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Thread: Sooo, I need to replace the LED's on my Lilliput EBY701-NP/C/T

  1. #1
    Constant Bitrate
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    Sooo, I need to replace the LED's on my Lilliput EBY701-NP/C/T

    I've found suitable replacements at DigiKey but what color should I get?
    Cool white, neutral white or warm white?

    I'm thinking warm would be too...well, warm and yellow. So it's down to neutral or cool.

    There are 27 LED's along the bottom and DigiKey has them for $.90 each. $25 for just enough, plus some extras...I'd like to keep the cost under $30 so I don't want to order both colors.

    Any suggestions?
    Thanks,
    davidk

    p.s. If anyone has a dead monitor that has working LED's for under $30 I might go that route.


    DigiKey part numbers I think will work if your interested.
    492-1278-1-nd
    492-1279-1-nd
    492-1281-1-nd

  2. #2
    MySQL Error soundman98's Avatar
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    are you sure they are plcc2's? while i haven't opened a screen, i guess i thought they were smaller..

    5000k is the whitest white you can get without a tinge of blue(higher) or yellow(lower) in the kelvin spectrum(i ordered some of every color temp around it to confirm).

    personally, i have started using these for the white portions of my hvac conversion, though i believe the blue led's i'm using are bivar brand..:
    425-2749-1-ND

  3. #3
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    Thanks for the reply,
    Not knowing much about how surface mount stuff is categorised and from what DigiKey had in-stock those were the best fit.

    I've already taken apart the display and the LED's are 2.8 x 1.4 x .8mm They're soldered to a small strip which is stuck to the light pipe. They're side emitting.
    I didn't see any identifiers on them so I'm just going by size.

    Only some have burnt out so the thing is back in the car till I get replacements. Lest anyone worry about their display burning out, I'm driving my LED's separate from the display using a PIC.
    I guess I didn't do a good enough job measuring the voltage and current provided by the display when I made my driver.
    There are 27 LED's. I'd bet their broken into 9 groups of 3. The typical forward voltage is 3.2volts so three in series would take 9.6volts. Four in series would require 12+ volts and doesn't go into 27 evenly.
    When I get to doing this I'll trace out how they've got them wired. I'm sure it will work, but if I need to I'll make up my own circuit board.

    Thanks again,
    davidk

  4. #4
    MySQL Error soundman98's Avatar
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    well, with that info, it looks like your middle and last link should be the closest related candidates.. i also have some of those in my parts bin, and those are really tiny!!

  5. #5
    Maximum Bitrate tft_lcd_org's Avatar
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    I have a high bright LED rail from a 669 that will fit your 701's LCD if you want it.
    New part, pulled as a complete assembly from a cracked LCD.

    I will ship you the whole thing.
    PM me

  6. #6
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    I know this is for the 629 but It is probably similar: http://www.lilliputuk.com/uploads/at.../629GL_LCD.pdf

    There are 9 groups of 3 leds. voltage drop of about 9.5v and want around 180ma. I measured mine at 189 stock so I think they tend to over drive them. I'm using 12v regulated power supply with a 12ohm 1 watt resistor and I'm getting about 180 - 184ma. What were you feeding your backlight?

    Check with Duayn from Motor City. He can get you the LED's you need. Also, MOCOSO has some parts laying around. Both of these individuals offered substantial deals on just the backlight portion.

  7. #7
    Constant Bitrate
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    Thanks guys,
    That's some good info.

    I'll have to go back and calculate what I was driving them at. I bet they were over driven.
    I'm looking for a circuit that will provide better regulated power this time. Constant current is what you want for LED's, right?
    An LM317 can make an easy constant current regulator but I've read it's not very stable with temp changes. Don't know how big a concern it would be.
    I could also use a buck-boost regulator to provide stable voltage to the 317. Would that make sense?

    Thanks for any suggestions,
    davidk

  8. #8
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    Yes, constant current is best for LED's. They will work fine without constant current so long as you don't over drive them all the time. Like I said, I did constant voltage... Your best bet might be a Buck controller of some type for constant current. I'm not sure those typically let you PWM them though depending on what you are doing with your PIC. I know the Buck Puck I have from an old project doesn't. It does have a reference line for dimming but PICS usually don't have analog outs I don't think.

    It is possible that if you feed them 9.5v or slightly under you would be golden. Being that I'm not a sparky, I'm not gutsy enough to try that.

    I would be very interested in what you were driving them at... just a sanity check for what I'm about to install.

  9. #9
    Constant Bitrate
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    I've been doing a little more searching and I think I've come up with a better alternative.
    Instead of making things harder (like I usually do) why not use something that someone smarter already came up with.
    LED driver chips will do just what I need. They even allow the PWM signal from my light sensor to drive them.
    The ones I found that require the fewest external components are:
    CAT4101 - http://search.digikey.com/us/en/prod...5CT-ND/1933886
    STCS1a - http://search.digikey.com/us/en/prod...6-1-ND/1880294

    The second one doesn't need a separate 5volt supply, but the first has a handy chart for the current setting resistor.
    Since I've already got 5volts for the PIC the first one might be my choice.

  10. #10
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    Nice, I like that. I might redesign my circuit around one of those as I'm still in the building stage. Did you find any through hole? I didn't etch a board and would rather not.

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