Drive a Bicolor LED

Discussion in 'The Projects Forum' started by JeromeDarshana, Apr 8, 2012.

  1. JeromeDarshana

    Thread Starter New Member

    Sep 17, 2010
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    I wanna drive a bicolor LED from a one output pin of a micro-controller. Any easy method ?
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Question is how u wanna drive it.

    Bicolor LED's has Common anode & common cathode types.
    What do you have ?
     
  3. JeromeDarshana

    Thread Starter New Member

    Sep 17, 2010
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    I have common cathode type but I wanna method to common cathode too
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    recheck ur post
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    If the µC has the current drive capability (and it probably doesn't) you could use something similar to this approach...


    [​IMG]
    .................................................. .......Figure 3.1

    This from Chapter 4 of my article, LEDs, 555s, Flashers, and Light Chasers.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    Bi-color LEDs have two wires with the LEDs connected with one reversed or have three wires with a common anode or a common cathode.

    A micro-controller has a maximum allowed output current of 15mA which is plenty to light a modern bright LED. But many bi-color LEDs are old and dim.
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    If the processor is a PIC type, the max output (source or sink) is 25mA. At least it is for the 16F690, which I just looked up.

    If the LED is the bipolar type (2 LEDs in parallel, oriented oppositely, with just 2 leads) then you can easily drive them off a single pin if you use a circuit similar to Bill_Marsden's middle diagram, but with lower resistance values, say 100ohm. That gives you the Thevenin equivalent of a connection to half the voltage via half the resistance, and your LED should work on that if the power supply is 5V. But it's inefficient in power use, as the resistors conduct all the time.

    If you have the 3-lead kind of dual LED, I think you're stuck. You need 2 processor pins to drive it.
     
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