Introduction: Make a Light Sculpture Using an RGBW LED Strip

By mirobo.tech
About: I'm a (mostly) retired high school computer technology teacher on a mission to create and share fun electronics, microcontroller, and robotics projects as chief human at mirobo.tech.

After getting a Laser-cutter I decided I'd like to apply my design skills to create a simple, lit-up Christmas decoration. I normally design and build educational microcontroller and robot circuits, so I had a few ideas for a small, simple, and multi-function lighting circuit that would be the lighting part of the project.

But, I didn't necessary want the lit-up design to only be suitable for Christmas, and I also didn't want the design to be limited to Laser cutting. So, while this version is laser-cut and Christmas-themed, it's entirely possible to use traditional woodworking tools, a 3D-printer, or many other fabrication techniques to make similar light up designs for all kinds of other events and occasions!

As you can see in the photos, what I've created is a two part design that I refer to as a light sculpture. The main part is the base, which houses (and hides) the lighting circuit and a strip of RGBW LEDs. The second part is composed of interchangeable sets of foreground and background objects for Christmas or other events. The LEDs in the base both illuminate the background objects and silhouette the foreground objects to create a simple and adaptable light sculpture scene.


Designing the lighting circuit

To keep the circuit small and as easy to build as possible, I settled on two main design goals: 1) it had to be powered by a commonly-available USB phone charger instead of needing a bulky battery pack, and 2) it should use an LED strip for simplicity instead of having to string individual lights throughout the design – although I won't stop you from wiring up individual NeoPixel LEDs if you really want to!

I based the lighting circuit on a larger, through-hole addressable LED driver circuit I had previously created for my grade 12 computer technology students called RAINBO, but simplified the circuit and re-designed it to use surface mount components to make it even smaller for this design. While thinking about the design, and how controls would normally be attached to a circuit board at the rear of a project, I decided to split the circuit into two parts to allow its one and only touch control button to be mounted at the side (or front) of a lighting project instead.


About the circuits

Each circuit is designed to be just 12.7mm (0.5") wide, or the width of the type of LED strip that has its LEDs encased inside a silicone sleeve – just slightly wider than a bare 10mm wide strip. If you've used LED strips before, then you'll know that they feature cut marks aligned with sets of copper pads in between each of the LEDs on the strip. These marks indicate where the strip can be cut to shorten the strip, or have its pads soldered onto another LED strip to either lengthen it, or to attach corner connectors for more complex lighting designs. In fact, the commonly-available 4m- and 5m-long reels of LED strips are composed of individual 50cm sections of LED strips that simply have their copper pads soldered together end-to-end to make a longer strip.

My lighting circuits take advantage of the copper pads on the LED strip by using a castellated board-edge connector to solder directly onto the strip. This also has the happy coincidence of reducing the number of individual wires that need to be connected between the circuits and the LEDs to zero!

The lighting controller circuit is called RAINBO-S, and uses a Microchip PIC12F1840 microcontroller to control the LEDs. This inexpensive little 8-pin microcontroller is programmed in C, and has an internal oscillator circuit, an internal capacitive touch sensing circuit, and just enough memory and speed to be able to create the necessary NeoPixel control signals. I added the ICSP (in-circuit serial programming) header to the RAINBO-S PCB (Printed Circuit Board) enabling it to easily be re-programmed using one of Microchip's PICkit programmers.

The second circuit is the RAINBO-P power connector circuit, and it consists of just a hand-solderable USB-C connector and the two 5.1kΩ pull-down resistors necessary to get an upstream USB-C host to provide 5V to a downstream device. I did actually solder a few of each of the RAINBO-S and RAINBO-P circuits together by hand, but I found this to be too tedious for making more than a few circuits so I opted to have a small batch of them assembled by PCBWay, and I'm making these pre-assembled circuits available on my website.


About the LEDs

Most 5V addressable LED circuits use the popular WS2812B 'NeoPixel' LEDs which have a built-in controller circuit connected to individual RGB (red, green, and blue) LED elements. Although these can be made to produce white light by turning all three LED elements on at equal brightness values, the light produced is often not pure white, but is instead a more blue-ish or green-ish white.

Since I wanted my light sculptures to have a nice-looking white in addition to all of the other the colours, I opted to use the newer SK6812 RGBW (red, green, blue, and white) LEDs instead. These are available in three different white-light 'colours': daylight (cool white), natural white, and warm white colour temperatures, and you can tell SK6812 LEDs apart from WS2812B LEDs by the large, yellowy, white-light-producing phosphor area visible in the window of the LEDs. For my build, I chose natural white LEDs, with a colour temperature of 4000°K, and have my program add just a bit of a warmer tone to them, as I found them a bit too cool for my liking without this. I opted not to use the warm white versions because I found them a bit too yellow for my taste.

Ok, ready to build the light sculpture? Here's how I created mine, and there are lots of other ways to make a similar design!

Supplies

Making a Laser-cut light sculpture

I designed these Laser-cut light sculpture bases to precisely fit three different sizes of RAINBO lighting circuits. The first one is small enough to be cut by almost any hobby Laser cutter with a 200mm or larger cutting bed, while the two other sizes for larger Laser cutters have been designed to fit commonly-available 300mm and 400mm sheet material.

You'll need enough material to make the four layers of the base, plus additional material to create all of the light sculpture objects that you want to attach to it. I used LightBurn to create the files, and both LightBurn and SVG files of the base and light sculpture objects are included, below.

  1. 3mm plywood or MDF designed for Laser cutters
  2. a 10-20W (or higher) Laser cutter
  3. LightBurn software (or other Laser-cutter software capable of using SVG files)
  4. (optional) card stock to create risers for the RAINBO PCBs
  5. wood glue (or glue appropriate for the base material) to glue the base layers together
  6. Small RAINBO-8 Christmas light sculpture design file (190mm width) - attached below
  7. Medium RAINBO-14-base design file (290mm width) - attached below
  8. Large RAINBO-20 base design file (390mm width) - attached below


RAINBO Circuits

For this build, I'm using my RAINBO-S and RAINBO-P circuits. These are pre-programmed and available either as a circuit kit that you solder onto your own SK6812 LED strip, or as a pre-made lighting circuit that includes the RAINBO circuits soldered onto a strip with a set number of RGBW LEDs.

RAINBO circuit kit - requires a separate SK6812 LED strip (RAINBO is programmed to use up to thirty SK6812 LEDs)

  1. sharp scissors
  2. electronic soldering iron
  3. electronic solder


Small RAINBO-8 lighting circuit (190mm base size)

Medium RAINBO-14 lighting circuit (290mm base size)

Large RAINBO-20 lighting circuit (390mm base size)


Alternative LED Light Strips

You can build a light sculpture using almost any kind of LED strip and its associated controller. Whatever kind of LED strip you buy, follow the instructions that come with it to shorten the strip to the length needed for your design.


Making a wooden light sculpture

You could use almost any kind of wood to make a base that holds the LED strip and lighting circuits, and then add pieces of thin wood to make the light sculpture objects. Here's one possibility that mimics the Laser-cut base, but you could also just as easily fasten the LED strip on top of the wooden base.

  1. 1" x 3" (approx. 5/8" x 2.5" actual size) to make the base (choose the length you'd like it to be!)
  2. 1/4" plywood or hobby planks to make the light sculpture objects
  3. a scroll saw or jigsaw to cut the light sculpture objects
  4. a router and 1/4" bit to cut one or more slots in the top of the base to hold the removable light sculpture objects, or just glue them on for a permanent light sculpture design (or rip-cut the slots using a table saw)
  5. a router and 0.5" bit to cut the wide slot in the bottom of the base to hold the LED strip (or rip-cut the slot using a table saw and dado blade)
  6. drill and drill bits to make individual LED holes in the base


Making a 3D-printed light sculpture

Obviously, having a 3D-printer means you're not limited to a basic design like the ones shown here. You can use an LED strip to light up almost any design you can imagine, including dioramas, shadow boxes, photo frames, book nooks, and much more! You'll only be limited by your CAD skills and imagination.

Attachments

Step 1: Assembling the RAINBO Lighting Circuit

Here's how I assembled the example RAINBO light sculpture. To make the RAINBO lighting circuit I started with the RAINBO circuit boards and an 8-LED length of an SK6812 RGBW LED strip with a self-adhesive backing.

  1. Use sharp scissors to cut the LED strip to length along one of its cut marks.
  2. Find the input side of the addressable LED strip. For all addressable LEDs, an external lighting controller circuit generates the LED data signals, and this data gets passed down the line from one LED to the next. Arrows marked on the strip show the direction the control data will travel.
  3. Match the castellated contact end of the RAINBO-S controller circuit to the input end of the LED strip. The '+' marking on the controller must go to the +5V line of the strip, and the '-' marking must go to GND or ground. The data signal is in the middle, between +5V and GND. If your strips don't match up like the one in the photos, then the RAINBO-S controller will not work with them!
  4. Carefully apply a small amount of solder to the data input (DI, or DIN) pad on the LED strip.
  5. Align the RAINBO-S circuit on top of the LED strip, so that about 1mm of the strip is under the castellated edge of the RAINBO-S circuit, and carefully heat both the circuit and pre-tinned pad of the strip while adding a small amount of solder to connect the data pin.
  6. After soldering just the data pin, check to make sure your solder is not shorting to either the +5V or GND connection, and that the LED strip and circuit are still in alignment. It's easy to reheat this single connection to fix any problems now, but very difficult to fix it after soldering all three connections later!
  7. Tin the soldering iron tip and carefully heat both the +5V pad of the LED strip and + connection of the RAINBO-S circuit while adding a bit of fresh solder to the area where they meet. Ensure the solder flows between the pad on the LED strip and the castellated contact on the circuit and makes a good connection.
  8. Repeat the previous step solder the GND pad of the LED strip and the - connection of the RAINBO-S circuit.
  9. Inspect your work, ensuring there are no short circuits between the three solder connections, and clean any residual solder flux (unless you used electronic solder containing a no-clean flux).
  10. Align the RAINBO-P circuit at the opposite end of the LED strip and verify its connections.
  11. Repeat the same steps used to solder the RAINBO-S circuit, first applying a bit of solder to the DO or DOUT pad in the middle of the LED strip and soldering the middle pin of the RAINBO-P circuit to it.
  12. Then, finish soldering the + and - contacts on the RAINBO-P circuit to their matching pads on the LED strip.
  13. Remove any residual solder flux and ensure the circuit is dry before plugging it into a USB source to test it. RAINBO is programmed to cycle between modes by quickly tapping and releasing its touch sensor. In each mode, holding or long-pressing and then releasing the touch button allows certain characteristics be changed.

Step 2: Assembling the Laser-cut Base

The Laser-cut RAINBO base is constructed using four layers of 3mm material, and its design enables a RAINBO lighting circuit to be embedded inside its two innermost layers. To maintain a clean appearance, slots are cut into the top layer only where objects will be inserted, even though all of the slots are cut by default on the inner layers (any of the unused inner-layer slots can be removed to speed up Laser-cutting).

  1. Before cutting, plan which top layer slots need to be cut for your design. Change these from a tool layer (in the LightBurn file) to a cut layer, and use the results of a material test done on your Laser to set the proper power level and feed speed for each layer of the file. Then cut the four layers of the base, along with the alignment tabs.
  2. After cutting, assemble the base from bottom to top. Start by carefully aligning layer B2 above layer B1, and glue layer B2 onto layer B1.
  3. Optional: You can install either a full-length riser, or two smaller risers into the long, RAINBO circuit cut-out in layer B2, depending on your LED strip.

 The photos show a full-length riser cut from a piece of cereal box material that will raise the self-adhesive LED strip higher up inside the base. For silicone LED strips, individual risers can be added under each of the RAINBO circuit boards to better match the height of the circuits to the height of the LED strip inside the silicone sleeve. Glue the riser in place.
  4. Make sure you've tested the lighting circuit before proceeding – it will be very difficult to remove it after layer B3 is glued on!
  5. Fit the lighting circuit in the long slot in the B2 base layer, and choose the best way to mount it. For self-adhesive LED strip, simply peel and stick the strip into place.

 Glue won't stick well to the silicone sleeve that encases some LEDs, but you can just place a strip like this into the into the B2 cut-out without any adhesive, or use double-sided tape or low-temperature hot glue to fasten the circuit boards to either the base or the circuit risers.


  6. Carefully align layer B3 above layer B2, and glue B3 onto B2, and temporarily insert two or more Alignment Tabs into matching slots in both layers to prevent the layers from shifting while gluing. Be sure not to accidentally glue the tabs into place! Remove the alignment tabs once the glue has dried.
  7. Next, carefully align layer B4 above layer B3, and glue B4 onto B3, re-using the Alignment Tabs as in the previous step. Remove the alignment tabs after the glue has dried.
  8. If you want to paint or apply another kind of finish to the base (leaving the light sculpture objects removable), you can do that now.


Step 3: Creating Light Sculpture Objects

Next, it's time to create some light sculpture objects for your base. You can use the ones included in the design files, or create your own using these suggestions:

  1. place tall background objects in the slots behind the LED strip to create a light-reflective surface that silhouettes your foreground objects
  2. light sculptures should look great in the dark too, so rely more on the shapes of the foreground objects to create the scene than putting lots of detail on the fronts of the objects
  3. make creative use of holes in foreground objects to allow the backlight to pass through them
  4. layer foreground objects in multiple rows to provide visual depth in your scene
  5. when designing the objects in your light sculpture scene, align them with the slots in the RAINBO base file (or copy the slots from the base file and align them with your drawings) to see the fit and relationships between the objects
  6. if your base has extra slots cut for one light sculpture design that aren't needed for another, consider creatively widening smaller objects to cover an unused slot and fill the ‘holes’ in the design
  7. don't glue the light sculpture objects into the base when creating interchangeable designs, or when making light sculptures that can be disassembled for storage (important for seasonal designs)

Fit the light sculpture objects into the base, and it's ready for display! The RAINBO circuit has an adjustable white light mode, a mode that lets you set it to produce any colour, a colour-cycling rainbow mode, and a simulated aurora mode, and you can find other LED strips and controllers with even more lighting possibilities.

Thanks for following along. I hope this might inspire you to make your own light sculpture!