Voltage comparator circuit

Discussion in 'The Projects Forum' started by javajoe, Mar 29, 2011.

  1. javajoe

    Thread Starter New Member

    Mar 29, 2011
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    I have a project that involves using a simple DC circuit that will test for three voltage ranges and turn on three different LED's within each range. For example: Red LED would turn on when Vin drops below 5Vdc, Green LED would turn on with Vin in the range 5Vdc to 6.9Vdc, and Amber LED would turn on with Vin at or above 7.0 Vdc. I have 12 Vdc also coming in that could be used as a reference voltage which can be divided to give 3 ref. voltages. I also have an OP amp(339) to use as the comparator. It would be nice if each LED would lite up independently when in each range. So I'm looking for the green LED to lite up at that 5 to 6.9 Vdc range and turn off if the other voltages are encountered either High or Low. A circuit diagram would be helpful for me to get my brain around this problem.
    Thanks :confused:
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
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    You won't be able to fulfill your requirements with one OpAmp or Comparator. Here's the easy way using a uC.
     
  3. javajoe

    Thread Starter New Member

    Mar 29, 2011
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    Won't this circuit work? :(
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    A quad comparitor should be able to do it I would think. Basically one for low, one for high, and a diode OR gate for when both outputs are low. 3 comparitors,several diodes and resistors.
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    You were one click away :) On the PDF you posted near the bottom it says "related circuits" one of them takes you to this; http://www.aldinc.com/pdf/cd_23001.0.pdf

    Now, its for a four way comparator circuit, but if you just eliminate one of them you will have your three way comparator :)
     
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  6. javajoe

    Thread Starter New Member

    Mar 29, 2011
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    Thanks for that info I'll try this and let you know of the results.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    If you use that circuit for only three of the four comparators you should ground the unused input pins, the unused out put can/should be left floating.
     
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