Building a laser projector is something that's always been on my list of things to do. Well, maybe not always, but at least since I got my first laser pointer.
The other day I found this awesome web page where someone explains how they built their own laser projector. The basic idea is simple enough, as it's just two galvanometers with positioning feedback in a servo setup.
Still a bit too much for me to build, though. I don't have magnets I can glue to a rod and then grind to a nice round shape, nor do I have the grinder, nor does that even sound like something I'd like to try. ...and that capacitive feedback sensor, I probably wouldn't get that to work either.
So I did this instead:
The mirrors are mounted on two ordinary DC motors, in as much as DC motors with nine rotor contacts and smoother than usual bearings are normal. For positioning feedback, I used infrared interrupter sensors in an analog fashion rather than their typical digital use. The result is that there isn't a whole lot of mirror movement between the full scale of the sensor's ability, but my plan was to use this thing to project onto buildings 100 feet away, and so the fact that it doesn't have a large range of movement actually works well.
At first the thing couldn't hold the motors still, so I processed the feedback signal through a high-pass filter. Then it could hold it still, but it also wouldn't move it when it should, so I connected a potentiometer between the filtered and unfiltered signals so that I could dial in on the best ratio between the two. There's certainly better ways to do that. Probably the way described on the web site above would work well, but I'm too lazy for all that.
Anyway, I then designed a simple "star" pattern to display. Here's a photo of my oscilloscope displaying the pattern:
...and here's what it looks like projected onto the wall using my laser projector:
Considering the half-ass way I went about building it, I'm rather surprised it works even that well.
Here's the same thing with a longer exposure time:
Here's a long exposure in the direction of the laser projector. You can see the cone of laser light coming from the projector and extending out the center-right of the photo:
...and since none of those photos look really cool, here's one I took a few days ago:
For that I just used a 15 second exposure and pointed the laser in every direction I could during the exposure.