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Only one LEDs light up

Discussion in 'LEDs and Optoelectronics' started by MrRobot, Mar 18, 2013.

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  1. MrRobot


    Mar 18, 2013
    Hi, I am a newbie to electronics and something is happening in my circuit that I don't understand. I have an array of 3 LEDs but only one of them lights up(the middle one), although the others are functional, I know this because when I substitute the one that is lighting up with the one that is not that one lights up instead, so it seems to be the position rather than the particular LED.

    Voltage is being distributed through a transistor, and some resistors, is it a case of not enough current getting through?
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Are the three in parallel, or in series?

    Do you have a resistor (or something else) to limit the current through them?

    Are they all the same colour?

    Are you doing this on a breadboard?

    Can you post a circuit diagram or even a photo of your breadboard?
  3. MrRobot


    Mar 18, 2013
    Hopefully these pictures will explain my problem.

    photo (1).jpg
  4. BobK


    Jan 5, 2010
    I assume you are talking about the 3 green LEDs. The two outer ones have their 2 leads connected together, so, of course, they will not light up!

  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Understand how a breaedboard like this works:
    Look at this picture.
    As it is shown there, within one row the pins are connected from
    A1...E1 and also F1...J1
    A2...E2 and also F2...J2

    Compare this with your setup: The left and right green LED are short circuited by the breadboard and therefore cannot light.
    You need to put the pins of the LEDs into different rows. For example:
    Anode 1 = A1, Cathode 1 = A2
    Anode 2 = C2, Cathode 2 = C3 /' I used C to leave some space for the LEDs */
    Anode 3 = A3, Cathode 3 = A4

    Now if you add the plus of your source to anywhere in row 1 and the minus anywhere in row 4, all LEDs will light up. Don't forget the current limiting resistor.
  6. MrRobot


    Mar 18, 2013
    Thanks guys. :)
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