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Some LEDs Not Lighting

Discussion in 'LEDs and Optoelectronics' started by Sloan5556, Mar 8, 2015.

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  1. Sloan5556

    Sloan5556

    10
    3
    Mar 8, 2015
    Hello
    I am just getting into electronics and am doing projects with a breadboard and some LEDs. I got every thing set up for a simple "how to use an LED" project. I put the first LED in the board (with a 560 ohm resister) and it lit up. I put the second one in the same rows ( #? and #?) in line with the first and the first LED shut off. I switch the two and the first one always went out and the second one stayed on.
    Then a couple of days ago I did a 555 timer project. I put the first LED in and it worked, I put the second one and they both worked then I put a third one in and it didn't come on.
    So am I not understanding how a breadboard works or is it some thing else?
     
  2. davenn

    davenn Moderator

    13,865
    1,956
    Sep 5, 2009
    hi there
    welcome to EP ;)

    show us your circuit diagram and a photo of your construction and lets see if we can see where you have gone wrong.
    On the circuit diagram, make sure component values and battery voltage etc is clearly shown

    cheers
    Dave
     
  3. Sloan5556

    Sloan5556

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    Mar 8, 2015
    OK, sure thing. As soon as I get it drawn up I will post it. Thanks.
     
    davenn likes this.
  4. Lenp

    Lenp

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    Sep 8, 2009
    If you are paralleling the led's with a common dropping resistor the voltage drop is too low for them to operate. Led's are current devices . If you need multiple units to light use a separate dropping resistor for each or use several in series with a voltage and dropping resistor to provide enough current. With common led's, if specs are unknown, 20ma is usually a safe current value to use.
     
  5. swagguy8

    swagguy8

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    Dec 10, 2014
    he is right, @Sloan5556
     
  6. Sloan5556

    Sloan5556

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    Mar 8, 2015
    "Led's are current devices."

    That makes sense. I am still trying to grasp all this stuff, like series and parallel and such. I have heard some about voltage changing with more than one LED. I'll have to check into it more. And also more than one resister.
    I took some pics that I want to get posted soon.

    Thanks again.
     
  7. Sloan5556

    Sloan5556

    10
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    Mar 8, 2015
    I am doing an more in depth search into LEDs in parallel and series and I found this page, http://led.linear1.org/led.wiz. I put in 9v, 20mA, 3 (forward volts) with 5 LEDs and it gave me three ways to set it up, I chose the "wiring diagram" view.
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009
  9. Sloan5556

    Sloan5556

    10
    3
    Mar 8, 2015
    Great, thanks. That should keep me busy for a while.
     
  10. Sloan5556

    Sloan5556

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    Mar 8, 2015
    I've learned a bit about series and parallel since the last post. The main thing, don't hook the LEDs in parallel , without a resister for each, which is how I had them and now I have managed to burn the two of them out, oooopsy. But I do have three I soldered together in series a couple of weeks ago with a resister (560 ohms) soldered to the anode of the first one and they're blinking bright and strong (with the 9v wallwart). Oh what fun learning is.
     
    Last edited: Mar 9, 2015
    davenn likes this.
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