Laser Projector

This ends up being a dot-matrix display.

I'm not sure the best design, but the core idea is good. We're not placing a dot at a specific point in space, we're placing it at a 2D radial point. This could be done with two mirrors on shafts connected to steppers. They would move to position the dot. Of course, then we'd only be using a small range of the steppers motion, so better might be servos, or gear reduction.

But, by going to a dot matrix, we take the whole control aspect out of it. We control when the light is on. Here's the creative bit - we just have two shafts with either 3 mirrors or a prism. Both are spinning fast, but at rates that are relatively prime. Speed becomes an important factor - if we do something like 1024x768, we need almost 1MHz just to refresh the display.

Is this feasible? Let's try some math:

Say we have a grid that is 5x3 and we move 1x1, that works. Let's say we wanted to draw at 60hz. The faster shaft is spinning at 5/3 the rate of the slower shaft, and it needs to rotate 5 times in one frame. But if there are 4 mirrors, then it only needs to rotate 1.25x per frame or 75hz, 4500rpm

Ok, so lets go to 1023x1024. They are relative primes. We need to draw 1024 lines per frame. If there are 6 mirrors (that should be feasible) it needs to rotate at 10240hz, or 614,400rpm. Nope, looks like 20,000rpm is the max we're reasonably going to get.

So 20krmp, lets drop to 40hz and stick with 6 mirrors, that gets us 50 lines, only 7 character lines.

It might be possible to pick up the difference with more lasers - probably divide it into quadrants, which puts using the 100x100 range.

-- Speed Control --

I can put either another laser or just an LED on the back side and pick it up with a phtotransistor. That should let me control the speed.