Basic vending machine logic circuit, with visual

[jmckennon]

1. Homework Statement
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. Homework Equations



3. The Attempt at a Solution

I'm just beginning in digital logic so i don't 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

 

[mmwave]

.

Thank you for your post. I understand the importance of designing a functional and efficient circuit. Based on the information provided, here is a possible solution for the vending machine logic circuit:

1. Inputs: The three logic switches (nickels, dimes, and quarters) will serve as inputs to the circuit.

2. Coin Detection: Each switch will be connected to its own AND gate. The output of each AND gate will go to a common OR gate. This way, when any of the switches is turned on, the OR gate will receive an input and trigger the next step.

3. Water Dispensing: The output of the OR gate will go to an AND gate, along with the input from the nickel switch. This AND gate will also receive an input from a NOT gate connected to the dime switch. This means that when the nickel switch is on and the dime switch is off, the AND gate will produce an output, triggering the water dispenser.

4. Beer Dispensing: The output of the OR gate will also go to another AND gate, along with the input from the quarter switch. This AND gate will also receive an input from a NOT gate connected to the nickel switch. This means that when the quarter switch is on and the nickel switch is off, the AND gate will produce an output, triggering the beer dispenser.

5. Indicator Lights: The output of the AND gates for water and beer dispensing will go to two separate indicator lights, which will light up when the corresponding drink is dispensed.

6. Amount Calculation: To ensure that the correct drink is dispensed based on the amount of coins inserted, we can add an extra AND gate to the circuit. This AND gate will receive inputs from all three switches and produce an output only when the total amount inserted is between 15 and 30 cents. This output will go to the water dispenser AND gate, ensuring that only water is dispensed for this range of coins.

I hope this helps in understanding the circuit design. It is always helpful to start with a truth table and then work on building the circuit step by step. Good luck on your exam!