I previously published an Instructable that described how to use computer hard drives to make a music laser light show. I decided to make a compact version using an electrical box and RC car motors. I am selling it on eBay: http://www.ebay.com/itm/-/322444469317
Before I begin I should probably tell you that lasers are not good for your eyes. Don't let a laser beam bouncing off of an uncontrolled mirror hit you in the eye. If you don't believe it can happen then read this: http://laserpointerforums.com/f53/hit-eye-1000mw-445nm-blue-laser-69469.html
I made a couple of sample videos. The first one features deadmau5.
For the second one I decided to go old school since when I was growing up I always associated music and lasers with Pink Floyd ;)
Steel Electrical Box (with 3/4" and 1" knockouts on each side)
On/Off Safety Key Switch (the prototype pictured just had a toggle switch)
The first step is to drill holes in the back of the electrical box for the On/Off key switch, DC power jack and the amplifier's 3.5 mm audio input and gain control.
The next step is to drill a hole in the side of the threads of the conduit fitting for the screw that will anchor the rubber band that keeps the mirrors centered.
Next I installed the On/Off switch, DC power jack and the conduit fittings that house the motors and laser.
Next I soldered in the 12V to 5V converter that powers the laser. The amplifier runs off 12V while the laser uses 5V.
Next I used an angle grinder holder to cut notches in the motor shaft couplers to hold the mirrors.
Next I disassembled a hard drive to extract the highly polished aluminum platters to use for the mirrors. If you use glass mirrors then the laser will reflect off both the surface of the glass and the silver backing so you will wind up with two dots. This wiki article explains it. The other advantage of using the aluminum platters is that they can be clamped tightly inside the notched shaft couplers without breaking. If you buy non-working hard drives on eBay to harvest their platters, be sure to visit the HDD Platter Capacity Database to research the model number of the hard drive you are buying to make sure it contains more than one platter to get the most for your money. An older 250 GB hard drive may contain 3 or 4 platters while a newer 1 TB model may have only one.
Next I made a table saw sled to cut the aluminum platters. I used a band saw for my previous laser project but the table saw made much cleaner and and straighter cuts. I briefly experimented with a 100-tooth table saw blade specifically made for cutting aluminum but my regular Dewalt 60-tooth crosscutting blade actually worked better. The trick is to set the blade at the highest attack angle and use toggle clamps.
WARNING: If you are going to be cutting metal with a table saw then you have to take even greater precautions. GO SLOW. Don't clamp both sides of the metal; Just one side or the saw will bind and throw the blade, teeth or metal at you and kill you. Don't attach a shop vac to the dust outlet when cutting metal because it can start a fire in the canister. Wear an apron or overalls and a full face shield, not just safety glasses, because those hot metal shavings flying at you can hurt.
The next step was to install the amplifier. It had a very bright blue power LED that I was tempted to cut off so it wouldn't compete with the laser in a dark room but the way the amplifier is oriented the heat sink blocks it from direct view and makes it reflect a diffuse blue color inside the electrical box that gives it a really cool look.
Next I installed the shaft couplers on the motors and inserted the mirrors into the notches and tightened the set screws. I replaced one of the set screws with a longer screw to hold the rubber band. Then I inserted the motors into the conduit fittings.
I soldered the speaker wires to the motors on my first prototype but later switched to 2.8 mm female spade connectors after I accidentally burned out one of the motors by applying too much heat with the soldering iron. An advantage to using the spade connectors is that you can disconnect the lower motor so the laser only moves in a horizontal direction creating the liquid sky effect. I connected the right channel to the top motor and the left channel to the bottom motor but it really doesn't matter. It doesn't even matter which motor terminals the negative and positive leads attach as long as both are connected.
Then I installed the laser module. It just clamps inside the 3/8 in. cable clamp adapter. The neat thing about the clamp is that you can easily remove the laser and swap a different colored laser pointer.
Here is how everything is wired up. The rectifier diode was only needed for the blue and green laser modules. They were getting shorted when their metal housings were grounded to the electrical box so I isolated the ground of the 12V to 5V DC-DC step down converter with a 1000V 3A rectifier diode and that did the trick.
Then I fired it up to test with a little fog from this fog machine. Watching the laser pattern is cool by itself but adding fog takes it to another level. With it you can see the actual laser beam as it cuts through the air. The best thing about using the conduit fittings to house the galvanometers is that everything is easily adjustable. Once the top fitting has been adjusted so the laser beam is reflecting off the center of the lower mirror it can be tightened and left alone but leave the lower fitting just finger tight so you can twist it to move the laser pattern up and down the wall or even onto the ceiling without physically tilting the box. The sharp teeth of the steel locknuts that came with the fittings would dig into the steel so much that they would self tighten to the point where it was impossible to loosen without tools so I replaced them with 3/4" PVC locknuts. The biggest advantage of using the motors over the hard drives, besides size, is that they allow for much greater mirror travel so you get a much wider pattern at closer distances.
For the finishing touch I cut the corner out of the steel cover plate to make a window for the laser when it is installed. Leaving it off allows you to throw a slightly wider pattern and also project onto the ceiling. Again the table saw worked great for cutting metal.
WARNING: Again, if you are going to be cutting metal with a table saw then you have to take even greater precautions. GO SLOW. Don't clamp both sides of the metal; Just one side or the saw will bind and throw the blade, teeth or metal at you and kill you. Don't attach a shop vac to the dust outlet when cutting metal because it can start a fire in the canister. Wear an apron or overalls and a full face shield, not just safety glasses, because those hot metal shavings flying at you can hurt.
Here's another video that shows how it handles a variety of songs. It really allows you to "see" your music. It is also simple to use: You plug your audio source into the 3.5 mm audio jack, plug in the power supply, turn on the power, start playing music and adjust the gain control to adjust the size of the laser pattern. After I showed it to my family and friends they all wanted one so I made several using various colored lasers and decided to sell them on eBay: http://www.ebay.com/itm/-/322444469317 It comes with everything: The box, power supply, audio and power extension cables and audio splitter. Thanks for looking!