Texas Instruments developed digital mirror devices, and the subsequent digital light processing (DLP) projector, starting in the late 1980s. The technology is a wondrous and fanciful application of micro-scale electronics and optics. Most of us that have tangled with these devices have had to learn their mode of operation from diagrams and our own imagination. But what if you just built one at a large enough scale that you could see how it worked? Well, [jbumstead] did just that!
A real Digital Micromirror Device (DMD) consists of hundreds of thousands of mirrors, which would be impractical to recreate. This build settles for a simpler 5×5 array made using half-inch square mirrors. It uses solenoids to move each individual mirror between a flat and angled position to create the display. The solenoids are all under the command of an Arduino Mega which controls the overall state of the display and shows various patterns.
It’s not perfect, with the mirrors not quite matching in angles at all times, but it demonstrates the concept perfectly well. When you see it in action with light bouncing off it, you can easily understand how this could be used to make a display of many thousands of pixels in a projector arrangement. We’ve featured some other DLP hacks before, too, so dive in if you’re interested.
Before TI used square mirrors pivoted on two opposite corners they used a different technology. The mirrors were little metal dimples which popped between concave and convex just like the silicon rubber fidget toys. I don’t know why they abandoned this approach.
Do you think maybe they had problems with metal fatigue with the tiny dimples switching so often?
Maybe due to fragility? That sounds like something that would break after thousands of operations… which, for a projector pixel, would be quite soon.
The dimple will have more dispersion than the mirror, making contrast ratios poorer and requiring a more intense light source to achieve the same output brightness.
I think the solution to better alignment would be to have a frame each mirror is pressed into from behind in the ‘on’ state, then pulled away from on one edge in the ‘off” state. This could be combined with a sprung pivot on the back of the mirror: pull it away from the frame and it will pivot away, push it into the frame and the mirror will straighten out against the tension.