Specifications

CONSTRUCTION
RUPANJANA
N
ow-a-days electronic voting ma-
chines 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. (Please note that the design being
presented here is not intended to resemble
that of electronic voting machines used
by the Election Commission. If any re-
semblance is noticed between the two, it
is totally unintended.) Features of the
electronic voting machines include avoid-
ance of invalid votes and reduction of
counting time and the consequent expen-
diture incurred 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 (PPI) 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 74LS373 (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 I. Please note that
during I/O read/write instructions in µP
8085, the 8-bit address used is duplicated
on lower (AD0-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 com-
prises the 8085 microprocessor, memory
(EPROM and RAM), and some function
switches. To get an overview of the vot-
ing machine, we shall start with the ex-
planation of the functional switches.
Start switch (S48). 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 0000H).
Clear switch (S52). This switch is
used for clearing the previous count in
memory. When pressed, the RST 5.5 in-
terrupt starting at location 002CH is ac-
tivated. Here the vector (0100H) pointing
to the sub-routine for clearing the memory
contents is stored.
Display switch (S50). 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 (S51). This switch ac-
tivates RST 6.5 interrupt (location 0034H,
containing the jump address 00B6 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 (S49). 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
number of switches need to be wired. The
remaining keyboard switches can be done
away with. In this 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 this 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
JUNOMON ABRAHAM
ELECTRONIC VOTING MACHINE
PARTS LIST
Semiconductors:
IC1 - 8085A microprocessor
IC2 - 74LS373 octal latch
IC3 - 74LS138 decoder/
demultiplexer
IC4 - 27C32 EEPROM
IC5 - 6116A RAM
IC6 - 82C55 programmable
peripheral interface
IC7 - 74LS47, BCD to 7-segment
decoder/driver
IC8 - 7805, +5V regulator
T1-T4 - BC547 npn transistor
D1, D3 - 1N4001 rectifier diode
D2, D4 - Colour LED
SCR1 - BT169
Resistors (all ¼W, ±5% metal carbon film,
unless stated otherwise)
R1-R3 - 330-ohm
R4-R11 - 3.3-kilo-ohm
R12 - 47-ohm
R13, R22, R23- 2.2-kilo-ohm
R14 - 680-ohm
R15-R21 - 68-ohm
Capacitors:
C1 - 10pF ceramic disc
C2 - 0.1µF ceramic disc
Miscellaneous:
Xtal - 3.58MHz crystal
S53 - On/off switch
S0-S52 - Tactile switch
P21 - Piezo buzzer
DIS1-DIS4 - LT542 common-anode
display
- 4.5V battery
TABLE I
Address Map of Devices Used
Address (Hex) Device
0000-01FF EPROM
8000-80FF RAM
C0 Port A
C1 Port B
of 8255
C2 Port C
C3 Control port
Here we have used ports B and A as output
ports and port C as input port.
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