Simple 3 inputs AND Circuit

Discussion in 'Homework Help' started by MSIE, Aug 18, 2014.

  1. MSIE

    Thread Starter New Member

    Aug 14, 2014
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    [​IMG]

    I assigned the following pin number to all inputs:

    Input A - Pin1
    Input B - Pin2
    Input C - Unsure which pin to use
    Vcc - 14
    Gnd - 7

    Since IC 7408 only accepts two inputs each time. Where do i connect the third input (C)?

    Picture Source: From Doctronics
     
  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Why don't you start by looking for what you actually need ?

    Much easier.

    BTW, are you actually going to use a TTL part? They require too much power. Rather dated. Look for LS or CMOS.
     
  3. MSIE

    Thread Starter New Member

    Aug 14, 2014
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    0
    The picture embedded in my first thread. I'm not looking for performance parts. Just want to learn something out of a basic circuit.

    3 inputs connected in 2 inputs AND gate to generate an output. I'm more concerned on where to connect the third input on the IC itself because i'm a little confused right now :confused:
     
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    OK to the performance.

    Since this is homework, I am not sure if you MUST consider that part.

    The reasonable thing is to use an AND gate with three, four or eight inputs. (Unused ones should go to a logic "high" or "1").

    To show you that more do exist.
     
  5. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Maybe you could use both inputs from gate A, plus one input from gate B (and the unused one, to "1").

    Outputs of gates A & B as inputs of gate C. Resulting output is in the output of gate C.

    Are you suposed to test this in a breadboard?
     
  6. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi msie,
    Consider what the Output state of the 7408 2 inp AND will be IF both inputs are high, logic '1'.
    Then think how you would connect a 2nd 7408 to the 1st 7408 in order to get a 3 input AND logic function.

    Do you follow OK.?
    E
     
  7. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    7408 does not have 3 input AND gates.

    Like others said, you have several choices, you simply need to choose one of them:
    * use different ic, that has 3 input AND gate
    * use multiple 2 input AND gates to produce one 3 input AND gate
    Pick one.
     
  8. tshuck

    Well-Known Member

    Oct 18, 2012
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    Looking at this from a Boolean perspective, remember the Boolean associative and commutative properties?

    The associative property, essentially, says (AB)C = A(BC), where the commutative property says AB = BA.

    So, if you are to implement ABC, you can implement it as A(BC), (AB)C, B(AC), or any combination thereof.

    From another perspective, let Y=AB, or the result of one, two-variable AND operation. Then ABC = YC, another operation.

    Once you understand the implications of what this means, knowing which pins to use will become apparent.
     
  9. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    My bad. I should have left for him to do part of the effort to solve the problem.

    Sorry for actually not helping him.
     
  10. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    It's easy to get carried away. I almost posted the full solution schematic.
     
  11. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Almost only counts in horse shoes and hand grenades.
    ☺7
     
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