Will this LCD work w/o a backlight? Educate me on LCD types

Discussion in 'General Electronics Chat' started by spinnaker, Feb 15, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    I need to have a project that will require as low of a power consumption as possible. I want to add am LCD but it will really only be looked at during setup and periodic monitoring. So I don't really need a a back light.

    I could probably drive the LED with PWM and turn it off when not needed but why go through all of the trouble.

    I was looking at this LCD. It has a TN, STN display. Do I really need to hookup that backlight to be able to view the LCD or will it work fine without the light?

    Wht is it listed at both TN and STN?



    Is there a reference that I can go to that talks about the pros and cons of the various types?
     
  2. BMorse

    Senior Member

    Sep 26, 2009
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    check this out >> http://en.wikipedia.org/wiki/Liquid_crystal_display#Twisted_nematic_.28TN.29
    makes for some good bedtime reading.....

    But for the most part, most LCD's can be read without a backlight, but only with some good ambient lighting, with slight tweaking of the contrast.... most also require a separate control for the backlight so adding a switch to turn it on or off would not be a bad thing in case you have to read it in the dark.... if you do purchase an LCD display with backlight, get the LED backlight and not the EL, since an EL backlight requires an inverter to power up correctly....
     
  3. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    Thanks for the link and the tip on the type of backlight. Yeah it looks llike this one is LED.

    The switch is a good idea but maybe I will just go ahead and use PWM. That way no one can forget to shut the switch off. :)
     
  4. BMorse

    Senior Member

    Sep 26, 2009
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    Why not use a 555 for an "Off-delay" timer, so the backlight only comes on for so long before it automatically shuts off, that is how most of my DMM's work, the backlight only stays on for a couple of seconds and then shuts off....
     
  5. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    The project already has a PIC so I might as well use one of the I/O pins.

    I was thinking that I would have to use PWM but not really. You 555 timer suggestion made me think that I can just use the PIC to turn it on or off. Thanks.
     
  6. BMorse

    Senior Member

    Sep 26, 2009
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    I sometimes mod LCD's and add the backlight if they don't come with one.... usually I can get the LCD for cheaper without the backlight and just add my own.... here are some pics of one I modified with some salvaged parts....

    here is the salvaged LED PCB's with 4 Blue LED's each (I had 2 of these boards salvaged from some LCD off of an old Office Phone)

    [​IMG]

    I added the current limiting resistor for each LED right onto the salvaged PCB...

    [​IMG]

    Attached them to each side of the LCD ( I had to modify the LCD itself and add the backlight diffusing material that was cut from a salvaged piece from a laptop screen, which you can see in the pic below the LED PCB...)

    [​IMG]

    and here it is lit up, except my daughters camera doesn't like very bright LED's for some reason and can't take a decent picture with the backlight on showing the displays text...

    [​IMG]
     
  7. BMorse

    Senior Member

    Sep 26, 2009
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    Yeah that would simplify it a bit, just need a suitable transistor to turn on the backlight and just have the pic run the "off" delay.....;)
     
  8. spinnaker

    Thread Starter AAC Fanatic!

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    Would I need a transistor? I light LEDs all the time off the PIC or do those back light LEDs draw a bit more?



    Modding a backlight??? Uou really know how to have fun. :)
     
  9. BMorse

    Senior Member

    Sep 26, 2009
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    some have multiple LEDs that might draw too much current from 1 uc pin, I don't normally connect more than 1 LED per pin on a uc so I use a transistor (2n3904) if driving multiples.

    Also it all depends on the backlights power consumption ;)
     
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