Password
based automatic door lock
Security is a prime concern in our day-today life.
Everyone wants to be as much secure as possible. An electronic lock allows
activation of an electric appliance only on entering the correct password. This
is also such an electronic locking system in which PIC16F887A microcontroller
plays the role of the central processing unit. The MCU is interfaced with a 4×4 matrix keypad and a
16×2 LCD to form the user interface.
The job of the MCU in this project is to receive
signals from the input device (keypad) and take corresponding actions. Whenever
any key is pressed on the keypad, the software program in the MCU identifies
the pressed key and accordingly turns on or turns off the appliance.
Simultaneously, it also displays a message on the LCD screen. The system turns
on the appliance on entering a four digit password set by the user and displays
message “password accepted” on LCD screen for 2 seconds followed by the message
“lock open”. If the entered password is not correct then the message “lock
denied” should be displayed on LCD screen for 2 seconds and followed by the
message “lock closed”.
The user can also change the password by using
corresponding key. Using this circuit any electrical appliance can be made as
password protected. It can also be used as an electronic door lock by
interfacing the output of the circuit with an electrically actuated door lock.
Block
diagram
Block
diagram description
The circuit
is based on PIC micro controller. It can be divided into five sections: input
(4×4 matrix keypad), processing unit (PIC16F877A MCU), appliance controller
(relay driver), display (16×2 LCD), and power supply. The PIC16F877A is an
8-bit micro controller. It has 8k×14-bit flash program memory, 368 bytes of RAM
and many other internal peripherals like analogue-to-digital converter, USART,
timers, synchronous serial port, compare captures and pulse width modulation
modules, EEPROM and analogue comparators. The job of the MCU in this project is
to receive signals from the input device (keypad) and take corresponding
actions. Whenever any key is pressed on the keypad, the software program in the
MCU identifies the pressed key and accordingly turns on or turns off the
appliance. Simultaneously, it also displays a message on the LCD screen.
Matrix keypad
A 4×4 matrix keypad is
used to give commands and the password to the MCU. It consists of 16 keys
arranged in the form of a square matrix of four rows and four columns. Each key
in the matrix is labeled according to the operation assigned to it.
LCD
A 16×2 LCD is
used to display various messages. It also displays an asterisk mark (*) for
each digit of the password entered. Control lines EN, RW and RS of the LCD
module are connected to pins RA1, RA2 and RA3 of Port A of the MCU,
respectively. Commands and the data to be displayed are sent to the LCD module
in nibble mode from Port D of the MCU. The higher four data bits of the LCD (D4
through D7) are connected to the lower nibble of Port D (RD0 through RD3) of
the microcontroller.
Relay driver
RC2
pin of Port C of the microcontroller is interfaced with the relay driver
circuit to switch on or switch off the AC load (appliance). A relay driver
circuit is nothing but a simple electronic circuit that drives an
electromechanical relay. In this project, a 6V, single-changeover relay is used
for switching the appliance ‘on’ or ‘off.’ Whenever the user enters the correct
password, RC2 pin goes high. The relay energies and the appliance turn ‘on.’
When RC2 is low, the appliance turns ‘off.’ Free-wheeling diode 1N4007 protects
the relay driver circuit from the reverse voltage developed in the relay coil.
Power supply
The 230V AC mains supply is stepped down to 9V AC
using step-down transformer X1. The output from the secondary of the
transformer is rectified by a bridge rectifier and filtered by capacitor. The
filtered output is regulated by ICs to obtain the required 5V and 6V,
respectively.
Circuit Diagram
Relay Driver Circuit
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