Driving LED backlighting

Discussion in 'The Projects Forum' started by laminaytrap, Mar 27, 2015.

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  1. laminaytrap

    Thread Starter New Member

    Mar 26, 2015
    3
    0
    Ugh... Just closed the tab and lost my draft :(

    Ok from scratch.

    Hi, my name is Jon and this is my first post.

    The Project:
    Motorcycle Gauge (Arduino, Stepper, OLED display, LED backlight, LED indicator lights)

    I have been wanting to build this for some time and I have the necessary skills and resources, but I keep getting overwhelmed when is comes to driving the LEDs for the backlight (and packaging the OLEDs, but that is outside this scope).

    I have a basic understanding of how all these parts work, and have looked at many different solutions, but I am unsure as to which are the simplest/most reliable/or best (if there is such a thing).

    Specifications:
    Supply Voltage= 11 -1 4VDC
    Temp= -5 - 40C
    Speed= -1 - 60m/s :)
    Vibration = Y

    LEDs:
    ~30 @ 3.45V 20mA + (~12 @ 3.45V 20mA or ~12 @ 3.45V 20mA) + (6 @ 2.5-4v 20mA individually switched)

    The 30 White and 12 White sets need to be dimmable (switch or LDR), others probably not.

    I have looked at:
    Purpose built LED drivers (NSI45020 etc.)
    Boost Circuits/Drivers (MC34063A, LT3465 etc.)
    Linear Regulators (LM317etc.)

    I need to figure out what will work well for me in this application. Maybe I should just ignore these fancy chips and use BJTs? I don't know.
    It seems likely that the (30) and (2x12) sets of LEDs will each need one current limiting chip, while the 6 independent LEDs could use another, or individual NSI45020.

    Anyways, I need some guidance here so I can make some good choices/learn about something new and eventually get this project off the ground.

    LED Schematic for reference (quantities subject to change, just for visual on arrangement)
    [​IMG]

    BTW: I have Multisim, Diptrace, and Solidworks. The latter two I am using. I will start using Multisim when I have a better plan of what I'm doing.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,026
    Occasionally, reopening the page will recover at least a portion of what was written. It's not a reliable solution and probably depends on your browser and OS, but it has saved me a few times. It's awfully
    annoying when it fails. For long posts (and your's is close to qualifying), I sometimes use a text editor or save a draft in my e-mail.
     
  3. laminaytrap

    Thread Starter New Member

    Mar 26, 2015
    3
    0
    Thanks wayneh, I tried Ctrl+shift+T but Chrome let me down. I had it open for over a day so it is definitely my fault.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,733
    759
    First you need to find the Vf of one backlite LED that you plan to use.
    You need a variable PSU or a current source to make some measurements.
    After that tell us how many LED's are used for backlite.
     
  5. laminaytrap

    Thread Starter New Member

    Mar 26, 2015
    3
    0
    I don't know what else it is you are looking for. The Vf of the LEDs for the backlight is spec'd at 3.45v measures ~3.3 @ 20mA

    #of LEDs are:
    30, 12 , 1

    Please let me know if you were looking for different information, or if I am not understanding.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,733
    759
    So 3.45V is max Vf or 20mA is maximum brightness ?
    How many LEDs for backlite ?
     
  7. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    Discussions of automotive modifications, and that includes motorcycles, is not allowed according to the terms of service. This thread is closed.
     
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