DC Voltage indicator using dual/triple colour LED

Discussion in 'General Electronics Chat' started by lisahxw, Feb 23, 2009.

  1. lisahxw

    Thread Starter New Member

    Feb 23, 2009
    2
    0
    Hi everyone, I am new here. Just wonder if anyone know how to design a DC voltage indicator using dual colour or ideally even triple colour LED, so it is function as follow:

    Vout<11V red
    {11V<Vout<12.5V orange}
    Vout>12.5V Green

    And anyway to make the reference adjustable.

    Thanks.:)
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    You will need two comparators.
    One that switches the red off above 12.5 Volts and
    one that switches the green off below 11 Volts.

    Greetings,
    Bertus
     
  3. lisahxw

    Thread Starter New Member

    Feb 23, 2009
    2
    0
    Erm............ I thought using comparators need a reference voltage. But in this case, it is to indicate the battery voltage level and there won't be an other power supply. How could the circuit designed to "know" the reference voltage?
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    A comparator needs a reference.
    This can be a zenerdiode for instance.
    The other input will be the measure input.
    Depending on the inputs the comparator will switch on or off.

    Take a look at this page of the AAC eBook.
    http://www.allaboutcircuits.com/vol_3/chpt_8/3.html

    Greetings,
    Bertus
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Use an LM3914 bar-graph LED driver IC. It has 10 comparators (use only 3 if you want) and an adjustable regulated reference voltage.
     
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