Analog Laser Projector
I've been interested in lasers for a long time,  and recently they have become so ubiquitous that a laser that would have cost thousands of dollars is now just a few hundred dollars.  The time was right, I decided, to build my laser projector.

Most of the laser light shows that you see these days are computer controlled, with pre-programmed patterns synchronized to the music.  I wanted to make something that was analog, reacting directly to the music, whatever music was playing.  The first two lasers I used were both pulled from some graphics equipment, one helium-neon (red, 632.8nm), and one argon (blue, 488nm). both about 20mW. The head of the argon laser is about the size of a shoebox, the neon laser head is about the size of a policeman's flashlight. I mounted the neon laser in some aluiminum blocks that are typical for adjustably mounting cylindrical things in industrial plants.

de-coned speaker To make the lasers dance, I got a bunch of identical powered PC speakers, and removed the speaker cones, replacing them with small pieces of front-surface mirrors.  Silicone turned out to be a good material to use to glue the mirrors to the speakers. Of course they aren't much use as speakers any more, but that's OK; they're just running off of the line output of my stereo; other speakers will provide the sound for people to hear.

trial Overture to Tommy Just dummying the setup on a table, I learned that just how the chip of mirror was glued to the speaker made a big difference in how much the laser bounced. After cannibalizing about six speakers I had two that satisfied me.  It turns out that low notes make the lasers move around the most; high notes just make little jiggles.  More on that later.

speaker mounts laser mounts Next, I needed to make some kind of way to mount all this stuff, obviously, I couldn't keep on balancing everything on top of videotapes and bottle caps.  My trial setups showed that I needed about 3'x5' to get the spread I needed. I know that you're supposed to do this kind of thing on a solid aluminum optical bench, but I was raised by wolves, so I just used a piece of laminated wood from Home Depot.

overview overview For mounting, I used all-thread, some aluminum box channel, and some hardware that's normally used for clamping things to steel beams. In various combinations that got me all the degrees of motion I needed.

house Now I was ready to take it outdoors.  The projection screen is the side of the house.  Since this is a private venue, I didn't need to comply with the FDA rules on laser shows, but I figured it would be a good idea anyway.  So I needed a way to get the beam twelve feet above the ground.  Some construction scaffolding did the trick.

platform from 2nd floor The audio equipment (the stereo from my bedroom) went on the lower level, along with a power strip so I could turn things on and off without climbing up and down. Getting the lasers up to the top took two people. The power draw on the whole setup is about 30 amps, so I needed a dedicated outlet and a 10-gauge extension cord.

show When the darkness was sufficient, you could see the lasers dancing on the side of the house.  Unfortunately, I don't have the equipment to photograph that very well, but here are a few pictures.  In real life it's much more impressive. The sequences are at 1/60 of a second, but the human eye percieves a brighter pattern that's constantly in motion.

IMPORTANT! If you want to try this yourself, please familiarize yourself with laser safety first. A good place to start is the FDA's Center for Devices and Radiological Health.
Future projects:  As it stands, the the red laser is one channel of the stereo signal, and the blue laser is the other. The next step will be to combine the stereo signals to mono, and by using a speaker crossover and an octave divider, so that the red laser dances to Jack Bruce while the blue laser dances to Eric Clapton. It would sound terrible, except that the mirrored speakers make virtually no sound; you'll still just hear the sound of the main speakers. (Thanks to Rik Elswit of Bananas at Large, an SF Bay area music store, for technical help on how to implement that.).  

Lasers have also gotten smaller and cheaper since I started this project; the next version will use DPSS lasers, which will knock about a hundred pounds off of the total weight.

All text and images © 2004 by Alan R. Turner.

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