Brooke Chalmers
u/breqdev
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There's really not much going on with the PWM signals -- they just go straight from an EPS32 GPIO into the DIM pin of the OC5211 chip that's on the driver board that came with the RGB lasers. I'm honestly surprised it works as well as it does. My guess is that there's some smoothing that happens either in that chip or intrinsic to the diode itself that causes it to take longer to turn on and off.
It's definitely not perfect, the green diode specifically will show up as choppy sometimes depending on scan speed. That said, anything I could find with an analog modulation input would have totally blown up the cost of the project.
The PWM frequency is 24 kHz, which I think is the most I can get using the APBClk with 8-bit precision. I might mess around with running at lower precision for a faster output frequency and see if it improves things.
I used boards made by PCBWay -- they sponsored this project and gave me free boards, but the cost would have been about $50 for 5 if I had bought them myself. I used lead free HASL (gold isn't really necessary for the package sizes I used or reliability I want, but I like avoiding working with lead if I can!)
The cost in this case is mostly driven by the board size (200mm wide to fit all of the I/O) -- if your board is 100x100mm it's much cheaper not just from PCBWay but I think from other vendors typically as well.
PCBWay (and I think some of the other vendors like JLC) also have plugins for KiCAD that let you import their tolerance rules for DRC and then order boards with one button click to create and ZIP gerbers in the right format and then upload them to their online quote tool. It's much easier than the error-prone process of generating the gerbers and drill file yourself!
There are commercially available options for this more for professional use, usually for $1000-$2000. Unity is a brand I've heard of a lot (https://pangolin.com/products/raw-1-7-dmx-ilda is their base model), but you can probably find more options by searching "laser show projector" and I think there are some cheaper ones out there too. You might also need a computer to run them or software to put patterns you want onto an SD card depending on the projector.
Note that to use it professionally there are a few more legal hoops to jump through. In the US you need to register the laser with your state, take a laser safety officer (LSO) course, and file a "variance" with the FDA for any shows done commercially. There are more rules you need to follow too that I'm probably ill-equipped to articulate (I think in most jurisdictions beams must be 2 meters horizontally or 3 meters vertically separated from any floor someone might stand on).
Best of luck with finding a system that works for you -- it's definitely not as straightforward to get into as you might hope, but I think the effects you can get are worth it!
The speed really depends on what you're drawing and how large of an image you're making -- text has a lot less tolerance for sloppy motion that SVG graphics usually do, for instance. With the simpler fonts I can do about 20-25 characters usually. The map example image in the writeup is about as complex you can get with it still looking decent to the naked eye. Being in a dark room helps with the persistence of vision effect too.
I'm not sure if you could pull from the 15V rails! I thought about it but the power supply didn't clearly list its specs and I wasn't sure what the current consumption of the laser diodes would be (since they're on the 12V rail too). The Mean Well module I used to get the 12V was cheap and simple enough that I figured it was the safer option.
It's pretty hard to get video that looks good because the shutter speed has to be synchronized to the path drawing, and I just have my phone and not a professional camera, so I didn't take a ton of videos unfortunately -- they just end up looking way more flickery than real life. There's one video of the oscilloscope music demo if you visit the link in the post but that's it, sorry!
