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LED Array

Discussion in 'LEDs and Optoelectronics' started by mctoys, Aug 30, 2011.

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  1. mctoys

    mctoys

    3
    0
    Aug 30, 2011
    Hi All

    I have a probably rather embarrassingly simple circuit question which I would like to ask. I am considering building some LED clusters to use as indicators, side lights and brake lights on my motorbike engined kit car project and would like to test a simple 9 LED array to test the brightness and effectiveness.

    I have based my circuit on using three sets of three LEDs in series using a 220 ohm resistor and 12v supply. I think these values are ok, but I want to build it on veroboard and am unsure whether I need to use one resistor between the voltage and the three series circuits or whether each one needs it's own resistor. I have sketched up a quick diagram of the two options I am considering. The orange strips are resistors, the black strips are connecting wires and the circles are LEDs.

    [​IMG]

    Can anyone give me their advice as to which circuit will work best or if I've completely screwed up!

    Many Thanks
    Dan
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    The 2nd circuit is definitely the way to go (except you don't want to break the 0V strip).
     
  3. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi there mctoys.
    I would use one resistor per 3 led's in series, and calculate the current for three of the led's depending on there current rating and forward voltage for your resistors, others might do it different, any other members do it other than this way ? Dave. :)
     
  4. mctoys

    mctoys

    3
    0
    Aug 30, 2011
    Brilliant, thank you! Yes of course, simple mistake on the drawing!
     
  5. mctoys

    mctoys

    3
    0
    Aug 30, 2011
    Hi Dave

    Yeah, that's what I've got going on with diagram 2. The forward voltage is listed as 1.8-3.2v so I have done my sums based on 2.4v - does that sound sensible to you?

    Thanks
    Dan
     
  6. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Depending on the color (red & orange I guess?), yes, but if you have the LED's in hand it'd be best to test them for Vf at the intended current level(s).
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Yeah, do your calculations based on 2.4V, and then measure the actual current/voltage and make an adjustment as is required.

    You only need a single resistor per string of three LEDs, and whilst you could string more together for the voltage you have, you have chosen a good compromise based on the quite variable voltage you get on a car 12V system.

    There is a sticky thread here which has links to calculators for resistor values which may be of assistance. If you look at that you'll also see verification that your second layout is preferred (and why).
     
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