“Let’s find out how to make a simple enough laser projector out of electronics you can find at home.
There are two ways to create an image with a laser — vector scan and raster scan.
During vector scanning, the laser moves along the outlines of the image, only turning off while moving from one outline to the next. That means that the laser is on most of the time, making for a rather bright resulting image.
That method is most often used in large-scale, industrial laser projectors, but it requires the use of a rather complex electro-mechanical device — the galvanometer — to move the laser quickly. Prices start from $80 a pair and it’s very impractical (though possible) to make at home.
The second method is raster scanning. There, the laser beam moves side to side, drawing the image line by line. That’s the method used in old CRT televisions and monitors.
Since both vertical and horizontal movements are done repeatedly, it requires a much simpler mechanical setup than vector scanning. Also, since the image is divided into separate elements, it’s much easier to program.
The main downside of raster scanning is that the beam goes over every element of the image, even those that don’t need to be illuminated, causing the image to be overall dimmer. But, due the simplicity, that’s the method I chose for my laser projector.
To move the laser beam along a line (horizontally), there’s a very convenient technique: is to use a mirror rotating at a constant velocity. Since rotation is continuous, you can move the beam quite fast. But moving the beam to another line is more difficult.
The easiest option is to use multiple lasers pointed at the rotating mirror. The downside is that the number of lines displayed would be determined by the number of lasers used, which makes the setup more complicated, plus you would need quite a high mirror. But there are upsides as well — the only moving part of the whole system is the mirror (less stuff to break), and using multiple lasers can make the image brighter. Here’s an example of a projector built that way.
Another scanning method, often found on the Internet, is combining vertical and horizontal scans by using a spinning mirror drum, where separate “facets” are placed at different angles to the rotating axis. That mirror configuration makes the laser beam reflect into different vertical angles when the mirror is spinning, creating a vertical scan.
Even though the resulting projector is quite simple in essence (you only need a laser, a mirror with a motor and a synchronization sensor), this method has a big downside — it’s very difficult to build a multi-faceted mirror at home. Usually the slant of the “facets” should be adjusted perfectly during construction, and the level of precision required is insanely high.”