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Discussion in 'LEDs and Optoelectronics' started by daddy, Dec 1, 2009.

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  1. daddy

    daddy

    10
    0
    Dec 1, 2009
    hi, am new to leds, but am facinated by the miracles the small light does. ok, actually am doing this as part of a hindu festival in singapore and i wanna do some lighting. could anyone help me? how am i to solder 14 white leds at 3.5V and 20mA & 1 red led at 1.7V and 20mA in a single plain circuit board. can any one draw me a rough pic?
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    You may want to have a look through the thread named "Basic LED Questions" that is close to this one.

    White & blue LED's are the same.

    For 9V you can use two White LED's in series for each resistor. R=(9-(3.5*2))/0.02=100 Ohms.
    Red LED: R=(9-1.7)/0.02=365 Ohms.

    For 12V you can use three white LED's in series for each resistor. R=(12-(3.5*3)/0.02=75 Ohms.
    Red LED: R=(12-1.7)/0.02=515 Ohms.

    But 14 doesn't divide evenly by 3 so:
    If you choose to use two white LED's in series for each resistor on 12V then R=(12-(3.5*2)/0.02=250 Ohms.

    I'm sure you'll find wiring diagrams if you Google.
     
  3. daddy

    daddy

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    Dec 1, 2009
    ok, how abt if i connect them in parallel?
     
  4. daddy

    daddy

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    Dec 1, 2009
    any links whereby they teach how to solder to a circuit board?
     
  5. neon

    neon

    1,325
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    Oct 21, 2006
    know this no LED are created equal blues require mostly more voltage source. green usualy provide greater MCD output per size. know that it takes 20ma to 400ma to light them up depending on size. actualy lemuxes takes more current yet.
    the MCD can be 500 to 250000 mcd. So when you buy must decide what for. a 250000 MCD is defenetly not an indicator but more a light source. WANT TO KNOW MORE?
     
  6. daddy

    daddy

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    Dec 1, 2009
    yup. of course, coz ive got nt much time left.
     
  7. neon

    neon

    1,325
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    Oct 21, 2006
    well national semi has all kinds of $3.00 sources to drive these guys your best bet is to string them in series that makes 50.7 v at 20ma you could just split into 2 series 22v @20ma or better yet just 4 strings about 13v @ 20ma. then get cheap zeners 4 each and use direct from line 120v ac one diode in series with these 4 strings add the limiting resistor of 5.1k [ @ 3w this is wasting power] but simple. no need to add a reverse diode across the leds since the zener will conduct in the reverse direction when negative. any scheme of series leds depends on your chouce.
     
  8. daddy

    daddy

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    Dec 1, 2009
    wow... it sounds gr8. well, will try out this and will letcha know soon ya.
     
  9. daddy

    daddy

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    Dec 1, 2009
    Sorry Rosqueline. forgot to ask u smth, can i use alkaline batteries for the leds? like energizer? if i could, what volt battery can i use for the leds that i asked u ealier? recommend me smth else if u find it useful.
     
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Oh yes, many LED flashlights do, using 3 penlight cells in series for example.
    That low voltage requires parallelling all diodes.
    So for 4.5V you use one resistor for each LED.
    White: R=(4.5V-3.5V)/0.02A=50 Ohms. (You can use 47 Ohms.)
    Red LED: R=(4.5V-1.7V)/0.02A=140 Ohms. (Use 120 or 150 Ohms.)
    Total current draw will be 15*0.02A=0.3A - giving 2Ah/0.3A=6 hours burn time on AA cells.
    Of course the intensity will go gradually down as time passes, but not as badly as bulbs do.
     
  11. daddy

    daddy

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    Dec 1, 2009
    Thank u so much Resqueline, will letcha know the results. :)
     
  12. daddy

    daddy

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    Dec 1, 2009
    you mean, i can parallel all the whites and the single red leds together and run on AA cells? that's great. but, does the red one need an additional wiring or i can parallel them as well?
     
  13. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Each LED needs its own resistor, and each LED+resistor is to be parallelled - i.e. all running on 4.5V.
     
  14. daddy

    daddy

    10
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    Dec 1, 2009
    thank you so much Resqueline. coz of you ive done a gr8 job.
    thank u so much for helping me. in future, if i have any doubts its only u can clear for me.
     
  15. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    You're welcome. I'm glad whenever I'm able to help someone.
     
  16. daddy

    daddy

    10
    0
    Dec 1, 2009
    will post my project in facebook after the whole thing is over. pls do take a look. thank u so much once again.
     
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