automatic door locking system

8/18/2019 Automatic Door Locking System

1/32

CE00626-2 Digital and Embedded software(Real time system)-2 Individual Assignment Page 1 of 32

Level 2 Asia Pacific Institute of Information Technology 2015

1. Introduction

1.1 Objective

The objective of this project is to implement a password based door locking system by using the

microcontroller 68hc11/8051/8086 and to integrate the hardware and software in order to

simulate the functions of the above system. The microcontroller based Door locking system is an

access control system that allows only authorized persons to access a restricted area. The

password is stored in the EEPROM so that we can change it any time. The system has a 4×3

keypad which is used to enter the Password. A 16×2 LCD is also used to display the password

entered. If the entered password is correct then the system opens the door by rotating the door

motor. If the password is wrong then the door will remain closed and an alarm will be generated to detect an unauthorized entry of a person.

1.2 What is password based door locking system?

It is a microcontroller based system designed to restrict unauthorized entry. A predefined

password is fed in the microcontroller. To enter the password, a 4×3 Keypad is connected to the

system and to display the password entered, a 16×2 LCD is used. They system is fixed at the

entry door to control a solenoid operated lock with the help of a motor. When an authorized person enters the predefined password via keypad, the motor is operated for a limited time to

unlatch solenoid operated door so the door can be open. At the end of preset delay, the motor is

operated in reverse direction and the door gets locked again. When the password has been

incorrectly entered the buzzer gives a chirping sound.

The system is totally designed using embedded systems technology. The controlling unit has an

application program to allow the microcontroller read the incoming data and control the motor.

The project uses AT89C51 microcontroller as the control unit (Reddy,2011).

1.3 Need for password protected door locking system

Today, security has become increasing concern. An access control for doors forms a vital link in

a security chain. The microcontroller based digital lock for Doors is an access control system that

allows only authorized persons to enter in a restricted area viz. military base, research centre.


2/32



Moreover it can be implemented in homes. We often forget to carry door key. It is really difficult

to get inside the house. In offices security personnel checks the I-card of the employees to

restrict unauthorized entry or the employees sign a register before entrance. But if there are

multiple entry points it is not feasible to arrange security personnel at each gate as wells as it

would not be cost effective. This project solves these problems and is a substitute for bar code

recognition system, punch card system (Reddy,2011).


3/32



2. Working principle and detailed theory

2.1 Block diagram description

The block diagram consists of a Microcontroller, a 16×2 LCD, a 4×3 keypad, Motor driver IC(L293D) connected to a DC motor and a buzzer. Each of these block are described below2.1.1

2.2.1 Microcontroller

This is control unit of our system. In this project microcontroller of 8051 family is used. The

microcontroller is used to:

i. Read the digital input provided by keypad

ii. Display the entered password on LCD

iii. Match the password entered with that of predefined password

iv. Rotate the motor if password matches else send logic to complete buzzer circuit for

an alarming sound

AT89C51 of 8051 family is used in this project.

Figure 1: Block diagram of circuit


4/32



AT89C51 (Microcontroller)

This module comprises 8051 microcontroller (AT89C51). It belongs to Atmel family. Atmel

89C51 have flash programmable and erasable read only memory (PEROM). Flash memory is a

non volatile memory, which can be electrically erased read for lines and blocks. The mechanismfor erasing the memory is easier and faster than that needed for EEPROM. Typically, 1000

write/erase cycles are possible, which are more than sufficient for any application development.

The operating frequency of 89C51 could be from 0Hz to 24Hz.

Architectural overview of ATMEL89C51

Atmel AT89C51 is a powerful microcontroller which provides a highly flexible and cost

effective solution to many embedded control applications. Since AT89C51 architecture provides

32 bidirectional port pins along with two timers and 4Kbytes of flash memory, it makes the

choice ideal for the system is an RTC chip DS1307 from Dallas semiconductors, which

continuously updates the time and calendar information in its scratch pad RAM, considering leap

year compensation. Stability and accuracy of the clock is dependent on the accuracy of the clock

as well as matching of the capacitance between crystal oscillator and clock pins. There are two

16-bit timer/counters, one full duplex serial port, 128 bytes of on chip RAM, 32I/O lines, on chip

oscillator and clock circuitry. It support six interrupt sources. It consists of precision analog

comparator. It must be noted that pin P3.6 is not available externally; however it can be read in

software. P3.6 is the output of precision analog comparator

Atmel series AT89C51 is based on Harvard architecture. This processor includes internal

separated data memory (internal RAM) and program memory (internal Flash). It is possible to

connect external data memory and external program memory as well through I/O ports P0 and

P2 and control signals (detailed connection will be discussed later). Internal data memory and

program memory are separated into two different areas and are accessed at the same time via

data transfer instruction (like MOV A, 20H). External data and program memory shares the same

address and data bus, thus advantage of Harvard Design of Electronic Instruments Embedded

systems for industrial control 23 architecture is not utilized. But external data access instruction

(like MOVX A, @DPTR) and external program access instruction (MOVC A, @DPTR) still

differs (Soni,2010).


5/32



Pin Description of 8051

The 8051 is packaged in a 40-pin DIP (Dual Inline Package). Many pins of 8051 are used for

more than one function.

Port 0 (Pins 32-39)

Port 0 pins can be used as I/O pins. The output drives and input buffers of port 0 are used to

access external memory. Port 0 outputs the low order byte of external memory address, time

multiplexed with the data being written or read. Thus, port 0 can be used as a multiplexed

address/data bus.

Port 1 (Pins 1-8)

Port 1 pins can be used only as I/O ports. This port does not need any pull-up resistors since it

already has pull up resistors internally. Upon reset, port 1 is configures as an input port.

Figure 2: Pin Out of 8051


6/32



Port 2 (Pins 21-28)

The output drives of port 2 are used to access external memory. Port 2 outputs the high order

byte of the external memory address when the address is a6=bits wide. Otherwise, port 2 is used

as an I/O port.

Port 3 (Pins 10-17)

All port pins of port 3 are multifunctional. They have special functions as shown below including

two external interrupts, two counter inputs, two special data lines and two timing control strobes.

Table 1: Pin description

Symbol Position Name and significance

RD P3.7 Read data control output. Active low pulse generated by hardware whenexternal data memory is read.

WR P3.7 Write data control output. Active low pulse generated by hardware whenexternal data memory is written.T1 P3.5 Timer/counter 1 external input or test pin.T0 P3.4 Timer/counter 0 external input or test pin.

INT1 P3.3 Interrupt 1 input pin. Low level or falling edge triggered.

INT0 P3.2 Interrupt 0 input pin. Low level or falling edge triggered.

TXD P3.1 Transmit data pin for serial port in UART mode. Clock output in shift

register mode.RXD P3.0 Receive data pin for serial port in UART mode. Data I/O pin in shiftregister mode.

Power supply pins V CC (Pin 40) and V SS (Pin 20)

8051 operates on d.c. power supply of +5V with respect to ground. The +5V is to be connected

to pins V CC and ground to pin V CC with rated power supply current of 125mA.

Oscillator pins XTAL (Pins 18 and 19)

For generating an internal clock signal, the external oscillator is connected at these two pins.

ALE (Address Latch Enable, Pin 30)

AD0 to AD7 lines are multiplexed. To demultiplex these lines and for obtaining lower half of an

address, an external latch and ALE signal of 8051 is used.


7/32



RESET (Pin 9)

This pin is used to reset 8051. For proper reset operation, reset signal must be held high at least

for two machine cycles, while oscillator is running.

PSEN (Program Store Enable, Pin 29)

It is the active low output control signal used to activate the enable signal of the external

ROM/EPROM. It is activated every six oscillator periods while reading the external memory.

Thus, this signal acts as the read strobe to external program memory.

EA (External Access, Pin 31)

When the EA pin is high (connected to V CC), program fetches to address 0000H through 0FFFh

are directed to the internal ROM and program fetches to address 1000H through FFFFH are

directed to external ROM/EPROM. When EA is low (grounded), all addresses (0000H to

FFFFH) fetched by program are directed to the external ROM/EPROM.

2.1.2 LCD

A 16×2 LCD (Liquid Crystal display) is used to display the password entered. It is an electronics

display module and find a wide range of applications. The module is preferred over seven

segment display and other multi segment display LEDs. The reason being: LCDs are

economical, easily programmable, have no limitation of displaying special and even custom

characters (unlike in seven segments).

A 16×2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD

each character is displayed in 5×7 pixel matrix. This LCD has the registers namely command and

data.

The command register stores the command instructions given to the LCD. A command is an

instruction given to LCD to do a predefined task like initializing it, clearing screen, setting the

cursor position, controlling display etc. the data register stores the data to be displayed on the

LCD. The data is the ASCII value of the character to be displayed on the LCD. PIN description

of 16×2 LCD is shown in table below:


8/32



Table 2: Pin description of LCD

PinNo

Function Name

1 Ground (0V) Ground 2 Supply voltage; 5V (4.7V – 5.3V) Vcc 3 Contrast adjustment; through a variable resistor VEE

4 Selects command register when low; and data register when high Register Select

5 Low to write to the register; High to read from the register Read/write 6 Sends data to data pins when a high to low pulse is given Enable 7

8-bit data pins

DB0 8 DB1 9 DB2

10 DB3 11 DB4

12 DB5 13 DB6 14 DB7 15 Backlight V CC (5V) Led+ 16 Backlight Ground (0V) Led-

Figure 3: LCD Pin Out


9/32



2.1.3 Keypad

The 4×3 keypad contains push buttons that are arranged in four rows and three columns produce

twelve characters as shown in the figure below. It is made of thin, flexible membrane material

with an adhesive backing. The keys are connected into a matrix, so that we need 7microcontroller pins (3columns and 4 rows) to scan through the pad. It is used to enter the

password in this project.

2.1.4 Motor Driver IC

Microcontroller operates at low voltages and require small amount of current to operate while the

motor requires a relatively higher voltages and current. This current cannot be supplied to the

motors from the microcontroller. That is why motor driver IC is used in this system.

The IC L293D is a dual H bridge IC which also provides sufficient current to drive a small

motor. It’s Pin configuration is shown below . With one such IC DC motors can be driven which

can be controlled in both clockwise and counter clockwise directions. For the applications that

don’t need reversal of direction, the four output pins can be used for driving four separate

motors. This IC is rated for an output current of 600mA and peak output current of 1.2A per

channel. Moreover for protection of this circuit against back EMF, snubber/flywheel diodes are

included within the IC (Das,1995).

Figure 4: L293D IC


10/32



2.1.5 DC motor

A DC motor is used so that it can be further connected to solenoid to open the door.

A DC motor in simple words is a device that converts direct current (electrical energy) into

mechanical energy.

2.1.6 Buzzer

We are using a buzzer as an alarm to indicate the wrong password to open the door.

2.1.7 LM7805 (Voltage regulator)

The LM7805 monolithic 3-terminal positive voltage regulator employ internal current limiting,

thermal shutdown and safe area compensation, making them essentially indestructible. If

adequate heat sinking is provided, they can deliver over 1.0A output current. They are intended

as fixed voltage regulators in a wide range of applications including local regulation for

elimination of noise and distribution problems associated with single point regulation. In

addition to use as fixed voltage regulators, these devices can be used with external components

to obtain adjustable output voltages and currents. Considerable effort was expended to make the

entire series of regulators easy to use and minimize the number of external components. It is not

necessary to bypass the output, although this does improve transient response. Input bypassing is

needed only if the regulator is located far from the filter capacitor of power supply

(Mathew,2011).

Figure 5: LM7805 IC


11/32



3. Circuit design

3.1 Working Principle

The circuit operates on the principle of microcontroller interfacing. A keypad interfaced to themicrocontroller is used to enter the password and store it. A LCD is interfaced to the

microcontroller to display the status and a motor is interfaced to the microcontroller via the

motor driver. The motor is first rotated forward to open the gate and then backward to close the

gate.

3.2 Circuit Explanation

The main part of the above circuit diagram is the Microcontroller AT89C51. The keypad is the

input device and it is connected in a Matrix format so that the numbers of port needed are

reduced. The Microcontroller reads a four digit password through the Keypad. Then the

Microcontroller compares the four digit password with the password which is pre-programmed

Figure 6: Circuit design in Proteus


12/32



and if it is equal then the Microcontroller will switch on the motor for the door and if we enter

the wrong password then an alarm will be switched on.

The password is stored in the EEPROM and the password can be changed by making changes in

program. The power supply section is the important one. It should deliver constant output

regulated power supply for successful working of the project. A 9V transistor battery is used as

power supply, which is further regulated to 5V, by using IC 7805.

Reset circuit design: The reset pin of the microcontroller is kept active till the power supply is in

specified range and minimum oscillation level is maintained. In other words to ensure the supply

voltage doesn’t falls below the threshold level of 1.2V and the reset pulse width is greater than

100ms (for AT89C51), we select the values of resistor and capacitor such that RC ≥100ms. Here

we select 8.2K ohm resistor and a 10µF electrolyte capacitor.

Oscillator circuit design: A crystal oscillator is used to provide external clock signal of 24MHzto the microcontroller. To forward the clock cycle in only one direction, we connect two ceramic

capacitors each of 33µF. this crystal oscillator is connected between pin 18 and 19 of the

microcontroller.

Microcontroller interfacing design: A 4×3 keypad is interfaced to the microcontroller Port1

and a motor driver IC (L293D) is interfaced to microcontroller port pins P3.0 and P3.1. An LCD

is interfaced to the microcontroller such that the register select, read/write and enable pins are

connected to port pins P3.6, P3.7 and P3.8 respectively whereas the data pins are connected to

Port2.

Circuit design in Proteus: Circuit is designed and then simulated in Proteus.

Compilation of Microcontroller code: Once the circuit is designed and drawn on a piece of

paper, the next step is to write and compile the code. Here we select the keil µvision software to

write the program in C language.

Prior to writing the code, the general steps needed to be followed like creating a new project and

selecting the target device or the required microcontroller. Once the code is written, we saved it

with .c extension and then added it to the source file group under the target folder. The code is

then compiled by pressing F7key.

Once the code is compiled, a hex file is created. In the next step, we use Proteus software to draw

the circuit. The code is dumped into the microcontroller by tight click on the same and then


13/32



adding the hex file. The microcontroller oscillating frequency is selected here to be

11.0592MHz.

Once the circuit is powered, microcontroller sends commands to the LCD such that it is ready to

accept the data. This data is entered using the keypad. Once the data is entered, it is displayed on

the LCD. This data denotes the password. The password is entered using the keypad and it is

checked with the set password. If the passwords match, the microcontroller sends signals to the

motor driver such that pin P3.0 is at high level and pin P3.1 is at low level and the motor rotates

in forward direction. After a certain delay, the enable pin is grounded by sending a low logic

signal from the microcontroller and the motor stops. Again after some time delay, the

microcontroller sends signals to the motor driver such that P3.0 is at low logic level, P3.1 is ate

logic high level. The motor now rotates in backward direction. Now if the passwords do not

match, the microcontroller sends a logic low signal to the enable pin of the microcontroller, thusdisabling the motor driver and the motor does not rotates at all. The buzzer connected to the

pin1.7 gets logic high level and an alarming sound is heard that indicates wrong password.

3.3 Program

/*Password protected door locking system by Pankaj kumar*/

/*default password is 12345*/

#include#include

#define lcdport P2

/*variable declaration of port pins using sbit*/

sbit rs=P3^4;

sbit rw=P3^5;

sbit en=P3^6;

sbit m1=P3^0;

sbit m2=P3^1;

sbit r1=P1^0;

sbit r2=P1^1;

sbit r3=P1^2;

sbit r4=P1^3;


14/32



sbit c1=P1^4;

sbit c2=P1^5;

sbit c3=P1^6;

sbit buzzer=P1^7;

/*Function declaration with data type*/

char uid[]="12345";

char id[5];

void lcdint();

void user_id(char);

void lcdstring(char *);

void delay(int);

void lcdcmd(char);void lcddata(char);

void check_id();

char scankey();

char check();

void door_open();

void door_close();

void sounder();

/*Main Program*/

void main()

{

int n; //defining variable “n” as integer

char key; //defining variable “key” as character

P2=0x00; //Making Port2 as output port

P1=0xff; //Making Port1 as input port

buzzer=1;

lcdint();

lcdstring("system is locked");

lcdcmd(0xc0);

lcdstring("enter user id");


15/32



delay(100); //delay of 100ms

lcdcmd(0x01);

lcdcmd(0x02);

lcdstring("user_id");

lcdcmd(0xc0);

n=0; //Initializing the value of integer

while(n


16/32



lcdcmd(0x01);

lcdcmd(0x02);

}

}

/*Function definition for buzzer*/

void sounder()

{

int i;

for(i=0;i


17/32



m1=1;

m2=0;

m1=0;

m2=1;

delay(400);

m1=0;

m2=0;

}

/*Function definition to check authenticity of pre programmed password*/

char check()

{

char b='a';while(b=='a')

{

b=scankey();

}

return b;

}

char scankey()

{

c1=c2=c3=1;

r1=r2=r3=r4=0;

r1=0;r2=r3=r4=1;

if(c1==0)

{

delay(2);

return '1';

}

if(c2==0)

{

delay(2);


18/32



return '2';

}

if(c3==0)

{

delay(2);

return '3';

}

r2=0;r1=r3=r4=1;

if(c1==0)

{

delay(2);

return '4';}

if(c2==0)

{

delay(2);

return '5';

}

if(c3==0)

{

delay(2);

return '6';

}

r3=0;r1=r2=r4=1;

if(c1==0)

{

delay(2);

return '7';

}

if(c2==0)

{


19/32



delay(2);

return '8';

}

if(c3==0)

{

delay(2);

return '9';

}

r4=0;r1=r2=r3=1;

if(c1==0)

{

delay(2);return '*';

}

if(c2==0)

{

delay(2);

return '0';

}

if(c3==0)

{

delay(2);

return '#';

}

return 'a';

}

void lcdstring(char *p)

{

while(*p!='\0')

{

lcddata(*p);


20/32


21/32



}

void lcddata(char value)

{

lcdport=value;

rs=1;

rw=0;

en=1;

delay(1);

en=0;

}


22/32



4. Results

4.1 Screen shots of keil and Proteus window

Figure 7: Change in Port pin values

Figure 8: Keil window of program compilation


23/32



Figure 9: Change in Register values


24/32



The circuit is simulated in Proteus. The LCD displays “user_id” text indicates the user to enter

password. The two red dots on Pin 2 & 7 of Motor driver IC (L293D) in the figure below shows

that motor is not rotating. The two pins of buzzer having red dots indicating both are at high

signal (Buzzer not working as both terminals are getting high signal logic).

Figure 10: Circuit while simulation


25/32



The pre- programmed password i.e. “12345” is entered through keypad. The LCD displays the

message “id matched”.

Figure 11: Password matched


26/32



Here we can notice the color of dots of pins of IC changes indicating that one pin is getting high

voltage and second is getting low voltage. This shows that motor is rotating but still the buzzer is

off.

Figure 12: Motor is ON, Buzzer is OFF


27/32



Again user enters the password, but this time the password is unmatched. This time the pins of

Buzzer get both high and low voltage which results in an alarming sound. The LCD displays the

message “try again” to reenter the password.

Figure 13: Unmatched Password


28/32



4.2 Hardware Circuit

Figure 15: Motor spinning with message opening door

Figure 14: Hardware circuit showing message “User ID”


29/32



Figure 16: Motor spinning with message closing door

Figure 17: Wrong password with message “ try again"


30/32



5. Conclusion

The goal of this project was to build a password protected door locking system. The goal was

successfully achieved. The circuit was designed in Proteus. The program for this system was

written in c language. Then this program was compiled in Keil µvision. After compilation, hex

file was created. This hex file was dumped to microcontroller in Proteus and the circuit was

simulated. The pre-programmed password was entered using keypad. If the password matches

the pre programmed password the motor rotates else it gives an alarming sound. The default

password is “12345”. The same circuit was build on a copper PCB.

5.1 Limitations

It is battery operated circuit and can easily run out of power once the battery life timeends.

It is a low range circuit, i.e. it is not possible to operate the circuit remotely.

5.2 Applications

The term access control refers to the practice of restricting entrance to a property, a building or a

room to authorized persons. Integrated and controller based access control numeric and

alphabetic keyless entry keypads with programmable features for the access control of singleopenings. The various applications are as follows:

Industrial facilities Commercial building Research centre Airports Psychiatrist care centres

Military base Drug rehabilitation centre

5.3 Future Enhancement

Electrical device such as lights, computers etc. can be controlled by using separate

passwords.


31/32



The system can be easily connected to the personal computer for further control Other than the speaker sounds, all the lights are made to turned on if password entered is

wrong and also hidden camera is used to record the faces who trespassed.

We can use this system as an attendance register for the students to enter a classroom

with their respective password. We can send this data to a remote location using mobile

or internet.


32/32


6. References

1. Electronics Hub (2014) Password Based Door Lock System using 8051 Microcontroller .

[Online] Available from: http://www.electronicshub.org/password-based-door-lock-

system-using-8051-microcontroller/ [Accessed: 4/04/2015]

2. Free Microcontroller Project (2013) Free Microcontroller Project . [Online] Available

from: http://www.8051projects.info/proj.asp?ID=68 [Accessed:5/04/2015]

3. Ghoshal, S. (2009) Embedded Systems & Robots: Projects Using The 8051

Microcontroller. New York: Delmar Learning.

4. Ibrahim, D. (2000) Microcontroller projects in C for the 8051. Oxford: Newnes.

5. Kaur, I. (2010) Microcontroller based home automation system with security.

International Journal of Advanced Computer Science and Applications. 1(6). p.60-65.6. Mazidi, M. A., Mazidi, J. G., & McKinlay, R. D. (2006) The 8051 microcontroller and

embedded systems: using Assembly and C (Vol. 626). New Jersey: Pearson/Prentice Hall.

7. Pandey, N. (2014) Electronics Projects Vol 24. New Delhi: EFY Enterprises Pvt. Ltd.

p.36-37.

8. Pont, M. J. (2002) Embedded C. Boston: Addison-Wesley Longman Publishing Co., Inc.

9. Predko, M. (1999) Programming and customizing the 8051 microcontroller . New York:

McGraw-Hill.

10. Reddy,A. & Chander,A. (2011) Digital Security Code using 8051 Microcontroller.

GRIET journal . 1(1). p.7-8.

11. Soni.H(2010) Proceedings of the 2009 International conference on signals, systems and

automation. [Online] Delhi: Universal Publishers. Available from: https://

books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51 +is+a+

powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solut

ion+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uA

TgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%2

0powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20a

nd%20cost%20effective%20solution%20to%20many%20embedded%20control%20appli

cations.&f=false . [Accessed: 28/03/2015]
http://www.electronicshub.org/password-based-door-lock-system-using-8051-microcontroller/http://www.electronicshub.org/password-based-door-lock-system-using-8051-microcontroller/http://www.8051projects.info/proj.asp?ID=68https://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttps://books.google.co.in/books?id=dJ3EqEZslGQC&pg=PA133&dq=Atmel+AT89C51+is+a+powerful+microcontroller+which+provides+a+highly+flexible+and+cost+effective+solution+to+many+embedded+control+applications.&hl=en&sa=X&ei=ZwkyVeaBNcm5uATgnICABg&ved=0CCYQ6AEwAA#v=onepage&q=Atmel%20AT89C51%20is%20a%20powerful%20microcontroller%20which%20provides%20a%20highly%20flexible%20and%20cost%20effective%20solution%20to%20many%20embedded%20control%20applications.&f=falsehttp://www.8051projects.info/proj.asp?ID=68http://www.electronicshub.org/password-based-door-lock-system-using-8051-microcontroller/http://www.electronicshub.org/password-based-door-lock-system-using-8051-microcontroller/

automatic door locking system

Documents