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 have been mirroring two 1TB hard drives in my PC as a media share for the past several years but my BIOS recently started giving me a S.M.A.R.T. error every time I booted warning me that one of my drives was about to fail. I could have just replaced the faulty drive but decided instead to upgrade to two new 3TB drives and use the old drives as galvanometers for a music-responsive laser projector.
Back in the 90's I came across a device in a music store that was enclosed in a plastic case about half the height of a shoebox that had a mirror connected to a voice coil with a lamp behind a red filter and lens that focused the beam on the mirror so that it produced a red dot that would move to the beat of the music. It wasn't a laser but it worked really well. I don't know what happened to it and can't find it referenced anywhere on the Internet but I decided to recreate it.
I searched the Internet and found several DIY laser projection systems. This one uses old hard drives and a red laser and this one uses hard drives and an Arduino controller to change the color of an RGB laser. I decided to use just a red laser and leave the components exposed.
Step 1: Disassembling the Hard Drives
A mini Torx set greatly helps disassembling a hard drive.
Step 2: Removing the Parking Magnet
You need to remove the "parking" magnet. This just holds the actuator arm when it is not reading or writing any data. Every drive is different but this is what it looks like in a four-year-old Hitachi Deskstar 1TB.
Step 3: Deciding How to Mount the Mirror Bracket
After disassembling the drive, I discovered the actuator arm in this particular model was held onto the hub bearing by a set screw. I found a longer screw at ACE hardware that fit the threads and decided to use this to mount the mirror bracket.
Step 4: Making the Mirror Bracket
I bought a small, thin sheet of aluminum at the hardware store to make the bracket.
Step 5: Mounting the Mirror Bracket
My first bracket was pulled over backward by the force of the centering spring. There was a small hole on the top and to the side of the actuator arm hub so I used one of the screws leftover from disassembly of the hard drives to screw down into the soft aluminum to thread it. I then made another bracket but left a little lip on the end so I could drill a hole through it for the top screw. Those two screws on two different axes were enough to keep the bracket upright.
Step 6: Installing the Centering Spring
You need a spring to keep the actuator arm centered or your laser beam pattern won't stay centered. I cut two slits in the back of the bracket with a Dremel and lifted the center with a small, flat-tip screwdriver to create an attachment point for the spring.
Step 7: The Laser
I bought three different strengths of lasers because I wasn't sure how powerful it needed to be. I wanted it to be bright enough to bounce off two mirrors and still be bright but not so powerful that it would burn things :) I bought a 50mW, 100mW and a 250mW red laser. They are all 12 mm in diameter but the 50mW is a little shorter than the others.
Step 8: Heat Sink and Stand
I bought two different heat sinks. One came with a stand and had a threaded hole in the bottom for screwing it onto the stand but the other one had a fan and mounting hardware which I wanted to keep the laser cool so I bought both. The heat sink didn't come with a set screw to tighten the inserted laser module so I had to order some M3 set screws.
Step 9: Powering the Actuator Arms
At first I bought a DROK 15W+15W Amplifier board but it wasn't powerful enough to move the actuator arms very much. I then bought a SMAKN TPA3116 Amplifier Board which had plenty of power to move the arms at only half volume. The amplifier had a small, SMD blue power led which didn't seem too bright until I started using the fog machine with the laser and then the blue light became distracting so I scraped it off with some cuticle clippers. I bought a Wearnes 3A 12V power supply to power the amplifier. It may seem a little expensive for a power supply but the halogen light in my water fountain kept burning out all the other power supplies I've tried over the years but the Wearnes has been going for five years straight. I also bought a 12V to 5V converter to power the laser. The fan uses 12V. I used an old translucent clipboard to make a template for the base so I wouldn't make a mistake drilling into the $20 piece of aluminum I bought.
Step 10: Connecting the Actuator Arms to the Amplifier
The voice coils of the actuator arms are connected directly to the amplifier's speaker out terminals. One hard drive is connected to the left speaker out and the other one to the right speaker out. You can try to solder the + and - leads to the end of the voice coil's winding wires that usually terminate near the base of the actuator arm but I found it much easier to solder them where the ribbon cable terminates on the underside of the hard drive underneath where the circuit board was. To find the correct contact points, connect your speaker wire to the amplifier, power it up, start playing some music and then touch the ends of the wires to each pair of contacts until you hear the music playing. Solder the wires and then secure them. You can use a drop of hot glue or epoxy but what I did was screw a little plastic strip cut out from the top of a black, Sterilite plastic tote lid in case my solder connection came loose and I needed to re-solder.
Step 11: Making the Aluminum Base
I bought a nice piece of 12" x 12", 0.09" thick 6061 aluminum to use as the base. I chose 6061 aluminum because it cuts a little easier than 5052 aluminum but if you are going to be bending or shaping then use 5052 aluminum because 6061 aluminum can break when bent at sharp angles. The heat sink stand came with a flimsy, metal base so I decided to use a threaded rod connector bolted directly to the aluminum instead.
Step 12: Making the Mounts
I used a piece of aluminum angle bar to make a mount for the power switch and DC power connector and used another longer piece to mount the hard drives.
Step 13: Making the Mirrors
I was going to use regular glass mirrors but gexcube14 explained in the comments section of his video that the problem with glass mirrors is that the laser reflects off both the back of the mirror and the front of the glass so you have two dots. This wiki article explains it. You can salvage first surface mirrors from an old digital projector but since I didn't have any of those lying around I decided to do what he did and make mirrors from the leftover aluminum hard drive platters. They aren't quite as reflective as glass mirrors but you can use a more powerful laser to compensate. I used Scotch double-sided tape to attach them to the brackets but I was worried they would vibrate loose so I used mini cable ties for a little extra security.
Step 14: Finished Product
Here is the finished product. I first installed the 250mW laser but it was so bright that it gave me a headache just watching it reflected off the wall so I stepped down to the 100mW laser and that was just right. I found some small, tapered rubber feet with washer inserts for the feet from Grangeramp.com. I used one up front with a long screw and wingnut so I could adjust the angle of the projector. A majority of songs produce a diagonal, squiggly line because the beat of the music will make both the horizontal and vertical axis jump at the same time hence the diagonal squiggle. If you reverse the polarity of one of the hard drive actuator arms at the speaker terminals, the diagonal shifts 90 degrees. Some songs, particularly progressive, trance and other EDM songs that use a lot of synthesizers can produce some really interesting patterns. What is also interesting is that when I played the song in gexcube14's video, W&W's Sean Tyas D.N.A. remix, the patterns produced by my laser projector were identical to the ones made by his so it's not random; Each song has a unique, visual signature. Thanks for looking and have a great summer!
Step 15: ***UPDATE***
UPDATE: I finally found pictures and even a video of that old device from the 90's that served as the inspiration for these Instructables. It was called 'Laser FX' even though it didn't actually use a laser. Good times.