International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622

NATIONAL CONFERENCE on Developments, Advances & Trends in Engineering Sciences

(NCDATES- 09th & 10th January 2015)

RESEARCH ARTICLE OPEN ACCESS

Implementation of FPGA Based Smart Vending Machine

B Jyothi 1, I. Sarah 2, A. Srinivas 3
1
CMR College of Engineering & Technology , Assoc. Prof, E.C.E Dept., Hyderabad, India
Email: jyothiboorla404@gmail.com
2
CMR College of Engineering & Technology, Asst. Prof, E.C.E Dept., Narsapur,Medak, India
Email: isarahpaul@gmail.com
3
CMR College of Engineering & Technology, Asst. Prof, E.C.E Dept., Narsapur,Medak, India
Email: asrinivas011@gmail.com

Abstract:
A vending machine is a machine which dispenses items such as snacks, beverages, lottery tickets, consumer
products and even gold and gems to customers automatically, after the customer inserts currency or card into the
machine. Vending machines are very common in the countries like Japan, Germany, and U.S. etc. The
requirements of the vending machines are increasing day by day due to the modern and fast life style. The
FPGA based vending machines are more flexible and faster than the CMOS based machines. The FPGA based
vending machine is also programmable and can be reprogrammed whereas in the Embedded based machines we
have to change the whole architecture of the machine if we want to change or enhance the design of the
machine.
In this paper implemention of vending machine using Finite State Machine (FSM) Model is proposed using
VHDL.FSM modelling is the most important part in developing proposed vending machine model as this
reduces the required hardware. In this project MEALY Machine Model is used to model the process for state i.e.
user selection, waiting for money insertion, product delivery and servicing.
Keywords- FSM, VHDL, Vending Machine, FPGA.

I. INTRODUCTION
Vending Machines are used to dispense various machine can be used at various places like Hotels,
products like Coffee, Snacks, and Cold Drink etc. Restaurants and food streets. This reduces the time
when money is inserted into it. Vending Machines and cost.
have been in existence since 1880s. The first The machines usually work, when
commercial coin operated machine was introduced some money (usually coins or paper money) is put in
in London and England used for selling post cards. a slot. Then a button needs to be pushed, or a lever
The vending machines are more accessible and pulled. If there is enough money in the machine, the
practical than the convention purchasing method. selected item will be dropped to a tray, where it can
Nowadays, these can be found everywhere like at be taken out by the person making the purchase.
railway stations selling train tickets, in schools and Older vending machines were mechanical, but most
offices vending drinks and snacks , in banks as ATM new ones are electronic. Many modern vending
machine and provides even diamonds and platinum machines can accept debit or credit cards in addition
jewelers to customers. Previous CMOS and SED to cash.
based machines are more time consuming than the Some products need to be prepared to become
FPGA based machines. The FPGA based machine is available. For example, tickets are printed or
also more flexible, programmable and can be re- magnetized on the spot, and coffee is freshly
programmed. But in microcontroller based machine, concocted. One of the most common form of
if one wants to enhance the design, he has to change vending machine, the snack machine, often uses a
the whole architecture again but in FPGA user can metal coil which when ordered rotates to release the
easily increase the number of products. product.
In this paper a novel approach is proposed to In the Western world, some vending machines
design a Vending Machine with auto-billing dispense personal products, typically in public toilet
features. The machine also supports a cancel feature facilities. The machines in ladies' restrooms typically
means that the person can withdraw the request and sell pads or tampons. The machines in men's rooms,
the money will be returned back to the user. This when they are present, are most commonly for the
sale of condoms, though in some locations they may
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 International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622
NATIONAL CONFERENCE on Developments, Advances & Trends in Engineering Sciences
(NCDATES- 09th & 10th January 2015)

be found dispensing cologne, medicine, small

candies, or even pornography. These are often found
at toilets used by transient persons in high traffic
locations, such as bus stations, shopping centers,
airports and service stations.
Figure 2: MOORE Machine Model
1.1 Operation of Vending Machine
The paper is organized as: section 2 describes the
I. When the user puts in money, money related work. Section 3 relates the implementation of
counter tells the control unit, the amount Vending Machine and section 4 gives the design
of money inserted in the Vending methodology with description of states. Section 5
Machine. and section 6 shows simulation results and
conclusion respectively.
II. When the user presses the button to
purchase the item that he wants, the II. RELATED WORK
control unit turns on the motor and Various researches have been carried out in
dispenses the product if correct amount is order to design the Vending Machines. A few of
inserted. them are discussed here as: Fauziah Zainuddin [1]
proposes a vending machine for steaming frozen
III. If there is any change, machine will return food using conceptual modelling. In which the
it to the user. process of three main states (user selection state,
freezer state and steaming state) has been modelled
IV. The machine will demand for servicing using process approach, which emphasized on the
when the products are not available inside process flow or control logic to construct the model
for steamed buns vending machine application.
the machine.
Conceptual modelling is described in [6]. In [4] the
1.2 FSM (Finite State Machine) [2] [3] concept of automatic mobile payment is discussed.
This concept is based on the short message payment
In a Finite State Machine the circuit’s output is with the main control module M68HC11 and GPRS
defined in a different set of states i.e. each output is module MC35. Thee various methods of designing
a state. A State Register to hold the state of the VHDL based machines are discussed in [2], [3]
machine and a next state logic to decode the next and [9]. Also in [5] the passenger’s requirements
state. An output register defines the output of the for ticketing system are given. In [7] a coffee
machine. In FSM based machines the hardware gets vending machine is designed using single electron
reduced as in this the whole algorithm can be
encoded logic (SEEL). The designed circuit is
explained in one process.
tested and its power and switching time is
compared with the CMOS technology.
Two types of State machines are:

MEALY Machine: In this machine model, the III. IMPLEMENTATION OF VENDING

output depends on the present state as well as on MACHINE
the input. The MEALY machine model is shown In this paper a state diagram is constructed for
in figure 1. the proposed machine which can vend four
products that is coffee, cold drink, candies and
snacks. Four select (select1, select2, select3,
select4) inputs are taken for selection of products.
Select1 is used for the selection of snacks.
Similarly select2, select3, select4 are used for
coffee, cold drink and candies respectively. Rs_10
Figure 1: MEALY Machine Model and rs_20 inputs represents rupees 10/- and 20/-
notes respectively. A cancel input is also used
MOORE Machine: In Moore machine model when the user wants to withdraw his request and
the output only depends on the present state. also the money will be returned through the return
The MOORE machine model is shown in figure output. Return, product and change are the
2. outputs. Return and change vectors are seven bits

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 International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622
NATIONAL CONFERENCE on Developments, Advances & Trends in Engineering Sciences
(NCDATES- 09th & 10th January 2015)

wide. Money is an in/out signal which can be product to be dispensed. This state can be one of the
updated with the total money of all products select1, select2, select3 and select 4. The machine
delivered at a time. Money signal is seven bits can accept only two types of notes i.e. rupees 10/-
wide. Money_count is an internal signal which and 20/-. Let us suppose that the user selects sel1
can be updated at every transition. This signal is input. The machine will firstly check that whether
also seven bits wide. If the inserted money is the products are available in the machine or not.
more than the total money of products then the After this the control unit will move to the waiting
change will be returned through the change output state, where it will wait for the money to be inserted.
Then if rupees 10/- note is inserted then the machine
signal. The products with their prices are shown
will go to state_1 and wait until the desired money is
by table 1. There are also two input signal clk and
inserted. And if rupees 20/- note is inserted the
reset. The machine will work on the positive edge
machine will move to state_2 and then wait until
of clock and will return to its initial state when 30/- rupees are inserted to the machine. When the
reset button is pressed. The proposed vending desired amount is inserted the machine will go to the
machine is designed using FSM modelling and is snacks state and snacks will be delivered at the
coded in VHDL language. The detail of the entire product output. If products are not available in the
signal with their direction and description is machine then the control unit will demand for
shown in table 2. servicing and after service the machine will get
reset. This methodology is explained using a flow
Table 1: Products with their prices diagram shown in figure 3.

S.No. Products Price

1. Snacks 30/-
2. Coffee 40/-
3. Cold drink 40/-
4. Candies 30/-

Table 2: Inputs/Outputs with Remarks

Name Width Direction Description

clk 1 input Clock
Reset 1 Input Syn reset
Sel1 1 input Snacks
Sel2 1 input Coffee
Sel3 1 input Cold drink
Sel4 1 input Candies
Cancel 1 input Cancel
Money 7 inout Total money
Rs_10 1 input Rupees 10/-
Rs_20 1 input Rupees 20/-
Product 1 output Product out
Change 7 output Extra change
Return 7 output Return money

IV. DESIGN METHODOLOGY

The state diagram mainly consists of four states Figure 3: Flow Chart for Proposed Vending
(User Selection, Waiting for the money insertion, Machine
product deliveryand servicing (when
product_not_available=’1’)). Initially when the reset
There is also an additional feature of withdrawing
button is pressed, the machine will be ready for the
users to select the product. This state is the initial
the request if the user doesn’t want to take the
state of the design. After this the user will select the product. When cancel button is pressed then the

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 International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622
NATIONAL CONFERENCE on Developments, Advances & Trends in Engineering Sciences
(NCDATES- 09th & 10th January 2015)

money inserted will be returned to the user  When state_2=> 

through the return output. A money_count signal 
is used for calculating the total money inserted in Rs_10=0 & rs_20=1; 
the machine. And if the money inserted is more
than the money of the product then the extra Change=0; Product=1;
change will be returned to the user. The total
amount of the product taken at a time is shown by Money_count=money_count+20;
the money signal. Similarly the user can select
and get the other products following the above
procedure.  When snacks=>
Money_count>=30;
Product=1;
Description of states Change=money_count-30;
The selection of products and all the states are Snack_count=snack_count-1;
shown below in figure 4.  When service=>
 When initialize=> snack_count=
money_count=0;
4 product<=0;
Change=0;
next_state<=resett;
Product=0;
 When cancel1=>
 When select1=>
Sel1&!sel2&!sel3&!sel4
cancel=1;
When return<=money_count;
product_available=1=>nx_st1<=w Similarly we can select other products (coffee,
aiting1; Cold drink and candies).
When
product_available=0=>nx_st1<=se V. SIMULATION RESULTS
rvice1; The state diagram shown in figure 4 is
 When waiting1=> simulated using Xilinx ISE Simulator. Simulation
When Waveforms for the selection of four products like
rs_10&!rs_20=>nx_st1<=state_1; snacks is shown in figure 5 and 6 respectively
When ! rs_10& with servicing feature when products are not
rs_20=>nx_st1<=state_2; available in the machine and change return
Change =0; Product=0; features when the money inserted is more than the
When money_count>=30 money of the product.
nx_st1<=snacks; Let us take an example that the user wants to
 When state_1=> take Snacks. When one selects sel1 button, the
Rs_10=1&rs_20=0;
machine will check that whether the products are
Change =0; Product=0;
available or not, if available then it will go to the
money_count=money_count+10;
waiting state and wait for total money insertion. If
rs_10 note is inserted it will go to state_1 and if
rs_20 note is inserted it will so to state_2 and
check whether money_count>=30 or not. If the
money_count >- 30 then machine will go to state
snacks and vend the product.
1. Price of the Product is Rs. 3
Return of Rs. 2 after the Cancel (pu) button is
pressed.

Figure 4: Finite State Machine Diagram of Vending Machine

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 International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622
NATIONAL CONFERENCE on Developments, Advances & Trends in Engineering Sciences
(NCDATES- 09th & 10th January 2015)

RTL Schematic:

Fig 5.1 Return Money

2. Product Delivery and Return of Change after
Rs. 4 insertion.

Fig 5.5 RTL schematic of Vending Machine

Logic utilization Used Available Utilization

Number of Slices 228 3584 6%
Fig 5.2 Product delivery and Return of change Number of Slice flip flops 98 7168 1%
Number of 4 input LUT’s 432 7168 6%
3. Product Delivery after Rs. 3 insertion
Number of bonded IOB’s 31 173 17%
Number of GCLK’s 1 8 12%
Table 3: Device Utilization Summary

The comparison of VHDL based machine with

the CMOS technology based machine on the
basis of switching speed is shown in table 4.

Table 4: Comparison of Switching Speed

Fig 5.3 Product deliver Using

Parameter using FPGA Single Electron CMOS
Device (SED) technology

Switching Speed 9.3 ns 12.53 ns 300ns

VI. CONCLUSION
When we realized that we have at last made a
code that could actually work as a user friendly
vending machine. This code can actually provide a
variety of options to the user and also return him/her
Fig 5.4 Product delivery
the balance money. This verilog code has been
successfully verified using the Xilinx ISE 9.2i tool

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 International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622
NATIONAL CONFERENCE on Developments, Advances & Trends in Engineering Sciences
(NCDATES- 09th & 10th January 2015)

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