A 4x3 matrix keypad and a 16x2 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.