1. CURCUIT DIAGRAM

 2. PCB LAYOUTS

3. COMPONENT LAYOUTS

4. THEORY

Now a days EVM are being used effectively. The confidence of the voter in its flawless working is gradually building up and these machines are thus becom ing quite popular throughout the coun try. Features of the elec tronic voting machines include avoidance of invalid votes and reduction of counting time and the consequent expenditure in curred on manpower deployment.

Hardware description

The voting machine circuit being described here is designed around Intel's basic 8085 microprocessor.

 It has two main units:

(i) control and processing unit, and

(ii) keyboard and display unit.

Keyboard and display are interfaced through a general-purpose programmable peripheral interface (PPD IC 8255. The system monitor programs are stored in 2732 EPROM. RAM 6116 is used for stor ing counts and a portion of it is also used as stack. IC 74L8373 (octal D-type latch) is used for segregating the lower order address bits from multiplexed address data bus of 8085. Two of the higher order bits are decoded by 74LS138 to generate chip select signals for IC4 through IC6. The address/address range for each de vice is shown in Table 1.

During I/O read/write instructions in Microprocessor 8085, the 8-bit address used is duplicated on lower (ADO-AD7) as well as higher (A8 A15) address bus.

The system runs with a clock fre quency of 1.79 MHz (i.e. half the crystal oscillator frequency of 3.58 MHz). Auto reset facility is incorporated in this sys tem for avoiding corruption of count dur ing interruption in power supply. This is achieved by using the latching property of SCR. A battery backup (3x1.5V UM3 type) is provided for RAM chip to retain the latest counts.

The Control and processing Unit comprises the 8085 microprocessor, memory (EPROM and RAM), and some function switches. To get an overview of the voting machine, we shall start with the explana tion of the functional switches.        

Start switch (848). When the circuit is initially powered on, it is in reset state due to the auto reset facility. If you want to activate the system, press the 'start' but ton. This causes the SCR to conduct and take RS pin 36 of 8085 to logic 'high'. As a result 8085 microprocessor becomes ac tive. In this state, the microprocessor will execute the booting program (starting at location/address OOOOH).

Clear switch (852). This switch is used for clearing the previous count in memory. When pressed, the RST 5.5 in terrupt starting at location 002CH is invoked. Here the vector (0100H) pointing to the sub-routine for clearing the memory contents is stored.

Display switch (850). This switch activates RST 7.5 interrupt (location 003CH) containing vector for executing 'display routine' used for displaying the count of the votes polled by any candi date. If one wants to see the count of a specific candidate, 'display' switch is pressed first, followed by the depression of the switch on the keyboard allocated to the specific candidate.

Count switch (851). This switch ac tivates RST 6.5 interrupt (location 0O34H, containing the jump address OOB6 for count subroutine) for activating the mi croprocessor to accept only one vote for a candidate, by depressing the keyboard switch allocated to that candidate.

Reset switch (849). If any malfunc tioning is observed during the operation of the voting machine, the RESET switch can be used to shut down the system.

This voting machine has the capabil ity to handle up to 48 candidates. Each switch on the keyboard represents one specific candidate. If one does not need all the 48 switches, only the required num ber of switches need to be wired. The re maining keyboard switches can be done away with. In tills unit, LED D4 is used to indicate that the system is ready for accepting the next (one) vote.

Operating Procedure

1. Switch 'on' the power, using switch S53.

2. Press 'start' button.

3. A software-based security feature has been added in tills system which re quires one to enter the password digits via the keyboard for getting access to the machine for its operation. (The maximum length of password is seven digits, but it can be changed by adjusting some values in the system software.) At present, only three-digit password is used. If the password digits entered via keyboard equal the pass word stored in the EPROM, LED D2 glows to give ac cess for operation of the ma chine.

4. If the entered password is incorrect, press RESET button (849) and proceed again from the first step.

5. Clear the previous content of count memory by pressing 'clear' button (852). Clearance of memory is indicated by symbol 'u' in the display.

6. Now press 'count' switch 851. The display of symbol' C' and the glowing of LED D4 would mean that the system is ready for ac cepting one vote. (Please note that the 'count' switch is placed under the control of electoral staff so that it is satisfied with the identity of the voter before allowing him/her to cast his/her vote.)

7. Now, the voter can cast his/her vote by press ing the appropriate key board switch allocated to the candidate of his/her choice. The acceptance of the vote by the system is acknowledged by a beep sound as well as the dis play of the symbol in the display and 'off' condi tion of LED D4.

8. Steps 6 and 7 have to be repeated for casting a fresh vote.

9. If the count of any particular candidate's votes (count) is needed to be displayed, press 'display' switch and then the switch corresponding to the specific         candidate on the keyboard.

10. Reset the system.

11. Switch 'off the system.

6. Software description

The system programs are stored in the EPROM. The entire software VOTE.LST is divided into five modules, namely, booting, display, clearing memory, counting and keyboard. The operation of each module can easily understood with reference of flowchart.

Booting:-  This module initializes the stack pointer, 8255- PPI, verifies the password entered via the keyboard, and initializes the interrupts.

Display:- This module uses the interrupt service subroutine at RST 7.5. This is used for displaying the count (votes) of the candidates.

Clearing Memory:- This module is invoked via interrupt service subroutine RST 5.5. It is used to clear the count memory.

Counting:- This module uses the in terrupt subroutine RST 6.5. It ac tivates the microprocessor to accept only one vote. If the count of any candidate exceeds ‘9999’, it will produce a continuous beep sound and display the symbol, and then onwards the system will not be ready for accepting any further vote. Thus, the maximum number of votes that can be registered against any one candidate should not exceed 9999. This is the limitation in the present design.

Keyboard:- This module is used for further checking key closure and generating the binary value corresponding to the closed switch.

Password security

This voting machine has a password op tion. The length of the password is limited to a maximum of seven digits. The password should be decided before burning the program in EPROM. Password checking is performed during execution of booting program. For, enter ing the password, the same keyboard switches are used that otherwise represent specific candidates.

For the setting of password (PW), the length of password is chosen first and then it is loaded into register C using instruc tion ‘MVI A, length’ in the booting pro gram. The digits of the password are stored in memory locations 00F9H to 00FFH. Each of the PW digits chosen is multiplied by 4 and converted into hex format, and then stored in consecutive memory locations starting from 00F9H. For example, in the present listing the PW is 1, 4, 8; the length is loaded as 03 in register C and the hex data loaded at  specified locations is as follows:

EPROM                Hex                Conversion                PW

Location                 data                                                digit

        00F9                 04                04H        04         4x1                1

        00FA                 10                10H         16          4x4                4

        00FB                 20                20H         32         4x8                8

SOURCE

7. COMPONENT LIST

8. FABRICATION OF PCB

The term PCB stands for Printed Circuit Board (PCB) which is used for drawing the circuit so that component mounting is made.

After the circuit diagram of the project was made then we were made to draw the circuit diagram on the PCB for this purpose we used a copper clad laminate and then we did the following processes:-

1. Preprocessing

2. Photolithography

3. Etching

4. Drilling

5. Board testing

6. Board finishing

Before starting the above process following considerations were taken in the account:-

  1. Diameter of pin hole should be equal to 0.8 mm.
  2. The path around the pin hole should be circular and should be of 3mm in diameter.
  3. Minimum distance between any two mounted components should be about 5mm.
  4. Distance between two pins of the resistance is decided according to the power of the Resistance:-

  1. For 14 watt resistance: distance between its pin should lie    between 12mm to 15mm.
  2. For 42 watt resistance: distance between its pin should lie between 15mm to 20mm.
  3. For 1 watt resistance: distance between its pin should lie between 20mm to 25mm.
  4. For variable resistor: distance between its pin should be 20mm and the diameter of the path around the pin hole should be 5mm.

  1. For an IC the, width in most cases should be 7.5mm but for   some ICs the width varies according to the width of the ICs. The centre to centre distance between any two adjacent pins of the IC should be 2.5mm (in most of the cases).

  1. For the capacitors the distance between the legs depends on the type of the capacitor:-

  1. For ceramic capacitor: distance between the legs should be 5mm to 10mm for voltage less than 250V and for more than 250V the diameter should be 10nlln to 15mm.
  2. For electrolytic capacitors: distance between the legs depend on the value of the capacitor:-
  1. For the value less than 10uF the distance should be 5mm.
  2. For the value more than 10uF and less than 100uF the distance should be minimum of 8mm.

  1. For diodes the distance between the legs should be of l5mm to 20mm and the distance between the legs of two adjacent diodes should be 7mm.

  1. For the transistor we have the legs in triangular form and the distance between the collector and emitter should be 6mm while the distance between the base and collector or base and emitter should be 3mm (1/2 of the distance between collector and emitter).

  1. Design of the circuit is such that it occupies minimum possible space.

10. Proper care is taken so that there is no short circuit between the components.

Now taking in the account above consideration we start the process of fabrication of PCB which consists of the following steps:-

  1. Drawing of the circuit on PCB:-.

  1. Firstly the circuit is drawn on a graph paper taking in account of all the considerations.

  1. Then the imprint of this graph paper is taken onto the PCB with the help of a carbon paper or a butter paper.

  1. Then the copper clad laminate is cut up into the required size of the circuit of the project.

  1. Then the circuit lines are darken with the help of paint or a marker. This is done to ensure that the, path docs not get removed during the etching process.

2. Etching process:-

            Etching process is the process to remove the unwanted. Copper from the copper clad laminate. This is done with the help of etching solution (mostly we use Ferric Chloride) Etching solution is a non organic compound used for chipping away the copper from the area of copper clad laminate other then the tracks or painted paths.

This etching solution is kept in a container large enough to enclose the PCB. The PCB is then drowned in the etching solution and is kept for 30-45 minutes. Gradually the unwanted copper gets removed from the PCB and we obtain only the painted tracks on the PCB.

These tracks are then cleaned with the help of spirit solution so that we get copper tracks.

3. Drilling:-

After the etching process, PCB is taken for drilling the holes on PCB. Needle used in the drilling machine should be of appropriate diameter. Before the drilling points should be

Marked where the holes would be drilled, this is done with the help of a nail and a light hammer. After this the holes are made in the PCB with the help of drilling machine at the already marked places.

4. Testing of board:-

After the drilling is made the board made is tested that the copper tracks we have made are working properly or not and the drilled holes are properly placed or not. The testing usually consists of visual inspection and continuity testing.

Visual testing is carried out to ensure proper track width and proper conductor pattern.

Continuity testing will ensure proper connections between different points.

                                           

                 

                         

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