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Discussion in 'Beginner Electronics' started by rda, Jan 29, 2004.

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  1. rda

    rda Guest

    Hi there, excuse my ignorance, but I cannot for the life of me remember the
    polarity of LED's. Is it the long or shorter of the legs that is the +ve.

  2. UncleWobbly

    UncleWobbly Guest

    I never could remember this... has the body got a flat on the lower edge?
    this is the cathode (-)
    having just quickly grabbed one and checked, the short leg is next to the
    flat so the short leg is -ve
  3. Activeviii

    Activeviii Guest

    if you go to the maplins web site and look at the leds in there you will see
    all the diagrams you need
    hope this helps.

  4. Thrashbarg

    Thrashbarg Guest

    Another method is to hold the LED up to the light and look at the terminals
    within the LED. The bigger piece is the cathode, the smaller is the anode.I
    use this when the legs have been cut.
  5. Look through the LED. The big bit is a cup, with the active bit in the
    bottom of it.

    The Kup is the Kathode... :)
  6. nemo

    nemo Guest

    A good Mnemo-nic way of remembering it! :eek:)

    BTW - providing you've got a ballast resistor in series, you can find the
    correct polarity by trial and error without damaging the LED. I keep a PP3
    9V battery with a 560Ohm resistor soldered to it on my bench for precisely
    this purpose. Being a skinflint, I often use recycled LEDs stripped from off
    of PCBs with both leads the same length.

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