led issue

Discussion in 'The Projects Forum' started by servo, Mar 12, 2012.

  1. servo

    Thread Starter Member

    Aug 11, 2011
    31
    0
    Hi, everyone.
    I have a backlit panel meter that should glow a pleasant green. However, when I hook it up, it glows a kind of orange and slowly starts fading to red while dimming. What would make an led do that?
     
  2. tw34kd

    New Member

    Jul 17, 2010
    8
    0
    How are you hooking it up? Sounds like you omitted using a resistor.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,129
    3,050
    I don't know of any practical way to shift the color of an LED, only its brightness. Curious to see how this turns out. Are you SURE the lighting is an LED? Maybe there's a plastic filter on the light, and that piece of plastic has changed color with age?
     
  4. servo

    Thread Starter Member

    Aug 11, 2011
    31
    0
    It's one of these.

    http://www.murata-ps.com/data/meters/30lcd.pdf

    It's right out of the box and after checking around there may be too much current being pulled through it, though I can't find enough to be sure. Yahoo Answers isn't the most reliable source. I don't know why, but something must be up with the LED because the rest of the meter works just fine. It's also got a converter board on it so it's being run off of 5VDC.
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    If the supply is +5V then grounding pin 2 lights up the backlighting LEDs. If the supply is +9V then the LEDs will be close to their maximum allowed current.

    The voltage converter converts the positive 5V supply to a negative 5V supply for the opamp in the circuit.
     
  6. servo

    Thread Starter Member

    Aug 11, 2011
    31
    0
    Through the circuit I have 24V stepped down to 5V going into the converter. I jump pin 2 to pin 3 which illuminates the backlight, but it's orange and the meter starts acting funky. The orange light starts to fade to red before going out completely and once it does, the meter functions as it should. It's strange. If I leave the jumper off, the meter functions as it should.
     
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