[51] temperature monitoring system using LM35 and 8051

[phrbob93]

i was doing a project of temperature monitoring system using 8051 and LM35 for that i use ADC0804 programming
my whole setup is going great previously..
i was getting the correct temperature on LCD..but don't know what happened recently.. on room temperature which should be 25 degree Celsius it is showing 57 degree..
i rotate the dial of POT on ADC0804 to least and the least temperature i am getting is 57 degree

how i can overcome this problem
my hardware circuit and code is as follows

//Program to display temperature in Celsius and Farenheit scale.

#include<reg51.h>
#define port P3
#define adc_input P1
#define dataport P2
#define sec 100
sbit rs = port^7;
sbit rw = port^6;
sbit e = port^5;
sbit led = port^0;
sbit wr= port^3;
sbit rd= port^2;
sbit intr= port^4;

int test_intermediate3=0, test_final=0,test_intermediate1[10],test_intermediate2[3]={0,0,0};

void delay(unsigned int msec )
{
    int i ,j ;
    for(i=0;i<msec;i++)
        for(j=0; j<1275; j++);
}

void lcd_cmd(unsigned char item)    // Function to send commands to LCD
{
    dataport = item;
    rs= 0;
    rw=0;
    e=1;
    delay(1);
    e=0;
    return;
}

void lcd_data(unsigned char item)    // Function to send data to LCD
{
    dataport = item;
    rs= 1;
    rw=0;
    e=1;
    delay(1);
    e=0;
    return;
}

void lcd_data_string(unsigned char *str)  // Function to string to LCD
{
    int i=0;
    while(str[i]!='\0')
    {
        lcd_data(str[i]);
        i++;
        delay(10);
    }
    return;
}

void shape()        // Function to make the shape of degree symbol
{
    lcd_cmd(64);
    lcd_data(2);
    lcd_data(5);
    lcd_data(2);
    lcd_data(0);
    lcd_data(0);
    lcd_data(0);
    lcd_data(0);
    lcd_data(0);
}
       
void convert()     // Function to convert the values of ADC into numeric value to be sent to LCD
{
    int    s;
    lcd_cmd(0x81);      
    delay(2);
    lcd_data_string("TEMP:");
    test_final=(((9*test_intermediate3)/5)+32);
    s=test_final/100;
    test_final=test_final%100;
    lcd_cmd(0x88);
    if(s!=0)
    lcd_data(s+48);
    else
    lcd_cmd(0x06);
    s=test_final/10;
    test_final=test_final%10;
    lcd_data(s+48);
    lcd_data(test_final+48);
    lcd_data(0);
    lcd_data('F');
    lcd_data(' ');

    test_final=test_intermediate3;
				if(test_final>35)
		    led=1;
		
	   	else
			led=0;
    lcd_cmd(0xc1);        //Setting  cursor to first position of first line
    delay(2);
    lcd_data_string("TEMP:");
    s=test_final/100;

    test_final=test_final%100;
    lcd_cmd(0xc8);
    if(s!=0)
    lcd_data(s+48);
    else
    lcd_cmd(0x06);
    s=test_final/10;
    test_final=test_final%10;
    lcd_data(s+48);
    lcd_data(test_final+48);
    lcd_data(0);
    lcd_data('c');
    lcd_data(' ');
    delay(2);
}

void main()
{
    int i,j;
    adc_input=0xff;
    lcd_cmd(0x38);        //2 Line, 5X7 Matrix display
    lcd_cmd(0x0c);        //Display On, Cursor blinking
    delay(2);
    lcd_cmd(0x01);        // clear screen
    delay(2);

    while(1)
    {
        for(j=0;j<3;j++)
        {
            for(i=0;i<10;i++)
            {
                delay(1);
                rd=1;
                wr=0;
                delay(1);
                wr=1;
                while(intr==1);
                rd=0;
                lcd_cmd(0x88);
                test_intermediate1[i]=adc_input/10;
                delay(1);
                intr=1;
            }
					
            for(i=0;i<10;i++)
            test_intermediate2[j]=test_intermediate1[i]+test_intermediate2[j];
        }

        test_intermediate2[0]=test_intermediate2[0]/3;
        test_intermediate2[1]=test_intermediate2[1]/3;
        test_intermediate2[2]=test_intermediate2[2]/3;
        test_intermediate3=test_intermediate2[0]+test_intermediate2[1]+test_intermediate2[2];
        shape();
        convert();
    }
}

the circuit diagram is in the attachment

 

[S.P.S]

Check th voltage on Vref/2 pin ,you should make it 1.28V to get exact temperature. Or you can apply correction on software side according to your reference.