Laser Cut Constellations

A 2D Design + Circuit Building Activity for Teens & Adults

At the Makers in Motion summer camp in Peoria, IL, the CUCFabLab team tried out a new activity to complement the camper’s visit to the museum’s planetarium. At the end of the camp, we had a whole sky-full of glowing constellations. The creative soldering abilities of 7th and 8th graders surprised us — this was just a day after assembling their first ‘blinky badge’!

The afternoon started by asking the class what they learned during the planetarium show. There was some conversation about stars burning at different intensities with different colors, and some review of how red-shift and blue-shift are used to determine the movement and velocity of stars and galaxies.

We then asked if anyone had a favorite constellation, or if they knew any mythical stories about them, but that didn’t get very far. So, we let everyone open their laptops and pull up the wikipedia’s list of constellations. (You know, I just realized how nice it is to have a laptop-based computer lab, since you get to dictate whether people are looking at computer screens or each other. You’re much less likely to look across the table or up at the instructor if you have a computer screen in front of you already.)

Everyone was encouraged to read through the descriptions and mythologies of different constellations for about 10 minutes before we would go around the room and share what we learned. This was pretty fun — the wiki articles often have nice art and interesting origin stories for the students to share with each other (we didn’t discourage looking over each other’s shoulders). When time was up, we asked each student what constellation they chose to look at and if they could tell us a little about it. Some people had constellations with very intriguing mythologies (Anything involving the god Jupiter gets pretty crazy) and we had some laughs over the absurd story lines of Greek gods.

What followed was our standard intro to Inkscape: here’s how you can draw circles, here’s how you can draw lines. You can turn circles into lines and vice versa. You can copy paste pictures, and turn those into lines, too! Oh, and all those lines we have? We can have our 30 watt laser beam follow them for us.

The most difficult part is finding suitable constellation art with a strong border to trace using Inkscape’s “trace bitmap” feature. A few of the outlines had to be drawn by hand with the Bezier Curve / Line tool — the snake and the big dipper come to mind — but that’s a good learning experience, too. After we had the outline, we went through the process of creating the cut outs the LEDs pop into.

Create a 0.9 mm circle
Duplicate that circle and move it 3 mm away (using the X and Y coordinates at the top of the program)
Group the pair of circles
Copy paste the pair of circles anywhere you want to place a star/LED

Edit, 6 months later: Really great constellation art can be found on wiki, here:

https://en.wikipedia.org/wiki/Urania%27s_Mirror

Students who finished that early were asked to draw red lines between the stars forming their constellations that could be lasered at low power (or in one case, trace an outline of the ram with a red line since all of its stars surround it.) When the files looked like they were coming together, we had everyone save their inkscape file to a shared folder on google drive. Only do this if you have really good internet! A locally networked shared folder would do the trick, too. It’s always fun to see the kids’ names fill up the folder on the instructor’s screen so we can make sure everyone got their file in the same place.

After snack we wrapped up the day by learning how to solder with the ever-popular Blinky Badge! That night Virginia and I checked each file for proper line weight and color (our Epilog laser likes to have 0.001″, solid black lines) and compiled all the Inkscape files into two cut files we could knock out the next morning.

The next day the kids were greeted with wooden versions of their digital designs. To start the electronics portion of the project, we asked the students to review what they knew about circuits and the blinky badge — just that you’ve got a battery with + and -, and you’ve got an LED with + and -. We passed around batteries and LEDs of different colors and let everyone experiment. Pretty soon they figured out you can put multiple LEDs on one battery. (Check out the super-informative Evil Mad Scientist blog for reasons why this works out OK without the ‘proper’ resistors in series.) We also stumbled upon the question of why you can’t mix colors —remembering that elecricity will take whatever path requires it to do the least amount of work and some colors like red and yellow take less voltage to illuminate than others like blue and white. Hey, that’s kind of like how cooler, less energetic stars are red and yellow while hotter, intensely burning stars are blue and white. Probably just a coincidence and nothing to do with band gaps and photon wavelengths. (You get to decide if you want to bring up band gaps and photons with your age group!)

So everybody knows all the positives have to connect and all the negatives have to connect and they can’t touch. Next step was to design the circuit that would connect the LEDs in their constellation. We passed out red and blue markers and asked everyone to trace their constellation on paper and then mark where their stars are by eyeballing it. This was presented as the puzzle it is: how do you rotate each LED in its place and run a piece of copper between all of them so that they connect without crossing wires? (Or, at least avoid it as much as possible. Everyone learned that electric tape is a very useful insulator if you don’t want two pieces of metal to touch.)

Like I said, I was really impressed with everyone’s problem solving and stick-to-it-edness on this task. Kids even commented that it was fun! I think the imminent danger of things burning along with the puffs of steam and being trusted with a soldering iron made this a really good experience for everyone. If you’re planning on doing this activity yourself, make sure you enforce the rule to put your soldering iron away if you’re not actively melting something. The only injuries I’ve ever seen in teaching people to solder (2 minor burns in hundreds of students) is when you get distracted and forget you’re holding a burn-stick. To accommodate our kid-to-iron ratio, students had to share, and we also made sure everyone knew not to hand the iron to each other — put the iron back in its holder and let the other person pick it up. Take a close look at the pictures of the solder joints, even when tape overlaps tape its important to join them with a dab of solder as the underside of the tape is non-conductive adhesive. Sometimes you can avoid tape altogether if your LED’s leads reach each other.

There were just a few (maybe 3 or 4 out of 15) that had some persistent problems getting illuminated, but even those kids stuck with it. We were lucky enough to have about 3:1 ratio of teacher-helpers and even if they couldn’t find the error right away just helping the student inspect the circuit for problems helped them persevere. Most of the problems were just weak connections somewhere along the line, solved with another dab of solder. I think the hardest to track down problem we had was one where copper tape was stacked above electric tape stacked above the opposite copper tape, and when soldering on top of this sandwich, the copper absorbed enough heat to melt through the insulator in between, but just enough so we didn’t see it until totally disassembling that part of the circuit.

For display, the finished products were taped to black foam core and its wires (jumper cables soldered on after the fact) stuck through to the back. Arduinos were programmed to blink and fade the constellations. When they’re taken home, they could still be illuminated by AAs or button cell batteries.

Here’s a video of the FabLab portion of the camp that includes these constellations.