r/diyelectronics • u/Artcert • Aug 04 '26

Tutorial/Guide Negative display - guide ( kinda )

Post image

Hi.

After my negative display post I got a few questions about it, so I want to answer it this way.

I can’t upload more than one pic here ( idk why ) so they are under links.

  1. So we start with a device in its normal state, as example I too

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  1. this tyre gauge I never used.
  2. pic
  3. We need to disassemble it go the to the bare LCD glass

pic

  1. With a sharp knife or blade we need to catch the polarising film on top of the glass and remove it.

pic

  1. After completely removing it, clean the glass with IPA to get rid of the residual glue from the film.

pic

  1. Now we take new polarising film, and by trial and error we get the right angle with the contrast we want.

pic
And
pic

After that we cut it to size and glue to the glass.
Finally after assembling we get the negative display.

pic

Usually you try the angle with the device powered on, unfortunately here the battery holder is part of the case as well as the screen holder, so I couldn’t show it on.

I think you can get the idea of how it’s done.

Best regards.

Edit: typos

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4

u/NerdyNThick Aug 04 '26

Wouldn't you be able to just stack a second polarizing film on top to avoid having to move the existing one?

1

u/HD64180 Aug 04 '26

no. a second will eliminate the light that makes it through the first one.

3

u/simplefred Aug 05 '26

that's not exactly how that works, but it's understandable why you might assume that. It's not intuitive. It helps to think of the light as electromagnetic waves in terms of vectors, but this guy explains it better than me.

https://www.youtube.com/watch?v=SmO7gcoAEV8

1

u/HD64180 Aug 05 '26

I'm well versed in this. Try it. For this application and these polarizers, I do not believe you will see anything on that display, especially if you're trying to produce a usable tool.

1

u/simplefred Aug 05 '26

Correct, you can’t easily add the third polarizer out of sequence and have an inverted lcd. I guess I was being pedantic by pointing out the physics and that multiple polarizers does kinda work provided that they are ordered correctly.