LM35 Project Software

3 min

The firmware required to interface with the sensor performs several tasks.

Configures the microcontroller to read the analog value
Converts the analog value to a digital number
Formats that value for export

Microcontroller

The device chosen is the PIC16F887, and while it is far more in terms of resources it will provide a good base to build on and with for later projects or adding on additional features.

What is needed from the microcontroller is:

One of the Analog Inputs
PORTB for the LCD Display
Comport to share the data with the outside world

Full Code Sample

The full code sample is shown below and can be copied from the code block.

The code sample is also available from GitHub.

unsigned char ch;
unsigned int adc_rd;
char *text;
long tlong;
char *tempc = "000.0";

void deviceSetup(){
  INTCON = 0;                              // disable all interrupts
  
  ANSEL  = 0x04;                           // Configure AN2 pin as analog input
  TRISA  = 0x04;
  ANSELH = 0;  
  ADCON1 = 0x82;                       // configure VDD as Vref, and analog channels
  TRISA  = 0xFF;                       // designate PORTA as input  

  UART1_Init(9600);
  Delay_ms(100);
}

void main() {
                            
  Lcd_Config(&PORTB, 4, 5, 6, 3, 2, 1, 0); // Lcd_Init_EP5, see Autocomplete
  LCD_Cmd(LCD_CURSOR_OFF);                 // send command to LCD (cursor off)
  LCD_Cmd(LCD_CLEAR);                      // send command  to LCD (clear LCD)

  text = "LM 35 Project";               // assign text to string
  LCD_Out(1,1,text);                       // print string a on LCD, 1st row, 1st column
    
  Delay_ms(2000);
  text  = "Temp:";                      // assign text to string


  while (1) {
    adc_rd  = ADC_read(2);                 // get ADC value from 2nd channel
    LCD_Out(2,1,text);                     // print string a on LCD, 2nd row, 1st column

    tlong = (long)adc_rd * 5000;           // covert adc reading to milivolts
    tlong = tlong / 1023;                  // 0..1023 -> 0-5000mV
    
    ch = tlong / 1000;                 // extract leading temp digit
    tempc[1] = ch+48;
    
    ch = (tlong / 100) % 10;            // extract 0.1 temp digit
    LCD_Chr_CP(48+ch);                     // write ASCII digit at cursor point
    tempc[2] = ch+48;

    ch = (tlong / 10) % 10;             // extract 0.01 temp digit
    tempc[3] = ch+48;
    LCD_Chr_CP(48+ch);                     // write ASCII digit at cursor point
    LCD_Chr_CP(48+ch);                     // write ASCII digit at cursor point
    LCD_Chr_CP('C');
    tempc[4] = ch+48;
    
    UART1_Write(tempc[2]);
    UART1_Write(tempc[3]);
    UART1_Write_Text(".");
    UART1_Write(tempc[4]);
    
    UART1_Write(13);
    UART1_Write(10);
    Delay_ms(100);    
    
  }
}//~!