Temperature Meter using Microcontroller and LM35 Temperature Sensor

We can  build a Temperature meter by pic18f2550 microcontroller and we need a temperature sensor . In this project we will use LM35 temperature sensor and it is a popular temperature sensor .Look at the picture which is given below .

The Picture has been taken from internet

LM35 produce different voltage outputs at different temperatures . LM35 increase it's output voltage 10mV or 0.01v  for each degree increment of temperature . That means 0.01 v per degree centigrade. 

Now we need to get a microcontroller as a system to read temperature from sensor . We will use ADC of the microcontroller and the reading will be shown in LCD display . It's the basic idea of the project .

We need a basic knowledge about ADC . Let's  take a look at here :

ADCON1 Register

Basically ADC is like as voltage divider . According to voltage It produce output .
bit 5 : VCFG0: Voltage Reference Configuration bit (VREF- source)
1 = VREF- (AN2)
0 = VSS or 0 volt

bit 4 :VCFG0: Voltage Reference Configuration bit (VREF+ source)
1 = VREF+ (AN3)
0 = VDD or 5volt

We will set  VCFG0[bit 5]=0and VCFG0[bit4]=0 . So we will get highest value 5volt[1023] and lowest value 0volt[0].The ADCON1 is a 10 bit register that means  (2 to the power 10) is it's highest counting capacity and the result is 1024 . So this register can count from 0 to 1023 . When 0 volt , we get reading at RA0 pin  0 .When 5 volt , we get reading at RA0 pin 1023. It means 5volt equivalent to 1023 .

 If  1023 reading value    equal   to 5 volt.
So 1      reading value    equal   to  5/1023 volt
So 'read_val'  reading  value   equal  to (5/1023)*read_val .volt .
As we know LM35 reading can be changed  with  0.01 v per degree centigrade change . According to the datasheet 10mV = 1 degree centigrade temperature .The temperature calculation should be like that :
    0.01 volt   for     1      degree centigrade Temperature
so  1     ,,       ,,  (1/0.01)   ,,         ,,              ,,

and (5/1023)*read_val    volt    for  [{(5/1023)*read_val }/0.01]  degree centigrade Temperature .

Source Code :

sbit LCD_RS at LATB7_bit;
sbit LCD_EN at LATB6_bit;
sbit LCD_D4 at LATB5_bit;
sbit LCD_D5 at LATB4_bit;
sbit LCD_D6 at LATB3_bit;
sbit LCD_D7 at LATB2_bit;

sbit LCD_RS_Direction at TRISB7_bit;
sbit LCD_EN_Direction at TRISB6_bit;
sbit LCD_D4_Direction at TRISB5_bit;
sbit LCD_D5_Direction at TRISB4_bit;
sbit LCD_D6_Direction at TRISB3_bit;
sbit LCD_D7_Direction at TRISB2_bit;
// End LCD module connections

double source=0;
int temperature=0;
char txt[15];

void main() {
ADCON1=0x0E;                  // Configure RA0 pin as input
CMCON=7;
TRISB.F0=0;
  ADC_Init();                        // Initialize ADC

  Lcd_Init();                        // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);               // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

  Lcd_Out(1, 3, "Temperature");
                  // Different LCD displays have different
  Lcd_Chr(2,12,223);                   //   char code for degree
  Lcd_Chr(2,13,'C');                  // Display "C" for Celsius
  while(1){
 source=Adc_Read(0);
 source=(source*5)/1023;
 source=source/0.01;
if(source>30){       // when temperature goes higher than 30 degree , fan turns on .
PORTB.F0=1;
} 
else{                    // when temperature goes lower than 30 degree , fan remains off .
 PORTB.F0=0;
}
inttostr(source,txt);
Lcd_Out(2,1,txt);



}
}

Circuit :

During temperature lower than 30 degree:

During temperature higher than 30 degree:

This Project's Proteus Simulation in Youtube , Please Watch This:

                             

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Thank You !!