Vending Machine

[Altera_Forum]

Hi there.  

I have a school project which consists in a vending machine that has 3 products ( diferent prices) and i can only use 4 type of coins.  My idea is to make a FSM ( where each state equals to the sum of coins that i put in the machine). Am i thinkg right? Can you guys help me?

[Altera_Forum]

This is my code so far: 

(coins : 0.10; 0.20; 0.50 ans 1.00)   library IEEE; use IEEE.STD_LOGIC_1164.all; use IEEE.NUMERIC_STD.all;  entity VendingMachine is   port(sel: in std_logic_vector(1 downto 0);  reset,clk,u,d,c,t: in std_logic;  opn: out std_logic;  total: out std_logic); end VendingMachine;   architecture Behav of VendingMachine is  type estados is(s0, s10,s20,s30,s40,s50,s60,s70,s80,s90,s100,s110,s120,s130,s140,s150,s160,s170,s180,s190,s200,s210,opnd);  signal ps, ns : estados;   begin  sync_proc: process(clk, reset)  begin   if(reset = '1') then   ps <= s0;  elsif(rising_edge(clk)) then   ps <= ns;  end if;  end process;     comb_proc: process(ps,u,d,c,t,ns)  begin   ns <= ps;    case ps is  when s0 => --0.00€  if u = '1' then ns <= s10;  elsif d = '1' then ns <= s20;  elsif c = '1' then ns <= s50;  elsif t = '1' then ns <= s100;  end if;    when s10 =>   if u = '1' then ns <= s20;  elsif d = '1' then ns <= s30;  elsif c = '1' then ns <= s60;  elsif t = '1' then ns <= s110;  end if;      when s20 =>  if u = '1' then ns <= s30;  elsif d = '1' then ns <= s40;  elsif c = '1' then ns <= s70;  elsif t = '1' then ns <= s120;  end if;    when s30 =>  if u = '1' then ns <= s40;  elsif d = '1' then ns <= s50;  elsif c = '1' then ns <= s80;  elsif t = '1' then ns <= s130;  end if;    when s40 =>   if u = '1' then ns <= s50;  elsif d = '1' then ns <= s60;  elsif c = '1' then ns <= s90;  elsif t = '1' then ns <= s140;  end if;    when s50 =>   if u = '1' then ns <= s60;  elsif d = '1' then ns <= s70;  elsif c = '1' then ns <= s100;  elsif t = '1' then ns <= s150;  end if;    when s60 =>  if u = '1' then ns <= s70;  elsif d = '1' then ns <= s80;  elsif c = '1' then ns <= s110;  elsif t = '1' then ns <= s160;  end if;    when s70 =>   if u = '1' then ns <= s80;  elsif d = '1' then ns <= s90;  elsif c = '1' then ns <= s120;  elsif t = '1' then ns <= s170;  end if;    when s80 =>  if u = '1' then ns <= s90;  elsif d = '1' then ns <= s100;  elsif c = '1' then ns <= s130;  elsif t = '1' then ns <= s180;  end if;  if(sel = "01") then   ns <= opnd;   end if;     when s90 =>  if u = '1' then ns <= s100;  elsif d = '1' then ns <= s110;  elsif c = '1' then ns <= s140;  elsif t = '1' then ns <= s190;  end if;  if(sel = "01") then   ns <= opnd;   end if;     when s100 =>   if u = '1' then ns <= s110;  elsif d = '1' then ns <= s120;  elsif c = '1' then ns <= s150;  elsif t = '1' then ns <= s200;  end if;  if( sel = "10") then   ns <= opnd;  elsif(sel = "01") then   ns <= opnd;   end if;    when s110 =>  if u = '1' then ns <= s120;  elsif d = '1' then ns <= s130;  elsif c = '1' then ns <= s160;  elsif t = '1' then ns <= s210;  end if;  if( sel = "10") then   ns <= opnd;  elsif(sel = "01") then   ns <= opnd;   end if;    when s120 =>  if u = '1' then ns <= s130;  elsif d = '1' then ns <= s150;  elsif c = '1' then ns <= s170;    end if;  if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;    when s130 =>   if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;  when s140 =>  if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;     when s150 =>  if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;  when s160 =>  if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;  when s170 =>  if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;  when s180 =>  if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;  when s190 =>  if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;    when s200 =>   if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;    when s210 =>   if(sel = "01") then   ns <= opnd;   elsif( sel = "10") then   ns <= opnd;  elsif(sel <= "11") then   ns <= opnd;  end if;  when opnd =>  opn <= '1';   when others =>  ns <= ps;  end case;  end process;    end Behav;

[Altera_Forum]

Well I haven't checked your code, but your idea is fine.

[Altera_Forum]

It's probably better keep a total, say a 16 bit number of cents. What you have will use up quite a few resources. Fewer resources = cheaper chip. What happens in your design when someone puts $2.25 or $5.00 in the machine? 

 Edit: Fewer resources is relative. Your code as it is now will fit in any modern CPLD. It's better to learn to be frugal with resources at all times. It is always easier to design for fewer resources in the first place than it is to trim down a design that is using too many.

[Altera_Forum]

Similarly to the above remark, seems like wanted to create 1 state for each possible value, which is a real waste if compared to store the sum within 3 unsigned variables, 1 variable per product. In addition, it also would be better you drew a short draft of your design.

[Altera_Forum]

I agree with andre_teprom making a drawing of your design helps in understanding what you are doing. Once you have drawn your state machine you can look at states that are identical and have paths to the same destination under the same conditions. These can be simplified into one state. If you have your drawing, then write the code. It also helps in spotting dead ends or unwanted loops.

[Altera_Forum]

This is a school project, i can't use $5.00 ( five dollars ? we use euros) because we have some restrictions, like, i can only use 4 coins (and i chose 0.10€, 0.20€, 0.50€ and 1.00€) and I can only have 3 products, with random prices, so i thougt that the max price that someone can put in the machine was 2.10€, since the the product with the highest price is 1.20€.

[Altera_Forum]

--- Quote Start ---  It's probably better keep a total, say a 16 bit number of cents. What you have will use up quite a few resources. Fewer resources = cheaper chip. What happens in your design when someone puts $2.25 or $5.00 in the machine?  Edit: Fewer resources is relative. Your code as it is now will fit in any modern CPLD. It's better to learn to be frugal with resources at all times. It is always easier to design for fewer resources in the first place than it is to trim down a design that is using too many.  --- Quote End ---    This is a school project, i can't use $5.00 ( five dollars ? we use euros) because we have some restrictions, like, i can only use 4 coins (and i chose 0.10€, 0.20€, 0.50€ and 1.00€) and I can only have 3 products, with random prices, so i thougt that the max price that someone can put in the machine was 2.10€, since the the product with the highest price is 1.20€.

[Altera_Forum]

--- Quote Start ---  Similarly to the above remark, seems like wanted to create 1 state for each possible value, which is a real waste if compared to store the sum within 3 unsigned variables, 1 variable per product. In addition, it also would be better you drew a short draft of your design.  --- Quote End ---      --- Quote Start ---  I agree with andre_teprom making a drawing of your design helps in understanding what you are doing. Once you have drawn your state machine you can look at states that are identical and have paths to the same destination under the same conditions. These can be simplified into one state. If you have your drawing, then write the code. It also helps in spotting dead ends or unwanted loops.  --- Quote End ---    I thought this was the best way... Can u guys help me using a more efficient way?