3 Switch LOGIC Circuit

Discussion in 'Homework Help' started by johncena, Aug 29, 2010.

  1. johncena

    Thread Starter Member

    Aug 15, 2010
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    0
    We need to setup a 3 switch wherein if more than 2 switch are open, the LED will light. Materials should only be 2 transistor NPN and 2 PNP transistors, LED , resistors and wires. If switch is off it will generate negative volt, else, it will give +5 volts ( There is also a separate - and +5 volts source aside from the switches) (Switches are from the Digital trainer). It doesn't matter where LED will glow very bright, as long as there is a light on led, it counts as on.

    Is it possible to make a circuits with only 2 NPN and 2 PNP transistors?
     
    Last edited: Aug 29, 2010
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    What have you been able to come up with on your own so far?

    hgmjr
     
  3. johncena

    Thread Starter Member

    Aug 15, 2010
    32
    0
    still unsuccessful. I made 3 AND gates and 1 OR gate (without doing the required limited transistors). But the output is wrong
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Have you drawn up a truth table? It is then possible to make a network to match.

    Can you use diodes, or are transistors it?
     
  5. johncena

    Thread Starter Member

    Aug 15, 2010
    32
    0
    Here:

    0 0 0 = 0
    1 0 0 = 0
    0 1 0 = 0
    0 0 1 = 0
    1 1 0 = 1
    1 0 1 = 1
    0 1 1 = 1
    1 1 1 = 1

    No diodes, just Transistors as a Basic ON and OFF switch (General Purpose Transistors)
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Just a suggestion, whenever you make a logic diagram use a sequential count. Patterns show up better too.

    0 0 0. 0
    0 0 1. 0
    0 1 0. 0
    0 1 1. 1
    1 0 0. 0
    1 0 1. 1
    1 1 0. 1
    1 1 1. 1

    Ever study how to build a Schmitt trigger using transistors? You may be able to set up a voltage comparator threshold using resistors and transistors.
     
  7. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    I really can't see how this can be materialized. Give me 6 npn's and 4 pnp's and sure, I 'll do it, but with such a tight budget I'm at a loss.
     
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