LED cathodes circuits doesn't work

Discussion in 'General Electronics Chat' started by PSnetwork, Apr 1, 2013.

  1. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    0
    i have got today my RGB LEDS cathodes
    so i took 4 cathodes, than wired them together, + - + -
    than cut off a molex head took the red cable (+12v) and wired him to -
    and the black cable (-) to the last + cathode. after all this i used soldering iron.
    than i turned on my pc and nothing, no circuit working. what i did wrong ?

    these the cathodes here
    and how they work

    sorry for my english :/
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    I am not sure how you connected them, but be glad they didn't light. If you didn't use current limiting resistors, they would have burned out.

    Post a diagram of how you connected them. It doesn't have to be pretty.
     
  3. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    You need 510 Ohm resistors as well.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    You need to wire the cathode to -ve , and the anodes to +ve, use a 470 ohm resistor in series on each anode and then connect it to the power supply and then they will work.
     
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  5. MrChips

    Moderator

    Oct 2, 2009
    12,447
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    If you didn't use current limiting resistors, say bye-bye to your LEDs.

    Luckily, you wired the power to the LEDs backwards so nothing happened.
     
  6. PSnetwork

    Thread Starter Member

    Apr 1, 2013
    30
    0
    guys. i dont have resistors, and i dont know whats that. look i am really amateur in electronics .

    here's the diagram
    [​IMG]

    so whats the problem?
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,447
    3,363
    Amazing that you learned about LEDs before resistors!:eek:

    It's time for you to click on the first tab at the top of this page!
     
  8. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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  9. Tealc

    Member

    Jun 30, 2011
    140
    10
    That YouTube video gives bad advice and the guy doing it clearly knew nothing about LEDs or electronics.

    The item he copied probably had a resistor under the heatshrink.

    Anyway you still wired them backwards and to the wrong voltage wires. The yellow is your +12v and the black your 0v. You'll need a resistor for each colour of led.

    If you do not use a resistor in a led circuit one of the devices will hog all the current and eventually fail. It might only take seconds, or could be hours but one will blow.

    There are led resistor calculators on the Internet that will give you the correct values to get, based on the configuration you want.

    I might go something like
    +12v ----->|----->|----->|----330ohm-----0v for red led
    +12v------>|----->|----->|----220ohm-----0v for green led
    +12v------>|----->|----->|----150ohm-----0v for blue LEDs

    Or resistor values close/slightly higher.
     
    Last edited: Apr 1, 2013
  10. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    0
    between every 2 cathodes should be 1 resistor ? so how many resistors should be in 4 LEDS circuit ?
     
  11. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    No you only need one in such a case.

    Why do you want to wire them in series?

    The single colors as such share a cathode.
    You need one resistor for each color.

    If you wire more LEDs in series, normally you need only one resistor.
     
  12. Tealc

    Member

    Jun 30, 2011
    140
    10
    Ah yes if they are common cathode then the resistor needs to be on the anode side.

    First work out how you want them wired. Having a few LEDs in series can reduce the amount of power used by your circuit and also the amount of energy wasted as heat.

    And in my ASCII circuit there were 3 LEDs in series, not two.
     
  13. PSnetwork

    Thread Starter Member

    Apr 1, 2013
    30
    0
    can you show me a diagram how should be the circuit with the resistor and the 4 common cathodes? it will help
     
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