Shooting Stars

This is an all-DIY project that provides an opportunity to use a 3D printer to create a nifty lighting effect. It's not a hard project, but it's a bit of a time-consuming one depending on how many "stars" are incorporated into the display. For this project, the author designed a 24-star line with stars approximately 1 foot apart. The goal was to create a display piece that could be wired from the ground up to a larger main star mounted in a tree or on a garage roof so that it would appear like an eye-catching "swoosh" of light rising up to the main star. Therefore, each star in the line also needed to have individual control.

It was thought that while a string of pixels could certainly be used to accomplish the animation function, the individual pixel bulbs weren't large enough to be truly eye-catching. But pixel technology could certainly be used -- just not with individual bulbs. And since color wasn't important, a project similar to the monopixel candy canes (MonoPixel how-to is HERE) seemed appropriate.

• First, a star had to be made. This proved to be quite easy on Tinker Cad (http://tinkercad.com) which provides a basic star shape in their built-in tools. It was enlarged to approximately 4" across and the center raised. Then it was duplicated on the screen; the duplicate was reduced in size by about 1.6 mm in all directions, set to be a "hole" and simply merged into the first star. This resulted in a thin star "half-shell" that when two stars were glued together, would provide plenty of room for electronics inside yet allowing plenty of light to shine through. For the 24-star display, 48 half-shells were required. (Note: printing time was a bit over an hour each which is why this project takes some time... The STL file for this star is inside a ZIP file and can be downloaded here: DOWNLOAD STL FILE

• The electronics inside the stars were simple: five clear white LEDs soldered onto a two-sided piece of spare PCB stock; anodes soldered to one side; cathodes to the other and a lead wire soldered to each side -- all 5 LEDs would be electrically parallel. The wire used was a pair of wires stripped from a length of CAT5, chosen for low-cost and ability to easily handle the tiny current needed to illuminate the leds. The individual stars would be soldered to the R, G and B outputs of the small WS2811 PCB board that square pixels use.

• A prototype star was assembled and tested for feasibility before investing more time in the project: VIDEO The prototype electronics were also tested without the star shell and it was decided that the LEDs' lenses were too directional and more light would be captured with the star shell than without it.

• Being adequately bright, two more stars were printed and one complete segment of 3-stars wired to an inexpensive WS2811 board designed for square-base pixels using the board's RGB and +V connections. The square pixel board has all the necessary components for LED current control while also supplying 18.5ma of current to each of its three outputs.

A video was made of the prototype test: VIDEO A second video was made viewing from a 25' distance in darkness. We liked the result: VIDEO and we decided to start printing more star shells.

• We determined that a wiring harness might be helpful to make this project a reality. And since it had been decided the stars would be 1 foot apart forming a 24-foot line of stars, this required eight 3-foot long segments comprising one square pixel board and three, 5-point LED boards. The segments would then be attached together to form the 24-foot line. While the star shells were being printed, a wiring harness was constructed. We chose 4-conductor telephone wire for the main cable primarily for its strength but also because it had a smaller diameter than CAT5 and might be less visible. But CAT5 wiring was used for the LED connections to the square pixel board -- we chose the orange, green and blue wire pairs to represent the red, green and blue colors. As the square pixel boards use common-anode RGB Leds, the solid-colored wires would be soldered to the cathode side and the striped wire to the anode side of the 5-point LEDs (the WS2811 chip is a current sinking device). Important: For the sequencing to work consistently, the order of the wires in the harness should match the WS2811 chip, which is RGB and each 3-foot segment must be wired the same way. The harness made, we focused on printing the 48 half-shell stars we needed...

• After attaching the LEDs to the harness, we were excited to view our harness test: VIDEO And for reference, here's a diagram of the connections for one segment of the harness:

...but...at this point, the project completely stalled-out after 17 shells had been printed. Problems with the 3D printer had developed and we were unable to resolve them for several days. However, the project resumed after it was discovered that the plastic filament material had become stuck inside the printer's feed tube. Following cleaning and replacement of the tube, printing resumed but this time, using a different filament material. We had started the project with ABS filament and we thought the higher temperature ABS requires had helped to cause our problems. We changed to a similar color of PLA filament. Since the completed stars will be sequenced to run in a rapid "swoosh" action, we decided the filament change wouldn't be an issue. The photo below notes the color difference of the PLA vs. ABS material

• Gluing the star shells around the 5-point LED board proved to be somewhat putsy. For one, we discovered that when we put them back-to-back, the star shells didn't line up in perfect registration like we originally assumed: they were generally slightly off but by trial-and-error, we always found a best fit that was quite excellent. (We believe this to be an anomaly with the 3D printing process -- perhaps our printer's X-Y axis settings are a little off.) We used E-6000 glue with rubber bands to hold the star together while the glue set. (Note that the edges of the star are easily sharp enough to cut rubber bands -- we went through several.) E-6000 glue is really terrific stuff; it's similar to silicone glue or GOOP, but once set, is still slightly flexible and incredibly strong.

• It was always our intention that the harness would be wrapped with some sort of protective tape, and we secured some "harness tape" from Amazon. It was inexpensive, has a flexible cloth base, doesn't stretch, has excellent adhesion and being black, we thought that might hide the wires even more. An additional benefit is that the tape is tough as can be -- it doesn't even cut easily. We wrapped the entire line with it and we think this will not only help protect the electrical connections, it will also have the effect of making the overall wire stronger. But... there goes the idea of having a thin wire... the tape makes it a lot thicker...

• After the project was fully assembled, we were a bit taken back by the overall weight. This gave us concern that the six solder points on each of the 3-LED sections could suffer from undue stress, especially in windy conditions. We decided that short sections of Boscoyo's pixel mounting strips (http://boscoyostudio.com), trimmed-down a bit and affixed to both sides of the junction would be helpful to stabilize the joints and minimize stress. Pictured below during application, they were positioned along the flat side of the square pixel PCB and later tightly wrapped with the harness tape. This resulted in a noticeable bulge at each of the 8 junctions but overall, a much stronger cable.

• The Controller for this project is simple -- most any pixel controller can be used with the understanding that normal pixel colors don't apply to the actual colors but they do apply to the position of the stars. Since the line of stars was wired in RGB order, the stars will also fire in RGB order. Lighting all "red" stars will light stars #1-4-7-10-13-16-19-22 of this 24-star "string." Therefore, the whole 24-star string comprises only 8 "pixels" in the configuration of the sequencing software. Our controller is a DIGWDF MiWiFi controller and a 5-amp, 5vdc power supply inside a compact, CG-500 case. (Note the added "heater bulb" next to the power supply; we include those in our controllers because of the severe sub-zero winter temperatures in our area that most power supplies don't like.)

• Two of the stars had yet to be printed when this video was made, but we were pleased with the effect: WATCH VIDEO After assembly is fully complete, each star will be checked again to verify that each is sealed shut to prevent water intrusion.