EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: made2hack on March 01, 2021, 01:43:33 pm
-
Hi all,
So this is what I want to do. Shine a light through a 7 segment display so that the segments get projected on a wall. Or the negative of the 7 segments, as the segments would be the dark area blocking the light.
However, I'm not sure what flag or filter to search for on TME or Mouser, etc. Essentially I want a 7 segment or any LCD for that matter that has no reflective backing. Essentially is "transparent" so that another light shines through it.
I can swear I saw this feature before somewhere on my searches but I can't seem to find the search option. Any ideas what transparent or reflective sheet removed LCDs are called?
Thanks in advance,
-
What you are probably looking for is a transmissive LCD : https://newvisiondisplay.com/lcd-modes/ (https://newvisiondisplay.com/lcd-modes/)
The LCD mask used in mask SLA (MSLA) 3D printers might work. For example: https://www.amazon.com/Elegoo-Mars-Replacement-Screen-Printer/dp/B087JB7TZZ (https://www.amazon.com/Elegoo-Mars-Replacement-Screen-Printer/dp/B087JB7TZZ)
With any LCD, you will need polarization to see the image.
-
So for it to work, the polarizing layer has to be maintained?
Thanks
-
So for it to work, the polarizing layer has to be maintained?
The typical transflective LCD has one polarizer on the front, and depends on the rear reflector to transmit polarized light back through the LED and front polarizer again. A transparent LCD would need two polarizers, one front and one on the back. Most LCDs work with circularly polarized light, and the electric field lines up the crystals to interfere with the circular polarization, turning the segment dark.
Jon
-
As Jpanhalt said, what you are looking for is a transmissive-type display.
Most numeric LCD displays are supplied as transflective or reflective devices, so transmissive ones can be somewhat difficult to find. However, you can convert either transflective or reflective displays to transmissive, provided you have the appropriate polarizing film.
Basically, you just remove the transflective/reflective backing by carefully peeling it off the display and then replace it with transparent polarizer. By rotating the polarizer 90 degrees, you can convert it from the standard look of dark segments on a light background to the inverse (light segments on a dark background). I've done this successfully.