System Overview This system combines an 8051 microcontroller, infrared control, temperature sensing, and serial communication to implement a secure password-protected lock mechanism. The system architecture includes:

Password verification via keypad Infrared remote control interface Temperature monitoring using DS18B20 sensor Visual feedback through LCD and 7-segment display Alarm activation via buzzer Motor control for lock actuation

Hardware Configuration

Microcontroller Connections

Keypad - Port 0 7-segment display - Port 2 LCD interface - P2.5 (RW), P2.6 (RS), P2.7 (EP) Buzzer - P1.0 Stepper motor control - P1.2 to P1.7 Infrared sensor - P3.2 Temperature sensor (DS18B20) - P3.7

Key Software Components

Temperature Sensor Interface

void ds18b20_init() {
    DQ = 1; _nop_();
    DQ = 0; delay_us(480);
    DQ = 1; delay_us(80);
    // Verify presence pulse
}

unsigned char ds_read_byte() {
    unsigned char i, value = 0;
    for (i = 0; i < 8; i++) {
        DQ = 0; value >>= 1; DQ = 1;
        if (DQ) value |= 0x80;
        delay_us(2);
    }
    return value;
}

int get_temperature() {
    unsigned char low, high;
    ds18b20_init();
    ds_write_byte(0xCC); // Skip ROM
    ds_write_byte(0x44); // Start conversion
    delay_ms(750);
    
    ds18b20_init();
    ds_write_byte(0xCC);
    ds_write_byte(0xBE); // Read scratchpad
    
    low = ds_read_byte();
    high = ds_read_byte();
    
    return ((high * 256 + low) * 62.5);
}

LCD Display Management

bit lcd_busy_check() {
    LCD_RS = 0; LCD_RW = 1; LCD_EP = 1;
    bit result = (P0 & 0x80);
    LCD_EP = 0;
    return result;
}

void lcd_command(unsigned char cmd) {
    while (lcd_busy_check());
    LCD_RS = 0; LCD_RW = 0;
    P0 = cmd; LCD_EP = 1; _nop_(); LCD_EP = 0;
}

void lcd_write_char(unsigned char data) {
    while (lcd_busy_check());
    LCD_RS = 1; LCD_RW = 0;
    P0 = data; LCD_EP = 1; _nop_(); LCD_EP = 0;
}

Serial Communication

void serial_init() {
    SCON = 0x50; // 8-bit, variable baud
    PCON |= 0x80; // Double baud rate
    TMOD |= 0x20; // Timer 1, mode 2
    TH1 = 0xF3; TL1 = 0xF3; // 4800 baud at 12MHz
    TR1 = 1; 
    ES = 1; EA = 1; // Enable serial and global interrupts
}

void send_byte(char data) {
    SBUF = data;
    while (!TI);
    TI = 0;
}

Infrared Remote Handling

void ir_interrupt() interrupt 0 {
    // Signal decoding logic
    if (validate_ir_signal()) {
        decode_ir_data();
        process_ir_command();
    }
}

System Operation The system operates in multiple modes selected through serial communication:

Password Lock Mode Hendles keypad input verification and motor control for lock mechanism

Temperature Monitoring Dsiplays real-time temperature on LCD with DS18B20 sensor

Infrared Control Processes remote control commands for system configuration

The system provides audio feedback through the buzzer for successful operations or invalid attempts.