1. Microcontroller based Password Protected Home
Appliance
Authors Name Authors Name
Abhiraj Datta Saurabh Das
Arnab Debnath Suman Kalyan
Ronit Mondal Susmit Sarkar
Department of Electronics & Communication Engineering
Neotia Institute of Technology, Management & Science
Abstract— The microcontroller based digital lock is an access
control system that allows only authorized persons to access any
restricted division. The major components include a keypad,
LCD, EEPROM and the micro controller ATmega8A-PU which
belongs to the 8159 8-bit series of microcontrollers. The
electronic control assembly allows the system to unlock the device
with a password. A four digit predefined password needs to be
specified the user. A 4x4 matrix KEYPAD and a 16x2 LCD has
been used here to set the password which is stored in the
EEPROM so that we can change it at any time. While unlocking,
if the entered password from keypad matches with the stored
password, then the lock opens and a message is displayed on
LCD. Also an output pin is made high to be used for further
purpose. As the program starts, string ‘Enter Password’ is
displayed on LCD. If all the four digits match with set password,
LCD displays ‘password is correct’ and the lock output pin goes
high and the led glows. If the security code is wrong, ‘Wrong
Password’ is sent to be displayed on LCD and the buzzer rings
which is connected to the microcontroller.
I. INTRODUCTION
Security is a prime concern in our day-to-day life. Everyone
wants to be as much secure as possible. An access control for
appliances forms a vital link in a security chain. The
Microcontroller Based Password Protected Home Appliance is
an access control system that allows only authorized persons to
access an appliance. The system is fully controlled by the 8 bit
microcontroller ATmega8. There is a Keypad by which the
password can be entered through it. When they entered
password matches with the password stored in the memory
then we get access to the appliance.
II. BASIC BLOCK DIAGRAM
III. CIRCUIT EXPLANATION
The Main Part of the above Circuit diagram is the
Microcontroller ATmega8. The Keypad is the input device
and it is connected in a matrix format so that the numbers of
ports needed are reduced. The Microcontroller reads a four-
digit password through the Keypad. Then the Microcontroller
compares the four digit password with the number which is
pre-programmed and if it is equal then the Microcontroller
will switch on the motor for the appliance. The Password is
stored in the EEPROM and the password can be changed at
any time using the same keypad. The power supply section is
the important one. It should deliver constant output regulated
power supply 5V for successful working of the project. A 0-
12V/500 mA transformer is used for our purpose. The primary
of this transformer is connected in to main supply through
on/off switch & fuse for protecting from overload and short
circuit protection. The secondary is connected to the diodes
convert from 12V AC to 12V DC voltage which is further
regulated to +5v, by using IC 7805.

2. IV. HARDWARE DESIGN
 Microcontroller ATmega8A-PU
 LCD Display
 Relay Interface
 Buzzer
A. Microcontroller ATmega8A-PU
 High-performance, Low-power consumption with
Advanced RISC Architecture.
 High Endurance Non-volatile Memory segments.
a. 8KBytes of In-System Self-programmable Flash
program memory.
b.512Bytes EEPROM.
c. 1KByte Internal SRAM.
 Operating Voltages
a. 2.7 - 5.5V
b. 0 - 16MHz
 Power Consumption at 4MHz, 3V, 25°C
a. Active: 3.6mA
b.Idle Mode: 1.0mA
c. Power-down Mode: 0.5μA.
 Internal Calibrated RC Oscillator.
B. LCD display
The dot-matrix liquid crystal display controller and driver LSI
displays alphanumeric, characters, and symbols. It can be
configured to drive a dot-matrix liquid crystal display under the
control of a 4 or 8-bit microprocessor. Since all the functions
such as display RAM, character generator, and liquid crystal
driver, required for driving a dot-matrix liquid crystal display
are internally provided on one chip, a minimal system can be
interfaced with this controller/driver. A single HD44780U can
display up to two 8-character lines (16 x 2).A 16 x 2 line LCD
module to display user information. Micro controller send the
data signals through pin 11 through 18(RC0-RC3) and control
signal through 4,6 and 7 of the micro controller. Pin no 3 of the
LCD is used to control the contrast by using preset PR1.

C. Relay Interface
A single pole dabble throw (SPDT) relay is connected to
port RB1 of the microcontroller through a driver
transistor. The relay requires 12 volts at a current of
around 100ma, which cannot provide by the micro-
controller. So the driver transistor is added. The relay is
used to operate the external solenoid forming part of a
locking device or for operating any other electrical
devices. Normally the relay remains off. As soon as pin
of the microcontroller goes high, the relay operates.
When the relay operates and releases. Diode D2 is the
standard diode on a mechanical relay to prevent back
EMF from damaging Q3 when the relay releases. LED
L2 indicates relay on.
D. Buzzer
A buzzer connected to port RB0 of the micro controller
through a driver transistor. The buzzer requires 12 volts at
a current of around 50ma, which cannot provided by the
micro controller. So the driver transistor is added. The
buzzer is used to audible indication for valid user and error
situation and alarm mode. As soon as pin of the micro
controller goes high, the buzzer operates.

3. E. Keypad Interfacing
At the lowest level, keyboards are organized in a matrix of
rows and columns. The microcontroller accesses both rows and
column through ports; therefore, with two 8-bit ports, an 4*3
matrix of keys can be connected to a microprocessor. When a
key pressed, a row and column make a connect; otherwise,
there is no connection between row and column. In our project
the function of programs stored in the EEPROM of
microcontroller to scan the keys continuously, identify which
one has been activated, and present it to the microcontroller. In
this section we look at the mechanism by which the ATmega8
scans and identifies the key.
V. Abbreviations and Acronyms:
 EEPROM-Electrically Erasable Programmable Read
Only Memory.
 LCD- Liquid Crystal Display.
 RISC- Reduced instruction set computing.
 LED- Light Emitting Diode.
 SRAM- Static Random Access Memory.
VI. Acknowledgment
We are using this opportunity to express our gratitude to
everyone who supported us throughout the course of this
B.Tech final year project. We are thankful for their aspiring
guidance, invaluably constructive criticism and friendly advice
during the project work. We are sincerely grateful to them for
sharing their truthful and illuminating views on a number of
issues related to the project. We express our warm thanks to
our project mentors Prof. Biplob Roy and Prof. Amrita Saha
for their support and guidance at NITMAS.
VII. REFERENCES
1) Programming in ANSI C: E Balaguruswamy.
2) The 8051microcontroller & embedded systems: Muhammad Ali
Mazidi and Janice Gillispie Mazidi.
3) www.atmel.com
4) www.scientech.bz