Homework X, a Vending Machine

Objectives

1. Develop a circuit that can serve as the basis for a vending machine.

Discussion

You are living an Danland, where there are four coins
• The 1 Danari coin
• The 5 Danari coin
• The 10 Danari coin
• The 25 Danari coin
You are to develop a simple circuit for a vending machine. You should assume the following:
• You have a device that will detect coins as they are deposited, it will provide the following input:
  • cv, a two bit line containing the coin last deposited

  • CV	Coin Value
    00	1
    01	5
    10	10
    11	25

  • cd, a one bit line indicating that a coin has been deposited.
  • You can assume that when cd raises from 0 to 1, the data on cv indicates the coin value.
  • If you are interested, this video shows someone making a device that could do this.
• A button selector
  • With a choice of 7 buttons (labeled 0 - 7)
  • And a button labeled vend.
  • This produces two inputs to your circuit
    • vs a 3 bit line that indicates the user's choice 0-7
    • v a 1 bit line that goes from low to high when the user wishes to make a purchase.
  • You may assume that when the v line rises from low to high, the vs lines contain a valid value representing the user's selection.
• You should support an additional reset line, that resets your circuit.
• Your circuit should contain a memory that contains product descriptions. For each of the 8 products, this should include
  • A three letter description
  • An 8 bit price, nothing can cost more than 255 Danari (The plural of Danari is Danari), however for simplicity do not make any item cost more than 127D
  • In my test machine, I supported the following products

    Code	Description
    0x43414e64	100D CAN
    0x4341527D	125D CAR
    0x43415401	1D CAT
    0x444f477f	127D DOG

  • 
• Your circuit should only work up until an item has sufficient coins deposited to purchase the item, you do not need to make change.
• Your circuit should support the following input buttons
  • 
  • Item Selection simulates vs above
  • Vend simulates v above
  • Coin Value simulates cv above
  • Coin Deposited simulates cd above
  • Reset is the 1 bit reset line, and resets the entire machine on 1.
  • In this case, the customer has selected item 0, and has deposited one coin of type 2 (10D coin)
• You circuit should display
  • The current item selected (as pictured above, bot text and price)
  • The State of the machine
  • 
  • Selected Cost: the cost of the item currently selected, set only after Item Select has been pressed.
  • Amount Deposited: the amount the customer has placed in the machine
  • Deposit More Coins: red when the customer has placed insufficient funds to make the current purchase.
  • Deliver Goods: red when the customer has placed exactly the correct value of coins or more for the current purchase.
  • Change Due: red when the customer has placed a larger value of coins than the value of the current purchase.
  • In this case, the customer is purchasing a 100D item, has deposited 65D value of coins.

Notes

• Use only circuits/components we have discussed except
  • You may use the comparator (under Arithmetic)
  • You may use the constant value (under wires)
  • You may use an adder and/or a subtractor
• Item price changes as the customer scrolls through the items.
• Selected cost changes only when the customer selects vend.
• You should have 8 items in your inventory, the first four should match mine.
• I only used three or gates, everything else was accomplished with components.
• Don't make any price higher than 127D
• Don't worry about overflow.

Submission