A great friend of mine is going to PAX West as EDI, a character from Bioware’s Mass Effect 3. I helped her with the LEDs to illuminate the visor.
I was originally planning on deadbugging the whole thing — no circuit board at all, just inline splices, but the friendly EE at work told me it would make much more sense to use a perfboard, and would make things much easier. Boy, was he right!
The setup has 6 LEDs: 3 on each side, each with its own resistor, because I needed to keep the battery weight low (3 AAA). If I could have gone with higher voltage, I could have used fewer resistors, but this worked out pretty well. I used the LED Series/Parallel Array Wizard to calculate the resistor sizes, based on the info off the flat 3mm orange LEDs I got from ebay.
Here is what I did:
For wiring, I used cat 5e ethernet cable, which has 4 pairs of wires: each pair consists of a color coded set, one solid, one striped, that are twisted together (hence, ethernet cable being called “twisted pair.”) I trimmed the pair I wasn’t using close to the outer plastic shield and used the other 6 wires, 2 wires for each LED, one cable for each side of the visor. I stripped the cable down to the individual wires at each end for soldering.
I got a tiny (1.75″ square) perfboard from Radio Shack (again thanks to the EE for the suggestion) and soldered the 6 47Ohm resistors a few pegs from the edge of the board. Where the resistors would attach to the negative battery lead, I soldered all 6 resistors together in a huge blob. I then soldered the solid-colored wires (3 from each cable) near the edge of the board, and connected each solid wire to its own resistor.
The striped wires I cut longer and soldered in a line near the other side of the perfboard. These also got soldered together in a blob and connected to the positive lead from the battery.
The LEDs themselves were a bit more of a pain, partially because I was extra nervous about making sure I didn’t accidently connect the positive lead to the negative supply. Originally I just tried straight soldering the LED lead to the ethernet wire but things kept moving around, so I made a little loop on each wire and lead and hooked the two together, making a really solid mechanical connection. This worked much better, but I kept forgetting to take into account the longer positive lead, so I kept making a little loop of ethernet wire for the positive side to take up the extra space. At each step (individual soldered wire and each LED) I used heatshrink tubing to make sure everything was together as solidly as I could.
After testing, I covered the entire perfboard (front and back) with a ton of hotglue. Again, this was a suggestion from the EE, as it provides not only insulation for the components but some strain relief for the cabling. I used about 3 sticks! After I hotglued everything, I grabbed a small piece of foamcore that The Artist Wife was using for a project of hers and cut it to slightly larger than the perfboard and put it on the back (to further protect the solder traces) — the hotglue was tacky at this stage so it stuck nicely. Finally, I cut a piece of 1.5″ shrink tube to size and shrunk it on. I wanted to be sure that none of the components could possibly short out due to sweating in the helmet, and to provide as much protection and strain relief for the cabling as possible.
I’m pretty happy with how things turned out, and I learned quite a bit: I’ll be using perfboard for more projects, and I need to be more aware of the difference in the lead lengths (positive vs negative).
I hope my friend is happy!