Electronics > Manufacturing & Assembly

Choosing a filter for a 7 segment LED display

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e100:
I bought some cheap green LED 7 segment voltmeters from ebay and they came without a front filter so under normal lighting you can see the non-illuminated segments which results in poor contrast.

I went looking for some green transparent plastic thinking that this would be a common item for displays but apparently not. I tried the lens from a pair of sunglasses and that looked OK, so I went looking for neutral grey transparent plastic which lead me to ND2, ND4 and ND8 filters designed for photography.

I've never seen these filters in person and it's difficult to tell from the photos which of these would be roughly equivalent to the lens in a pair of sunglasses. Can anyone suggest which density grade is likely to give best results? 

ar__systems:
Why don't you just try? Get transparent film for laser printer, print few samples at different densities, and choose the one you like.

sokoloff:
Another thread with some pics of window tint film (including light transmission percentages):
https://www.eevblog.com/forum/projects/aesthetics-led-bar-graph-in-aluminium-panel/msg1210023/#msg1210023

e100:

--- Quote from: sokoloff on July 16, 2018, 01:22:18 pm ---Another thread with some pics of window tint film (including light transmission percentages):
https://www.eevblog.com/forum/projects/aesthetics-led-bar-graph-in-aluminium-panel/msg1210023/#msg1210023

--- End quote ---

After some more research it seems that regular sunglasses have a transmittance of about 25% (optical density of 0.6), therefore a ND4 filter should do the job.

David Hess:
Art supply stores carry acetate or Mylar (polyester) colored film in different colors.

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