17-07-2013, 02:46 PM
Electronic code lock with user defined password using 8051 microcontroller (AT89C51)
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INTRODUCTION
An electronic lock is a device which has an electronic control assembly attached to it. They are provided with an access control system. This system allows the user to unlock the device with a password. The password is entered by making use of a keypad. The user can also set his password to ensure better protection. The major components include a keypad, LCD and the controller AT89C51 which belongs to the 8051series of microcontrollers. This article describes the making of an electronic code lock using the 8051 microcontroller.
A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers.
1. Command/Instruction Register- stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing, clearing the screen, setting the cursor position, controlling display etc.
2. 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.
Programming the LCD:
1. Data pin8 (DB7) of the LCD is busy flag and is read when R/W = 1 & RS = 0. When busy flag=1, it means that LCD is not ready to accept data since it is busy with the internal operations. Therefore before passing any data to LCD, its command register should be read and busy flag should be checked.
2. To send data on the LCD, data is first written to the data pins with R/W = 0 (to specify the write operation) and RS = 1 (to select the data register). A high to low pulse is given at EN pin when data is sent. Each write operation is performed on the positive edge of the Enable signal.
3. To send a command on the LCD, a particular command is first specified to the data pins with R/W = 0 (to specify the write operation) and RS = 0 (to select the command register). A high to low pulse is given at EN pin when data is sent.
Displaying single character ‘A’ on LCD
The LCD is interfaced with microcontroller (AT89C51). This microcontroller has 40 pins with four 8-bit ports (P0, P1, P2, and P3). Here P1 is used as output port which is connected to data pins of the LCD. The control pins (pin 4-6) are controlled by pins 2-4 of P0 port. Pin 3 is connected to a preset of 10k? to adjust the contrast on LCD screen. This program uses the above concepts of interfacing the LCD with controller by displaying the character ‘A’ on it.