Project help

Discussion in 'General Electronics Chat' started by shortbus, Apr 16, 2010.

  1. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
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    I am working on a on going project and need to know if this will work as I intend it to. It's based loosely on a Bill Marsden circuit, just changed to suit my project.

    The A and B are from the rest of the circuit. I want the led to light when either of the voltages feeding the LM339 go below a set point. What I don't know is can two circuit branches control one led?

    As always any help is appreciated, thank you, cary
     
  2. Bychon

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    Mar 12, 2010
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    Yep that'll work.
     
  3. Wendy

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    Mar 24, 2008
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    Open collector is a common way to create a gate. In this case it is a type of NAND, since both outputs have to be high to turn off the LED. It is used a lot by TTL.

    I agree, looks good.
     
  4. Audioguru

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    Dec 20, 2007
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    The circuit will work backwards to what you want.
    The LED lights when an input goes above the reference voltage, not below.
     
  5. Wendy

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    [​IMG]

    If the input (which is negative) goes above the positive input then the output of the comparitor goes low. A low on the base of the transistor will turn on the LED.

    AG is right. Just reverse the inputs, easy fix.
     
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  6. shortbus

    Thread Starter AAC Fanatic!

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    Thanks Everybody!!

    Yeah after I posted I saw my 339 inputs were back wards. Not thinking when I drew schematic.

    I want to thank you all on this forum for all the help and sharing of knowledge that you do!
     
  7. Wendy

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    Nice schematic. :)
     
  8. retched

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    Dec 5, 2009
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