task. Mind the polarity -- if you get it reversed, the LED will not light.
  • Stick the double sided tape to the backside of the LED or bottle cap and use a marker to make a dark dot on the back of the foam-tape directly opposite the LED center.
  • Positioning the LED is critical for the shadows to look correct. There is a small peep-hole on the front of the sconce to help you find the correct location.
  • Look through the peep-hole as you manipulate the LED inside the cup until you see the black dot on the tape.
  • Align the dot with the hole to ensure the LED is dead center and press it down to stick.

Tune it:

Once you first plug it in, run your sconce and monitor it to make sure the LED is not overheating. If it is, dial back the voltage on the DC-to-DC converter. You want the LED to run warm, but not hot enough to melt the plastic or cause a fire hazard. Do not run the sconce unattended until you have monitored it for several hours to make sure heat is not a problem.

Customize it:

The sconce and wallpaper pattern is customizable. You can do modifications online using the Customizer. For even more complex patterns, download the OpenSCAD file and follow the instructions in it on how to convert any SVG file from Inkscape into a wallpaper pattern.

Be aware that not all wallpaper designs are printable (at least not on a FDM printer). There cannot be islands or downward hanging points in the cutouts. For example, the letter O has an island that cannot be printed and a heart symbol has a downward hanging point on the top that cannot be printed. Non-printable designs can sometimes be fixed by adding vertical supports or breaking them up into parts. Getting a good design takes care. The ones I provided have been tested and give a good print.

Credits and Inspiration:

  • Ornate medallion wallpaper design by Jakub Jankiewicz (kuba), public domain.
  • Inspired by stereographic projection ideas of Henry Segerman and Saul Schleimer

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Do you think the Cree XP-E2 would be ok powered by a USB 5v power supply without the transformers?
Alternatively, could the base be carved out to make room for three AA or AAA batteries?

You would not want to connect the Cree XP-E2 directly to your USB port. It is a diode and would short out your USB port. Either the LED would burn out, or your USB port would burn out, which ever came first.

You would need to have some sort of current limiting. A resistor would be the easiest way to make it work. I have attached the spec sheet for the XP-E2:

http://www.cree.com/LED-Components-and-Modules/Products/XLamp/Discrete-Directional/XLamp-XPE2

The key specification here is the Typical Forward Voltage, which is 2.9 V White @ 350 mA. So you would have to choose a resistor to put in series with the XP-E2 such that 350 mA would flow through the circuit. There would be a 2.9V voltage drop across the LED, and a 2.1V voltage drop across the resistor in that situation. While a USB port can handle the required wattage, you would need at least a 1W resistor to dissipate the heat generated.

You would have a similar problem with AA or AAA batteries. If you simply connect three batteries directly without current limiting, you would blow out your LED or overheat the batteries, so you need to choose a resistance properly to keep the current at or below 350 mA.

If you don't know how to do this, I recommend getting a basic electronics book, such as Forrest Mims's "Getting Started in Electronics" to get a basic familiarity with how to power LEDs.

And if you do experiment with this, start out by using a cheap USB charger, as you don't want to fry the USB ports on your PC if you make a mistake :)

Thanks for the lessons! I was intending to use a USB charger from an old phone. Can I ask how your method adds a resistor? Does the DC transformer take care of it?

No, but the voltage is adjustable on my DC-to-DC converter, which sits between the power brick and the LED. So the output voltage is tuned to approximately 2.9V, which gives the correct operating current for the LED.

The repurposed transformer (power brick) provides an intermediate voltage (typically 6V to 12V) and the DC-to-DC converter steps it down precisely to 2.9V.

A resistor can be used in place of the DC-to-DC converter, but is non adjustable and needs to be selected for a particular input voltage. The DC-to-DC converter is adjustable and more flexible, but is more expensive. It may have difficulty operating with an input voltage of 5V, but if you find one that works with that, you could use it from USB power. No resistor or power brick needed, as long as you tune the output of the DC-to-DC converter to less than 2.9V.

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