Celsius scale digital thermometer using 8051 microcontroller (AT89C51)

Celsius scale thermometer displays the ambient temperature through a LCD display. It consists of two sections. One is that which senses the temperature. This is a temperature sensor LM 35. The other section converts the temperature value into a suitable number in Celsius scale which is done by the ADC0804.

Celsius scale thermometer displays the ambient temperature through a LCD display. It consists of two sections. One is that which senses the temperature. This is a Celsius Digital Scale using 8051 temperature sensor LM 35. The other section converts the temperature value into a suitable number in Celsius scale which is done by the ADC0804. A digital thermometer can be easily made by interfacing a temperature sensor to the microcontroller AT89C51. The temperature sensor used in the project isLM35. The LM 35 IC generates a 10mV variation to its output voltage for every degree Celsius change in temperature. The Output of the temperature sensor is analog in nature so we need an analog to digital convertor for converting the analog input to its equivalent binary output.ADC 0804 is an analog to digital convertor IC used in the project. 0804 is a single channel convertor which converts the analog input up to a range of 5V to an equivalent 8-bit binary output.

A digital thermometer can be easily made by interfacing a temperature sensor to the microcontroller AT89C51. The temperature sensor used in the project is LM35. The LM 35 IC generates a 10mV variation to its output voltage for every degree Celsius change in temperature. The Output of the temperature sensor is analog in nature so we need an analog to digital convertor for converting the analog input to its equivalent binary output. The ADC 0804

is the analog to digital convertor IC used in the project. 0804 is a single channel convertor which converts the analog input up to a range of 5V to an equivalent 8-bit binary output.

The step size is defined by the voltage applied at the Vref/2 pin of the ADC IC. For example, if the voltage at Vref/2 pin is set to 1.28V then ADC has a step size of 10 mV. So if the input voltage is 1V the equivalent binary output of ADC will be 100 or 0110 0100 in binary. The 8 bit binary output of the ADC is incremented by one for every 10 mV rise of input voltage. Different step size can be selected by changing the voltage input to the Vref/2 pin. The step size of the ADC is calibrated using a preset to match the actual temperature. Once the ADC is calibrated it will give the correct output further. The binary output of ADC is fed parallel to a port of the microcontroller .The microcontroller reads the input through ADC and displays the corresponding decimal value on LCD

indicating the temperature.

Project Source Code

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//Program to make a digital thermometer with display in centigrade scale

#include<reg51.h>
#define port P3
#define adc_input P1
#define dataport P0
#define sec 100
sbit rs = port^0;
sbit rw = port^1;
sbit e = port^2;

sbit wr= port^3;
sbit rd= port^4;
sbit intr= port^5;

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 command 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;
//delay(100);
return;
}

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

void shape()     // Function to create the shape of degree
{
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;
test_final=test_intermediate3;
lcd_cmd(0xc1); 
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); 
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();
}
}


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