Intro: Laser Mohawk
Last year I went to Burning Man and made this laser mohawk which I attached to a hat I'd made some time ago (the hat is from a dragonfly costume). It was quick to make and looked really fantastic at night with some dust in the air. The lasers shot out visibly from my head exactly as I'd hoped. Unfortunately I don't have any pictures of it there!
I used eight fingertip sized lasers which I got from Aliexpress, in a bulk order with a bunch of other people a year or two ago. Additionally I used three AA batteries and a plastic battery holder for them, some scrap black leather, a rocker switch, hot glue, and solder. Tools needed were only scissors, a razor blade, a soldering iron, and a sewing machine, although the sewing is minimal and needle and thread would be just fine too. I also used a breadboard for testing the electronics, but you could get away without this and just hold the leads together by hand or with a clip.
Step 1: Test Lasers
First I put all the lasers in a breadboard, attached a battery pack and switch, and verified that they all worked, and were bright enough with the 3 AA batteries I wanted to use. These particular lasers are low-power enough that there is no risk of accidental eye damage (you'd have to stare directly into one for quite a while before it had any chance of burning a retina) and 4.5 volts powered 8 of them just fine.
Step 2: Prep the Band and the Lasers
I used a couple layers of black leather that I had some scraps of. I originally was going to use many layers to support the lasers so they'd stand up vertically, but it turned out not to be necessary; one base and one cover strip was enough. I made a wooden jig to cut holes and glue the lasers so they'd be in the same place. Using a leather punch the same size as the laser tubes, I punched eight holes in one of the strips (a hole punch, if it wasn't too dull, would also have worked). Leather is a bit stretchy so the holes could be a little smaller than the laser tubes and still fit over them.
Next I marked on the base strip, where each laser would attach. I marked on the laser lead wires where I would solder them together to power them all in parallel. Then I cut the leads at the longer markings and stripped a quarter inch off the ends of each lead, leaving the last set long to attach to the switch and battery.
Step 3: Solder and Glue the Lasers
Very carefully, using a razor blade, I scraped off a bit of the wire insulation at the points I'd marked. The first laser has no previous one that needs to attach to it, so you can skip doing that one. I didn't think of this in time so I had unnecessary scrapings on it. Note that this isn't the one with the long leads remaining -- that's the last laser! It needs to be scraped.
One at a time, I hot glued each laser onto the band at the X marks I'd made. As I went, I soldered the previous laser's leads to the scrapes on the current laser's leads. Black to black and red to red; lasers are polarized. Once they were all glued and soldered, with the long lead laser last (LLLL for short), I tested again using the breadboard to be sure my soldering was all good.
Then I hot glued over the solders for insulation, placed the leather strip with the holes in it over all the lasers to cover the wiring, and glued that down.
Step 4: Switch and Battery Pack
To hold the battery pack, I cut a piece of leather a little bigger than twice the size of the pack. I folded it in half, leaving one half a bit longer as a flap, and sewed around 3 sides to make a pouch, into which the pack fit snugly. I stitched the pouch to the end of the laser strip, at the flap end where there's that bit of extra leather. Next I soldered the positive lead of the last laser, which was sticking out of the strip, to the positive lead of the battery holder (take the batteries out while soldering). I cut these short enough to fit closely, still allowing the battery holder to fit into the pouch, but left the negative leads longer to deal with the switch.
This switch is actually a lot bigger than necessary, but it is what I had lying around. A small slider switch would have been better, but anything that's not heavy enough to fall off the leather band is fine. Mine had leads attached, which I removed, but most don't. I soldered the battery pack negative lead to one of the switch terminals, and the laser negative lead to the other. It doesn't really matter which is which as all the switch is doing is opening or closing the connection between them. If you have three terminals on your switch, you'll want to choose two by testing. Usually you want the middle terminal and one of the end terminals, leaving the other end terminal unused (if you look closely you can see that my switch actually had space for a third terminal, on one end, but it has been removed).
After this soldering, test again with the batteries, and if all is good, go ahead and hot glue the switch down. Also put hot glue over the solder joins, for electrical insulation.
Finally, attach the strip to a hat! A hard hat would provide excellent support (you might want to use a couple additional lasers), but almost any hat will do. I found that when wearing mine, the lowest laser on my forehead was arranged so that I could aim it at things while wearing the hat. For some reason this was ridiculously fun to do.