this project is a vending machine and the final project of logic circuit.

at first machine resets and starts at choose product state.

when the product signal is changed, it goes to insert coin stateand when the drop_coin signal is changed from 0 to 1, the machine sees the inserted coin and adds the amount of the coin to the user's money.

When the check signal changes from 0 to 1 then the goes to the evaluation state and compares the user money and product price. if the money of the user is greater than the price of the product it subtracts the price from the money of the user so the user can use the money that remains in the next purchase, and the machine goes to deliver state and otherwise goes to error state after seeing the posedge check goes to insert coin state and wait for the user to insert more coin to machine.

in deliver state it turns the motor on until the drop_product signal changes from 1 to 0, and then turns the motor off and goes to choose product state and ready for another operation.

module Vendor(
    input [1:0] product,
    input [1:0] coin,
    input drop_coin,
    input reg check,
    input reg drop_product,
    input clk,
    input reset,
    output reg motor,
    output reg [2:0] LED,
    output reg [8:0] money
);

reg [2:0] state = 3'b000;
reg [1:0] cur_product;
reg [2:0] next_state;
reg [3:0] product_1_num = 7;
reg [3:0] product_2_num = 7;
reg [3:0] product_3_num = 7;
reg [3:0] product_0_num = 7;

1. two bit product: shows the product the user choosed
2. two bit coin: shows the coin the user choosed
3. drop_coin: when coin inserted to the machine it becomes 1 for a short time and then becomes 0
4. check: when the user press check button it becomes 1 for a short time and then becomes 0
5. drop_product:when The product falls out of the machine becomes 1 for a short time and then becomes 0
6. clk
7. reset: when 1 resets the machine to state choose product

1. LED: shows the monitor situation
2. motor: shows the motor situation
3. money: shows the money situation

1. three bit state: shows the current state of the machine
2. two bit current product: shows the current product that the user selected.
3. eigth bit money: shows the amount of coin that the user inserted to the machine
4. three bit next state: shows the next state of the machine should goes to it.
5. four bit product_0_num: shows the number of product zero in the machine.
6. four bit product_1_num: shows the number of product one in the machine.
7. four bit product_2_num: shows the number of product two in the machine.
8. four bit product_3_num: shows the number of product three in the machine.

It used a Behavioral coding style. This code has some always blocks and each of them is sensitive to a different signal and does a certain job. For example:

always @(posedge drop_product) begin
    if (state == 3'b011) begin
        next_state <= 3'b000;
        motor = 0;
        LED = 0;
        case (cur_product)
            0:product_0_num = product_0_num - 1;
            1:product_1_num = product_1_num - 1;
            2:product_2_num = product_2_num - 1;
            3:product_3_num = product_3_num - 1;
        endcase
        cur_product = 0; 
    end
end

in this always block in ts checks if the machine is in the state deliver and drop_product signal changes from 0 to 1 it turns the motor off and the LED to 0 and resets the cur_product and puts next_state to 0 and redused the number of the product that delivered.

or in this part

always @(product) begin
    if (state == 3'b000 &&(((product==0)&&(product_0_num>0))||((product==1)&&(product_1_num>0))||((product==2)&&(product_2_num>0))||((product==3)&&(product_3_num>0)))) begin
        cur_product <= product;
        next_state <= 3'b001;
        LED <= 1;
        motor <= 0;
    end
end

when product signal changes it runs this always, if the machine is in the choose product state machine and machine has enough of this product ,it changes cur_product and next_state so the machine goes to the insert coin state and is ready for inserting coins and LED = 1.

some tests were done on the code you can see all of them in test bench, I explain 4 of them here, the rest of the tests are like these ones just the inputs vary in them. I add some features to the machine and make a new test test 5 to show it.

at first the machine resets. LED = 000

at time t=10 the product signal changes so the next state and after it the state changes to 001, LED = 001

at time t=20 the drop_coin changes to 1 so the machine reads the coin signal and increases the money to 20.

at time t=35 the drop_coin again changes to 1 so the money increases to 40.

at time t=45 the check signal changes to 1 so the machine goes to the evaluate state. Because the money is greater than the product price, the money decreases to 30 and the machine goes to the deliver state, and the motor turns on. LED = 011

at time t=55 the drop_product signal changes to 1 so the motor turns off and the machine goes to the choose products state. LED =000

at time t=115 product signal changes to 11 to the machine goes to the insert coin state.

at time t = 125 the drop_cion signal changes to 1 so the machine reads the coin signal and increases the money to 80(the user has 30 cents from the last payment).

at time t=135 the check signal changes to 1 machine goes to the evaluate state but the user money is less than the price of the product so the machine goes to the error state and LED = 100.

at time t = 155 the check signal changes to 1 machine goes to the insert coin state again and the machine waits for the user to input more coins.

at time t=165 the drop_coin signal changes to 1 the machine reads the coin signal and the money increases to 180. at time t=175 the check changes to 1 but this time user has enough money so the machine goes to the deliver state and the motor turns on.

at time t= 185 the drop_product signal changes to 1 so the machine goes to the choose product state and turns the motor off.

at first the machine resets. LED = 000

at time t=255 product signal changes so the next state and after it the state changes to 001, LED = 001

at time t=265 the coin signal changes but because the drop_coin signal doesn't change to 1, it doesn't increase the coin to the user money.

at time t=285 drop_coin again changes to 1 so the money increases to 100.

at time t=295 check signal changes to 1 so the machine goes to the evaluate state. Because the money is greater than the product price, the money decreases to 50 and the machine goes to the deliver state, and the motor turns on. LED = 011

at time t=305 drop_product signal changes to 1 so the motor turns off and the machine goes to the choose products state. LED =00

at first the machine resets. LED = 000

at time t=375 product signal changes so the next state and after it the state changes to 001, LED = 001

at time t=385 drop_coin again changes to 1 so the money increases to 50.

at time t=400 drop_coin again changes to 1 so the money increases to 100.

at time t=410 check signal changes to 1 so the machine goes to the evaulate state. Because the money is greater than the product price, the money decreases to 0 and the machine goes to the deliver state, and the motor turns on. LED = 011

at time t=420 drop_product signal changes to 1 so the motors turns off and the machine goes to the choose products state. LED =000.

at time t=480 product signal changes to 10 to the machine goes to the insert coin state.

at time t = 490 the drop_cion signal changes to 1 so the machine reads the coin signal and increases the money to 50.

at time t=500 the check signal changes to 1 machine goes to the evaluate state but the user money is less than the price of the product so the machine goes to the error state and LED = 100.

at time t = 520 the check signal changes to 1 machine goes to the insert coin state again and the machine waits for the user to input more coins.

at time t=530 the drop_coin signal changes to 1 the machine reads the coin signal and the money increases to 100.

at time t=540 the check changes to 1 but this time user has enough money so the machine goes to the deliver state and the motor turns on.

at time t= 550 the drop_product signal changes to 1 so the machine goes to the choose product state and turns the motor off.