How is a segment illuminated in a typical 7-segment display?

Discussion in 'General Electronics Chat' started by kgstewar, Feb 1, 2016.

  1. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Consider a common 7-segment display, like this one. I noticed in the datasheet schematic, they show one LED per segment, which may just be schematic, although for a larger display they show 3 LEDs per segment, so maybe they are showing the actual number of LEDs per segment. In any case, here is my question:

    How is a display segment in a 7-segment display constructed such that one LED can uniformly illuminate the entire segment?

    I have tried to make my own LED segment by putting an LED behind some partially translucent white acrylic. I always get a fairly localized bright spot and not the uniform illumination that you get in a 7-segment display. Maybe I just need to line up more LEDs for each segment? Or is there a trick?

    thanks,

    Kevin
     
  2. hp1729

    Well-Known Member

    Nov 23, 2015
    1,946
    219
    I think all possibilities are apparent. Consult the data sheet for the display you are considering.
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
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    The cavity the LED is in is filled with a material that diffuses the light emitted by the LED. The surfaces of the cavity are also reflective.
    Your results will never be as good as a display that considers angles of reflection and the interface between the LED package and your difusing medium.
     
  4. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Thanks, any idea what the material is that they use to diffuse the light emitted by the LED? Maybe an epoxy with a characteristic refractive index? I'm happy to experiment.

    I'm trying to make displays with unconventional shapes (perfect circle transected by 2 lines, for example).

    thanks!
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
    3,242
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    It's a glass filled epoxy resin with the color chosen chosen for optimal optical transmission based on the wavelength of the LED die in question.
    You might check with a company like VCC that sells light pipes to get some ideas. I've seen light pipes used in a lot of equipment. Sometimes they shape/difuse the light from a discrete LED; other times they bend the light 90 degrees.

    You might also opt for a panel in front of the LED with a cutout in the shape you desire.
     
  6. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    I was doing some googling and ran across this product (and a few others). Seems like it may be effective at diffusing the light from individual LEDs so that I might be able to create my own more-or-less uniformly backlit LED displays. I'll give it a try and report back.
     
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