Simple Electronic Lock using Keypad and 8051 microcontroller

There are several electronic devices which require a security lock for their protection. This article describes a way to build an electronic lock with a four-digit password. A keypad, interfaced with 8051 microcontroller (AT89C51), is used to enter the password. The password and its status are displayed on an LCD screen.

A 4×3 matrix keypad and a 16×2 LCD have been used here. Keypad and LCD are very commonly used input & output devices, respectively. A four digit predefined password is specified in the microcontroller AT89C51‘s program. If the entered password from keypad matches with this 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.

The connections in the circuit are as following: port P2 of microcontroller is used as data input port which is connected to data pins (7-14) of LCD. P1^0, P1^1 and P1^2 pins of microcontroller are connected to control pins RS, RW and EN of LCD. Port P0 is used to take input from keypad. P0^7 has been used as lock output pin of controller.

As the program starts, string ‘Enter Password’ is displayed on LCD. The keypad is scanned for pressed digits one by one. Every time row and column of the key pressed is detected and the resultant number is displayed on LCD. After the four digits are entered, they are compared with the pre-set password. If all the four digits match with set password, LCD displays ‘Lock Open’ and the lock output pin goes high. If the security code is wrong, ‘Wrong Password’ is sent to be displayed on LCD. The system gets locked if more than three attempts are made with wrong password to open the electronic lock. The system needs to be reset in such a case.

Project Source Code

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//Program to make a simple code lock. The default password is 3907.

#include<reg51.h>
#define port P1
#define dataport P2
#define key P0
#define sec 100
sbit rs = port^0;
sbit rw = port^1;
sbit en = port^2;

sbit col1=key^4;
sbit col2=key^5;
sbit col3=key^6;
sbit row1=key^0;
sbit row2=key^1;
sbit row3=key^2;
sbit row4=key^3;
sbit lock_output=P0^7;

int check=0;
int digit[4]={0,0,0,0};
int dig_one=3;
int dig_two=9;
int dig_three=0;
int dig_four=7;
int i,count=0;

void delay(unsigned int msec) //Time delay function
{
int i,j ;
for(i=0;i<msec;i++)
  for(j=0;j<1275;j++);
}

void lcd_cmd(unsigned char item) //Function to send command to LCD
{
dataport = item;
rs= 0;
rw=0;
en=1;
delay(1);
en=0;
return;
}

void lcd_data(unsigned char item) // Function to send data to LCD
{
dataport = item;
rs= 1;
rw=0;
en=1;
delay(1);
en=0;
return;
}

void lcd_data_string(unsigned char *str)  // Function to send string to LCD
{
int i=0;
while(str[i]!='')
{
  lcd_data(str[i]);
  i++;
  //delay(10);
}
return;
}

void lcd(unsigned char str[10])  // Function to send string to LCD
{
lcd_cmd(0x38);
lcd_cmd(0x0e);
lcd_data_string(str);
}

void ans()
{
if(check>3)
{
  lcd_cmd(0x01);
  lcd_cmd(0x82);
  lcd_data_string(" LOCK OPEN");
  lock_output=1;
  delay(500);
}
else
{
  lcd_cmd(0x01);
  lcd_cmd(0x82);
  lcd_data_string(" WRONG PASSWORD");
  lock_output=0;
  count++;
  delay(500);
}                   
}

void code_check() // Function to check password
{
if(i<=3 )
{
  switch((i+1))
  {
   case 1: {
      if(dig_one==digit[0])
      {
       check=check+1;
      }
      break;
     }

   case 2: {
      if(dig_two==digit[1])
      {
       check=check+1;
      }
      break;
     }
    
   case 3: {
      if(dig_three==digit[2])
      {
       check=check+1;
      }
      break;
      }
    
   case 4: {
      if(dig_four==digit[3])
      {
       check=check+1;
      }
      break;
     }
  }
}
if(i==3)
{
  ans();
}
}


void display(int a) //Display function
{
switch(a)
{ 
  case 1:{
    lcd_data('1');
    delay(30);
    digit[i]=1;
    code_check();
    break;
    }
  case 2:{
    lcd_data('2');
    delay(30);
    digit[i]=2;
    code_check(); 
    break;
    }
  case 3:{
    lcd_data('3');
    delay(30);
    digit[i]=3;
    code_check();
    break; 
    }
  case 4:{
    lcd_data('4');
    delay(30);
    digit[i]=4;
    code_check();
    break;
    }
  case 5:{
    lcd_data('5');
    delay(30);
    digit[i]=5;
    code_check();
    break;
    }
  case 6:{
    lcd_data('6');
    delay(30);
    digit[i]=6;
    code_check();
    break;
    }
  case 7:{
    lcd_data('7');
    delay(30);
    digit[i]=7;
    code_check();
    break;
    }
  case 8:{
    lcd_data('8');
    delay(30);
    digit[i]=8;
    code_check();
    break;
    }
  case 9:{
    lcd_data('9');
    delay(30);
    digit[i]=9;
    code_check();
    break;
    }
  case 0:{
    lcd_data('0');
    delay(30);
    digit[i]=0;
    code_check();
    break;
    }
}
}

void check_col1()
{
row1=row2=row3=row4=1;
row1=0;
if(col1==0)
display(1);
row1=1;
row2=0;
if(col1==0)
display(4);
row2=1;
row3=0;
if(col1==0)
display(7);
row3=1;
row4=0;
if(col1==0)
{
  row4=1;
}
}

void check_col2()
{
row1=row2=row3=row4=1;
row1=0;
if(col2==0)
display(2);
row1=1;
row2=0;
if(col2==0)
display(5);
row2=1;
row3=0;
if(col2==0)
display(8);
row3=1;
row4=0;
if(col2==0)
display(0);
row4=1;
}

void check_col3()
{
row1=row2=row3=row4=1;
row1=0;
if(col3==0)
display(3);
row1=1;
row2=0;
if(col3==0)
display(6);
row2=1;
row3=0;
if(col3==0)
display(9);
row3=1;
row4=0;
if(col3==0)
{
  row4=1;
}
}

void main()
{
col1=col2=col3=1;
while(1)
{
  lcd_cmd(0x01);  //Clear LCD screen
  lock_output=0;
  lcd_cmd(0x82);   // Set cursor on position first of first line
  lcd("ENTER PASSWORD");
  check=0;
  row1=row2=row3=row4=0;
  while(col1==1 && col2==1 && col3==1);
  for(i=0;i<4;i++)
  {
   delay(100);
   lcd_cmd(0xc4+i);
   row1=row2=row3=row4=0;
   while(col1==1 && col2==1 && col3==1);
   row1=row2=row3=row4=0;
   if(col1==0)
   check_col1();
   else
    if(col2==0)
    check_col2();
    else
     if(col3==0)
     check_col3();
   if(count==4)
   {
   lcd_cmd(0x01);
   lcd_cmd(0x86);
   lcd("SORRY");
   lcd_cmd(0xc1);
   lcd("NO MORE TRIALS");
   while(1);
   }
  }   
}
}
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