The LCD used for printing on Elegoo Mars is RGB – there are three subpixels – red, green and blue. Since the backlight LED produces a quite narrow range of wavelengths (peaking around 405nm), only the blue filter passes the light. That means that 2/3 of the backlight power is wasted to the LCD. Also, it means that only 1/3 of the pixel is exposed and the rest is hardened only via exposure bleeding – the effect we, on one hand, want to eliminate, on the other hand, it is essential for properly working screen. After my modification, which removed the protective glass, you can see on my prints under a microscope the effect I mentioned – 1/3 of the voxel is nice and sharp, the remaining 2/3 are smudgy.
There were recently announced printers with monochromatic LCD. They feature low exposure times (around 2 seconds) with less power than Elegoo Mars. However, their LCDs have poor resolution.
So I was wondering – would it be possible to turn Elegoo Mars LCD to a monochromatic one?
The LCD stack up
First, I examined the LCD. I figured out that the two most outer layers are the polarizer. They are not glued, they hold similarly like to protective glass. Then there is a bottom plastic film with the pixel electrodes (I am sorry for not providing pictures, however, I was not able to take them from the microscope). Then there is a glass layer – on one side (the top side) it is covered by ITO – a conductive clear coating. On the bottom side, there is a layer of color filters. Between the glass and plastic film is a layer of liquid crystals, more specifically between the plastic film and the filters.
One important part – the ITO layer is connected to the plastic film via a conductive ink – see photo below.
Having experiences with disassembling LCDs before, I know how to separate the glass from the plastic film. Just use a fresh Xacto knife and slide it between the layers, move along the perimeter and the layers separate:
You can nicely see the liquid crystal. I used a rubber spatula to save as many crystals as possible from the glass. Then, I started to scratching of the filters. It was pretty easy using a knife. I decided to leave the black border – it probably provides correct spacing between the layers – but I am not sure.
You can see that the glass got much more transparent. Then I cleaned it properly and put the LCD back together. Unfortunately, I was not careful enough and I got some dust particles to the crystals. Therefore, I got polarizing patterns on the LCD:
I connected the LCD to mars and run an exposure test. To my surprise, the LCD was working – you can clearly see the test pattern:
So – it is possible to do! To fix the issue, I separated the layers again, cleaned them both with IPA using a paper towel, put liquid crystals I harvested from an old computer screen between them. I got LCD without dust particles, but with strange, colorful, patterns:
Unfortunately, the LCD stopped working. I have no idea why, just a few theories:
- there are different type of crystals and they are not compatible,
- by cleaning the LCD with IPA and paper towel I corrupted the pixel electrodes,
- or I destroyed micro scratches in the surface – see the video by Applied Science about the scratches
- or something else.
Also, I don’t know what caused the colorful effects after using the crystals from a big LCD. Do you have any ideas? Please, leave a comment.
To do more experiments, I am looking for screen donors – I look for people willing to send me their LCDs with dead pixels. Doing these experiments on brand new displays seems to be wasteful to me. So if you have such a display and you live in Europe, please contact me!