#include <reg51.h> // Includes 8051 microcontroller definitions

// Function declarations
void delay(unsigned int time); // Generates a delay (approximately 1ms per iteration)
void lcd_cmd(unsigned char a); // Sends a command to the LCD
void lcd_data(unsigned char b); // Sends data (characters) to the LCD
void lcd_init(void); // Initializes the LCD
void lcd_str(unsigned char *str); // Displays a string on the LCD
void display_temperature(unsigned char temp); // Displays the temperature on the LCD
void start_dht11(void); // Initializes communication with the DHT11 sensor
unsigned char read_dht11_data(void); // Reads data from the DHT11 sensor

// Pin definitions
sbit rs = P2^0; // Register select pin for LCD
sbit en = P2^1; // Enable pin for LCD
sbit buz = P2^5; // Buzzer control pin
sbit dht11_pin = P2^2; // Data pin for DHT11 sensor (connected to P2^2)
sfr ldata = 0xB0; // Data port for LCD (Port 3)

// Variables
unsigned char temperature; // Variable to hold temperature value

// Main function
void main ()
{
    lcd_init(); // Initialize LCD
    buz = 0; // Ensure the buzzer is off at the start

    // Display welcome message
    lcd_str("    WELCOME    ");
    lcd_cmd(0xc0);
    lcd_str("   TO PROJECT   ");
    delay(200);
    lcd_cmd(0x01);

    lcd_cmd(0x81); // Display project title
    lcd_str("  TEMPERATURE  ");
    lcd_cmd(0xc2);
    lcd_str("   ALERT   ");
    delay(200);
    lcd_cmd(0x01);

    lcd_cmd(0x80); // Display temperature label
    lcd_str("  Temp =");
    lcd_cmd(0x8b);
    lcd_data((char)223); // Display degree symbol
    lcd_str("C");

    while (1)
    {
        // Read temperature from DHT11
        start_dht11();
        temperature = read_dht11_data();

        // Display temperature
        lcd_cmd(0x89);
        display_temperature(temperature);

        // Check if temperature exceeds threshold of 35°C
        if (temperature > 35)
        {
            lcd_cmd(0xC0);
            lcd_str("HIGH TEMP ALERT!");
            buz = 1; // Turn buzzer on
        }
        else
        {
            lcd_cmd(0xC0);
            lcd_str("                ");
            buz = 0; // Turn buzzer off
        }

        delay(1000); // 1-second delay before the next reading
    }
}

// Function to display temperature on LCD
void display_temperature(unsigned char temp)
{
    unsigned char d1, d2;
    d1 = temp / 10; // Tens digit
    d2 = temp % 10; // Ones digit
    lcd_data(d1 + 0x30); // Convert to ASCII and display tens digit
    lcd_data(d2 + 0x30); // Convert to ASCII and display ones digit
}

// Function to initialize DHT11 communication
void start_dht11(void)
{
    dht11_pin = 0; // Pull data pin low
    delay(18); // Wait for at least 18ms
    dht11_pin = 1; // Pull data pin high
    delay(20); // Wait for DHT11 to respond
}

// Function to read 40 bits from DHT11 and extract temperature
unsigned char read_dht11_data(void)
{
    unsigned char i, j, result = 0, dht11_data[5] = {0, 0, 0, 0, 0};

    for (i = 0; i < 5; i++)
    {
        for (j = 0; j < 8; j++)
        {
            while (!dht11_pin); // Wait for DHT11 to pull data pin low
            delay(30); // Wait for 30us

            // If data pin is high, set the appropriate bit in the result
            if (dht11_pin == 1)
                dht11_data[i] |= (1 << (7 - j));

            while (dht11_pin); // Wait for data pin to go low again
        }
    }

    // The temperature integral value is stored in dht11_data[2]
    return dht11_data[2]; // Return temperature byte
}

// LCD initialization function
void lcd_init()
{
    lcd_cmd(0x38); // Initialize LCD for 8-bit mode
    lcd_cmd(0x0C); // Display on, cursor off
    lcd_cmd(0x01); // Clear display
    lcd_cmd(0x80); // Set cursor to beginning of first line
}

// Updated delay function for 89S52 microcontroller
void delay(unsigned int time)
{
    unsigned int i, j;
    for (i = 0; i < time; i++)
    {
        for (j = 0; j < 1275; j++) // Approx 1ms delay for 89S52
        {
            // Do nothing, just waste time
        }
    }
}

// Function to send command to LCD
void lcd_cmd(unsigned char a)
{
    rs = 0; // Set for command mode
    ldata = a; // Load command to data port
    en = 1; // Enable LCD
    delay(2); // Short delay
    en = 0; // Disable LCD
    delay(2); // Short delay
}

// Function to send data (characters) to LCD
void lcd_data(unsigned char b)
{
    rs = 1; // Set for data mode
    ldata = b; // Load data to data port
    en = 1; // Enable LCD
    delay(2); // Short delay
    en = 0; // Disable LCD
    delay(2); // Short delay
}

// Function to display string on LCD
void lcd_str(unsigned char *str)
{
    while (*str) // Loop until the end of the string
    {
        lcd_data(*str++); // Send each character to the LCD
    }
}

This my code for high temperature alert system for my course project.And i also created proteus schematics.It doesn't working.The temperature value is blank.And also the reset button is not working properly.I atttach the hex file ,c code file below

 

Forget the complex code.

Write the shortest program to show the letter "A" on the display.
In fact you can even take a few steps before that. Write a simple program to make a single LED flash.
Then test that you can generate pulses on all control and data bits.

After you have done all those tests, there is one other hardware check to be made.
What do you see when the power to the LCD is applied without any code running?
Adjust the contrast setting so that you can see a row of dark rectangles.