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Basic vending machine logic circuit, need help with visual

  1. Sep 15, 2008 #1
    1. The problem statement, all variables and given/known data
    Design a logic circuit to simulate the circuitry that might exist in a vending machine. the vending machine accepts inputs of nickels, dimes, and quarters but only one of each. It dispenses water and beer. Use three logic switches to simulate the coin detectors one each for nickels dimes and quarters. and two indicator lights for water and beer. for amounts less than 15 cents, no output is given. for amounts of 15-30 cents, water is dispensed. for amounts over 30 cents, beer is dispensed.

    This problem was assigned in my 3 hour lab period today, and none of the groups were able to draw out a sketch of the possible AND, OR, and NAND combinations that could make this circuit work.

    2. Relevant equations

    3. The attempt at a solution

    I'm just beginning in digital logic so i dont have much logical background. I started off by making a truth table

    N D Q W B
    0 0 0 0 0
    0 0 1 1 0
    0 1 0 0 0
    0 1 1 0 1
    1 0 0 0 0
    1 0 1 1 0
    1 1 0 1 0
    1 1 1 0 1

    we used 1 7408 series AND gate chip, but I don't really know how to draw out the circuit. It's worth a hefty amount of points on my exam wednesday morning so any help would be appreciated in drawing how this circuit would work
  2. jcsd
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