Voting machine with PC using the Hyper Terminal communication system

Here is a prototype of voting machine. Micro controller AT89C51 is used for controlling the voting operation. It has a Monitor display for showing the status of voting by interfacing the voting machine with the PC. Every operation on the voting machine is defined and displayed on the Computer Monitor. For connecting the Voting machine with PC Hyper Terminal communication system can be used.

Construction and working of Circuit:

The figure above shows the basic circuit diagram of the electronic voting machine system using microcontroller AT89C51. The power supply for the circuit is regulated by the IC7805 and supplied to different parts of the unit. 24C02 is the memory storage IC. The microcontroller unit (MCU) reads the data from the IC 24C02 Via MAX-232 IC the serial communication IC. The MAX -232 IC transfers the data stored in the 24C02 to the secondary memory of the computer via RS 232 cable which is used to setup a communication medium between the computer and the voting machine. The HyperTerminal is the software which is used to view the votes of the user on the computer. The communication between the voting machine and the computer is established with the help of this software. The functions of each section of the circuit are explained in the following sections.

Power Supply:

The power supply unit consists of a step-down transformer (230V AC primary to 0-9V, 250mA secondary), bridge rectifier and voltage regulator. The output of the transformer is fed to bridge rectifier diodes D1 through D4 (each IN4007). The ripple from the output bridge rectifier is filtered by capacitor C1 and fed to regulator IC7805. The regulated output is given to the memory unit, microcontroller unit and data transfer unit, respectively.
When the switch S1 is closed, LED1 glows to indicate the presence of power in the system.

Data Storage:

While the power is put on and as the Vcc arrives the microcontroller unit and the current is provided to the memory IC the program starts to run after resetting the circuit. The user votes to the particular nominee whichever it likes to and then the data provided by the user is stored in the memory IC 24C02. The data stored in the memory IC is then accessed afterwards with the help of the serial communication IC MAX-232 and can be viewed on the computer via a HYPERLINK communication software.
To prevent data corruption and inadvertent write operations during power up, a Power On Reset (POR) circuit is implemented. Until the VCC voltage has reached the POR threshold value, the internal reset is active, all operations are disabled and the device will not respond to any command. In the same way, when VCC drops down from the operating voltage to below the POR threshold value, all operations are disabled and the device will not respond to any command. A stable VCC must be applied before applying any logic signal.

Addressing:

The chip address of 24C02 comprises internal preset code nibble '1001' (binary) followed by internally configurable address pins/bits A2, A1 and A0. The eighth bit of the address byte is determined by the type of operation (either read or write) that is to be performed. For writing to the device the eight bit is '0' and for reading from the device the eighth bit is '1'. In our case, A2, A1 and A0 pins are grounded and hence the device address for writing is '1001000b' or 90 (hex) and for reading the device address is '10010001b' or 91 (hex).

Command Set:

Complete command instruction set for accessing various internal registers as well as for starting and stopping of conversion process are given in Table. For understanding the exact sequence in which start bit, address byte, acknowledgement bit, command byte and data bytes are to be sent along the I2C bus, please refer to the datasheet of 24C02, wherein these aspects have been explained in proper detail. This will help in understanding the contents of the main program.

Microcontroller Unit:

Microcontroller AT89C51 (IC2) is a 40 pin IC from Atmel. Its pin details are shown in the pin description diagram. Like AT89C51, it also belongs to the 8031/8051 family. Microcontroller AT89C52 has a 256*8 bit internal random- access memory (RAM), eight interrupt sources and 8KB of flash memory compared to 128*8 -bit internal RAM, six interrupt sources and 4KB flash memory in AT89C51. By combining a versatile 8-bit CPU with flash memory on a monolithic chip, Atmel AT89C51is a powerful, highly cost-effective solution to many embedded control applications. Ports 0 and 2 are 8-bit bidirectional input/ output (I/O) ports. These ports haven't been used in this temperature indicator. Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Ports 1.0 through 1.7 are connected to pins 7 through 14 of the LCD. Port 1 output buffers can sink/ source four TTl inputs. Port 3 is a 8-bit bidirectional I/O port with internal pull-ups. Ports 3.0 and 3.1 of IC2 are connected to serial clock line (SCL) and serial data line (SDA) of IC3, respectively. Port 3 output buffers can sink/source four TTL inputs. A 12MHz crystal oscillator is connected to XTAL1 and XTAL2 pins for operation of the microcontroller. A high pulse on RST pin (pin 9) while the oscillator is running resets the microcontroller. In this circuit, this pin is connected to +Vcc through capacitors C5 (10uF, 16V). The external-access enable pin (EA) is connected to +Vcc for internal program executions. This pin also receives the 12V programming enable voltage (Vpp) during flash programming when 12V program is selected

TESTING:

Visualization Test:
When the fabrication process is completed & all the components have been mounted perfectly the visualization testing is performed. In this testing the circuit is scanned simply by the eyes & not by the help of any instrument. It to ensure that the soldering is perfect and there is no loose connection between the components.

Pre-heating Test:
This test is performed to check the heat tolerance of the components. In this the circuit is provided power supply and left for some time. After a interval of time it is checked that if there is any component get faulty component specially for IC’s.

Program:

http://projects-applications.blogspot.com/2010/04/voting-machine-assembly.html

Component’s List for Project:
AT89C51 1
MAX 232 IC 1
IC 24C02 1
R S 232 Cable (Male, Female) 1
LED 2
Resistances 10K 2
Crystal Oscillator. (11.0592 MHz) 1
2 pin Switch 5
9- pin DB Connector 1
Diode 1n4007 4
IC Base (8Pin, 16 pin, 40Pin) 1 each
Power chord 1
Capacitor 1000Microfarad/ 25v 1
Capacitor 10 Microfarad / 25v 4
Voltage Regulator L7805CN 1
Transformer (9-0-9) 1