WS2812 8x8 projector

A projector using a clear resin printed lens array as well as a cheap fresnel magnifier lens for projecting a 8x8 WS2812 LED-matrix on walls and ceilings.

Background

This is the result to two differnt ideas on how one could project a LED matrix: My idea was emulating LED flashlight optics and have a small biconvex lens in front of every LED, making each a “spotlight”. Bilian had the idea to use a single large fresnel lens to project all of the matrix at once.

Turns out you need to combine both approaches to get the best result:

On its own the resin printed array is highly depended on alignment of the LED as even a small misalignment is amplified when projected. Because of this and the physical separation of the red green and blue diodes on a ws2812 chip you only project a blurry blob when only having the resin printed lens array.

Using only a fresnel magnifier lens already works well even on its own, but as it is projecting an exact image of the matrix, each LED point source is also projected as a tiny bright point of light, with seperations between the red, green and blue emitters clearly visible.

Having the lens matrix collect the light results in a much better projection when combining it with the fresnel lens: In the following comparison the first 3 rows are directly projected using only the fresnel lens, the rows below are projected with both the fresnel lens as well as the lens array: 

Without the lens matrix one can see each color emitter, in real life the projection appears more even and brighter in total when the resin printed lens matrix is added.

Fabrication

Specialized hardware needed:

• noname 8x8 ws2812 matrix from AliExpress + microcontroller (for example some ESP board with WLED)
• G217 clear resin or a similar clear resin
• fresnel magnifier from ebay (search “fresnel magnifier” and you most likely get the same 18cm x 12cm magnifier I used)
• when laser cutting the parts for the projector: 3mm acrylic; ~two sheets of 400x300mm
• 4x 12mm M3 screws and 4x M3 nuts

The resin lens array should be printed upright, personally I have the following process to get a good clear result as shown below:

1.  Print the lens with supports perfectly upright but at a 22,5° angle on the Z-axis, this avoids pixel stair-steps in the center of the lenses. Manual supports on the sides of the lens were added.
2. After the print: let most resin drip off but do not wash part: move the resin covered print around to have equal coverage on the whole part. A hand operated dust blower (like the one from iFixit) helps to gently equalize the resin
3. Cure the part for 2 minutes in an UV curing chamber, remove supports.
4. Take the print and cure it in a clear container submerged with distilled water for another minute. In this step the lens gets slightly cloudy: clean afterwards with IPA
5. cure the part again for a couple of a couple of minutes, curing too long will let the part go slightly yellow. Clean again afterwards with fresh IPA

The frame of the projector is meant to be lasercut, all other parts can be printed using a FDM printer, make sure to print the correct multiples as given in the file name.

There are two spacers for the resin lens: a basic 8mm x 8mm raster and one for the more commen 8.1mm x 8.33mm matrix raster of cheap ws2812 led matrix panels.

The lasercut frames for the fresnel magnifier are held together with the 3d printed clamps, the “fresnel bracket” allows the rotation and sliding of the fresnel lens to achieve proper sharpness even when projected on angled surfaces.

The lasercut chassis is slotted together and then clamped together with the M3 screws.

For now the whole LED and resin optics assembly is mounted using clear or double sided tape.

If you want to 3D print the projector frame: The provided step file contains solids for all the parts, you can use for example Prusa slicer to extract the individual models using the rightclick “split” “to objects” function.