Introduction
A digital code lock system is a secure and efficient way to control access to restricted areas or devices. This system uses a keypad for inputting a code, a microcontroller to process the input, and an output device (like an electric lock or a solenoid) to indicate whether the code entered is correct. This article explains the design and implementation of a digital code lock using the 8051 microcontroller.
Components Required
8051 Microcontroller
4x4 Keypad
16x2 LCD Display
Relay Module or Solenoid Lock
Power Supply
Connecting Wires
Resistors, Capacitors, and other passive components
System Overview
The digital code lock system consists of a 4x4 keypad for inputting the code, an LCD to display the status, and a relay module to control the lock mechanism. The 8051 microcontroller interfaces with the keypad to read the input code, compares it with the predefined code, and controls the relay based on the result.
Circuit Diagram
Digital Code Lock System Circuit Diagram:
Note: Add the circuit diagram image as described above.
Working Principle
Keypad Interface:
The 4x4 keypad is connected to the microcontroller's input ports.
Each key press generates a unique combination of row and column signals.
Code Verification:
The microcontroller reads the key pressed and stores the input.
Once the complete code is entered, the microcontroller compares it with the predefined code.
Output Control:
If the entered code matches the predefined code, the microcontroller activates the relay to unlock the door.
The status (correct or incorrect code) is displayed on the LCD.
Circuit Design
1. Keypad Interface:
Connect the rows of the 4x4 keypad to one set of the microcontroller's input pins.
Connect the columns of the keypad to another set of the microcontroller's input pins.
2. LCD Display Interface:
Connect the data pins of the LCD to the designated ports of the 8051 microcontroller.
Connect the control pins (RS, RW, E) of the LCD to the appropriate microcontroller pins.
3. Relay Module Interface:
Connect the control pin of the relay module to one of the digital output pins of the microcontroller.
Programming the 8051 Microcontroller
The program for the 8051 microcontroller is written in Embedded C. It involves initializing the keypad and LCD, reading the keypad inputs, verifying the code, and controlling the relay.
Code:
#include <reg51.h>// Define connectionssbit RS = P2^0;sbit RW = P2^1;sbit EN = P2^2;sfr LCD_DATA = 0xA0; // LCD data portsbit RELAY = P2^3;// Define keypad connectionssbit R1 = P1^0;sbit R2 = P1^1;sbit R3 = P1^2;sbit R4 = P1^3;sbit C1 = P1^4;sbit C2 = P1^5;sbit C3 = P1^6;sbit C4 = P1^7;unsigned char code[] = "1234"; // Predefined codeunsigned char input[5];unsigned char i = 0;void delay(unsigned int ms) { unsigned int i, j; for(i = 0; i < ms; i++) { for(j = 0; j < 1275; j++); }}void lcd_cmd(unsigned char cmd) { LCD_DATA = cmd; RS = 0; RW = 0; EN = 1; delay(1); EN = 0;}void lcd_data(unsigned char data) { LCD_DATA = data; RS = 1; RW = 0; EN = 1; delay(1); EN = 0;}void lcd_init() { lcd_cmd(0x38); // 2 lines, 5x7 matrix lcd_cmd(0x0C); // Display on, cursor off lcd_cmd(0x06); // Increment cursor lcd_cmd(0x01); // Clear display}void lcd_string(unsigned char *str) { while(*str) { lcd_data(*str++); }}unsigned char read_keypad() { C1 = 1; C2 = 1; C3 = 1; C4 = 1; R1 = 0; R2 = 1; R3 = 1; R4 = 1; if(C1 == 0) { delay(100); while(C1 == 0); return '1'; } if(C2 == 0) { delay(100); while(C2 == 0); return '2'; } if(C3 == 0) { delay(100); while(C3 == 0); return '3'; } if(C4 == 0) { delay(100); while(C4 == 0); return 'A'; } R1 = 1; R2 = 0; R3 = 1; R4 = 1; if(C1 == 0) { delay(100); while(C1 == 0); return '4'; } if(C2 == 0) { delay(100); while(C2 == 0); return '5'; } if(C3 == 0) { delay(100); while(C3 == 0); return '6'; } if(C4 == 0) { delay(100); while(C4 == 0); return 'B'; } R1 = 1; R2 = 1; R3 = 0; R4 = 1; if(C1 == 0) { delay(100); while(C1 == 0); return '7'; } if(C2 == 0) { delay(100); while(C2 == 0); return '8'; } if(C3 == 0) { delay(100); while(C3 == 0); return '9'; } if(C4 == 0) { delay(100); while(C4 == 0); return 'C'; } R1 = 1; R2 = 1; R3 = 1; R4 = 0; if(C1 == 0) { delay(100); while(C1 == 0); return '*'; } if(C2 == 0) { delay(100); while(C2 == 0); return '0'; } if(C3 == 0) { delay(100); while(C3 == 0); return '#'; } if(C4 == 0) { delay(100); while(C4 == 0); return 'D'; } return '\0'; // No key pressed}void main() { unsigned char key; lcd_init(); lcd_cmd(0x80); // Move to first line lcd_string("Enter Code:"); while(1) { key = read_keypad(); if(key != '\0') { lcd_cmd(0xC0); // Move to second line lcd_data(key); input[i++] = key; if(i == 4) { input[i] = '\0'; // Null-terminate the string i = 0; // Reset the index if(strcmp(input, code) == 0) { lcd_cmd(0x01); // Clear display lcd_string("Correct Code!"); RELAY = 1; // Activate relay to unlock delay(5000); // Keep the relay on for 5 seconds RELAY = 0; // Deactivate relay lcd_cmd(0x01); // Clear display lcd_cmd(0x80); // Move to first line lcd_string("Enter Code:"); } else { lcd_cmd(0x01); // Clear display lcd_string("Incorrect Code!"); delay(2000); // Display the message for 2 seconds lcd_cmd(0x01); // Clear display lcd_cmd(0x80); // Move to first line lcd_string("Enter Code:"); } } } }}Conclusion
A digital code lock system using the 8051 microcontroller is a secure and effective way to control access. This article outlines the components, circuit design, and programming required to build such a system. With further enhancements like multiple user codes and real-time clock integration, this system can be adapted for more complex security applications.
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