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Possible to use LM3914 with bicolor LED?

Discussion in 'Electronic Basics' started by Impmon, Nov 30, 2003.

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  1. Impmon

    Impmon Guest

    I'm doing a serious cosmetic tweak on the front of my PC and I wanted a
    visual display of sound output. (It'll be on the 5.25" faceplate with
    temp sensor and fan RPM)

    I wanted to use a bicolor LED and hook it to an LM3914 dot/bar display
    driver (in bar mode). Since there are only 2 leads per bicolor LED, no
    common anode or cathode so I'm going to use a hex inverter like 7404 or
    4049 so it'd always be red or green. (see for example) The
    question is can the LM3914 drive an inverter?

    My plan was to hook the display driver to the sound output (one for each
    left and right audio) and have the display indicate 0v to 1v (all green
    on 0v, 1 red bar on bottom & rest on green on 0.1v, 2 red bars on bottom
    and rest green on 0.2v, all red on 1v, etc.) I'm assuming the line out
    is 1v max (not speaker out, unamplified line out for powered speaker or

    If LM3914 can't drive that, then what can? I could try building one
    using individual op amps and/or resistor network but I don't want big
    circuit, just something small and simple.

    I have tried googling for sound display but all I found were single
    color only.
  2. Rich Grise

    Rich Grise Guest

    Yes, an LM3914 can drive inverters, if you put a pullup on each of
    its outputs. Then, you'd go to kind of a bridge arrangement -
    each output goes to the inputs of two inverters. Use HCMOS inverters,
    like 74HC04 - they can source current for the "other" LEDs.
    Then the output of one inverter goes to one end of one of the
    led/resistor sets, the output of the second inverter goes to
    the input of a third inverter, whose output goes to the other
    end of the led/resistor set. You can do 2 LED's worth with one
    hex inverter.

    Have Fun!
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