I’ll be honest – I didn’t take anywhere near enough pictures of this. After the first hour I quickly descended into a geek trance and emerged a few hours later, slightly disheveled and holding a working working laser show but possessing only 13 pictures, many of which were terrible and irrelevant. So I apologize, and I’ve tried to make everything as clear as possible in the instructions themselves.
Power Supply and Control
The first thing we want to do is provide power to the laser itself, and provide any easy method to turn it on and off. The power is coming from the AC/DC adapter, but it ends in one of those plugs we’re all so familiar with. What we need to do is wire a receptacle (which connects to our power adapter plug), to a switch (which allows us to turn power on and off), which then goes to the laser driver board itself.
Cut out appropriate holes for the receptacle (generally a circle) and the switch (generally a rectangle). For the receptacle hole, I used an old soldering iron that I speared into the plastic – feel free to say “THIS… IS… SPARTA!!!” while doing so. For the hole for the switch, I used a Dremel tool and cleaned up the edges with the old soldering iron.
Solder up the receptacle, the switch, and two leads that you will eventually connect to the laser driver board. Use electrical tape to cover up any exposed contacts. It’s up to you to make sure you wire the switch correctly – there’s a ton of different ones out there, make sure to read the specifications. Don’t worry if it doesn’t work, there’s really only one other way to wire it.
Don’t connect anything to the laser yet! Why? We need to mount the switch and the receptacle in the box, and you’ll quickly find that you need to pass the wires through the little hole in order to mount the switch. The laser, needless to say, will have a bit of trouble fitting. Put everything into place, and apply glue to the inside to ensure everything stays put. You don’t need to do this, but it doesn’t really hurt.
Now put on your laser safety goggles. You can take them off if you leave the room to go to the bathroom or something, but trust me, when you look this good, you’re gonna want to leave them on.
Now we can solder those leads to the laser. Be careful that you don’t use excess solder and connect the two power pins to each other! This can always be fixed, but it’s easier to do it right the first time around.
Now fix the laser driver board to a part of the box. I picked the side and set it vertically to leave the most available space, and used a glue gun to mount it since there weren’t any easy screw mounting points. If you look at the board there should be a big piece of metal attached to a component, that’s the heatsink for the power transistor. Make sure it has lots of free space around it, it can get hot and needs to cool off. You can see how I chose to mount everything in the picture at the end of this article.
Don’t worry about mounting the laser itself yet. Make sure the laser is pointing away from you at something non-reflective and cheap (a piece of wood is great), plug the AC/DC adapter in, and turn the switch on. You should see a whitish dot appear. You only see a dot instead of bright green glare because you’re wearing your safety goggles. You are wearing your safety goggles, right?
Alright, now we have a working laser that we can easily turn on and off! Now turn off the switch and remove the power adapter (do both!).
Laser Modulation (or, a little mirror that moves)
Now we need to grab those headphones and take them apart. It’s a lot less complicated than you think. Each set of headphones will be different, just keep taking out screws and gently cutting away plastic until you’re left with the speaker and cord from one side. There should be two wires (or possibly the two wires are covered in plastic so they look like one wire) leading from the cord side into the headband thing. Cut this wire, and use electrical tape to nicely cover the exposed ends of each. I don’t think connecting them is a good idea (drain too much power?), but like I said, electrical engineering is not my specialty. Feel free to comment.
Now you should have one speaker attached to a cord that you can plug into an iPod or a stereo. Plug it in and start playing music to make sure it all works. Now look at the speaker as music is playing – if you’re lucky, it’s nice and exposed, and you can see the speaker cone moving back and forth. If you aren’t, it’s covered in a plastic mesh or similar. Cut it away carefully (I used an old soldering iron again, being very careful not to hit the speaker itself) so you can see the speaker. We want to be able to glue the little circular mirror on the speaker itself.
Grab your glue gun, dab a bit of glue on the back of the mirror, and quickly and carefully place it right in the middle of the speaker, ensuring it remains flat. Don’t get any glue on the mirror itself, and use a tissue to wipe off any fingerprints (or, if you wear glasses, use your cleaning cloth).
Now we want to place the headphone/mirror inside our project box, and align the laser correctly so it bounces off the mirror. I found it easiest to first place the speaker at a 45 degree angle, and fix it in place at one of the box with the glue gun. I also cut a small semicircular notch in the side of the box to give the headphone cable an easy mounting and attachment point in the box.
Ensuring the laser remained parallel to the bottom of the box, I then I adjusted the height of the laser with a mounting made of popsicle sticks. The end result is a beam which bounces off the mirror at a 45 degree angle and then heads straight for the ceiling. This is the easiest way to mount the laser so you don’t need to worry about it hitting your eyes on a regular basis.
Mounting the Diffraction Grating
Now we need to place the diffraction grating so that it intercepts the laser being reflected off the speaker, and breaks it up into hundreds of different beams. We want to place the diffraction grating directly above the mirror if you’ve aligned your laser with a 45 degree reflection angle.
Use a Dremel tool or similar to cut a hole in the top of the project box that’s slightly smaller than the diffraction grating. Then mount the diffraction grating in place with the glue gun.
Final Testing and Assembly
You should now have something that looks somewhat like this.
Don’t worry about that tan circuit board with the LEDs attached the to the diffraction grating, they’re some lights that came with the specific type of headphones I used. I kept them in because they looked kind of cool, not for any technical reason. You don’t need them. Check to make sure that the laser turns on, and that it bounces off the mirror correctly at rest and when music is playing. Then box it all up, and you’re ready to go!
You can see that I’ve added in some ventilation holes above the laser and main power transistor. Do this! The laser will produce heat as part of it’s operation – it’s not normally a big deal, but a sealed box has a way of drastically increasing temperatures.
I hope this helped you – and if you have any questions, just post in comments!