Experiment No. 11: Temperature Data Logger Using PIC16F628A Microcontroller

This project is the combination of the two experiments that we already did in past: Experiment No. 4 and 10. In experiment 4, we demonstrated how to use the mikroC 1-wire library to read temperature data from a digital sensor DS1820, and display the value on a LCD screen. Now we are going to use the hardware UART to transfer the temperature data from the PIC to a PC (Exp. No. 10). The Hyper-Terminal program running on a PC will receive the temperature values and display on screen. The temperature data from the microcontroller will be sent in every 15 sec.

Experimental Setup:

The setup for this experiment is same as the Experiment no. 10 with a DS1820 inserted in its 3-pin female header receiver on the board. The data output of DS1820 is connected to RB.0 (see articles  Exp. No. 4 and 1-Wire Protocol for detail). You need to rebuild the same TTL to RS232 level shifter circuit on a breadboard and set up a hyper-terminal to receive data at 9600 baud rate.

Software:

 /*
 * Project name:
     Temperature Data Logger

    PIC16F628A reads digital temperature data from a DS1820 chip, and

    send it to a PC through RS232 port to display on hyperterminal window.
 * Copyright:
     (c) Rajendra Bhatt, 2009.
*/

// String array to store temperature value to display
char *temp = "000.00";

// Temperature Resolution : No. of bits in temp value = 9
const unsigned short TEMP_RES = 9;

// Variable to store temperature register value
unsigned temp_value;

void Display_Temperature(unsigned int temp2write) {
  const unsigned short RES_SHIFT = TEMP_RES - 8;

  // Variable to store Integer value of temperature
  char temp_whole;

  // Variable to store Fraction value of temperature
  unsigned int temp_fraction;

  // check if temperature is negative
  if (temp2write & 0x8000) {
     temp[0] = '-';
     // Negative temp values are stored in 2's complement form
     temp2write = ~temp2write + 1;
     }

  // Get temp_whole by dividing by 2 (DS1820 9-bit resolution with
  // 0.5 Centigrade step )
  temp_whole = temp2write >> RES_SHIFT ;

  // convert temp_whole to characters
  if (temp_whole/100)
  // 48 is the decimal character code value for displaying 0 on LCD
     temp[0] = temp_whole/100  + 48;
  else
     temp[0] = '0';

  temp[1] = (temp_whole/10)%10 + 48;             // Extract tens digit
  temp[2] =  temp_whole%10     + 48;             // Extract ones digit

  // extract temp_fraction and convert it to unsigned int
  temp_fraction  = temp2write << (4-RES_SHIFT);
  temp_fraction &= 0x000F;
  temp_fraction *= 625;

  // convert temp_fraction to characters
  temp[4] =  temp_fraction/1000    + 48;         // Extract tens digit
  temp[5] = (temp_fraction/100)%10 + 48;         // Extract ones digit

  // Send temperature to RS232
  UART1_Write(10); // Line Feed
  UART1_Write(13); // Carriage Return
  UART1_Write_Text("Temperature= ");
  UART1_Write_Text(temp);

 }

//unsigned char _data = 0x1E;
void main() {
CMCON = 7;       // Disable Comparators
UART1_Init(9600);
Delay_ms(100);
 //--- main loop
  do {
    //--- perform temperature reading
    Ow_Reset(&PORTB, 0);      // Onewire reset signal
    Ow_Write(&PORTB, 0, 0xCC);   // Issue command SKIP_ROM
    Ow_Write(&PORTB, 0, 0x44);   // Issue command CONVERT_T
    Delay_ms(600);
    // If this delay is less than 500ms, you will see the first reading on LCD
    //85C which is (if you remember from my article on DS1820)
    //a power-on-reset value.

    Ow_Reset(&PORTB, 0);
    Ow_Write(&PORTB, 0, 0xCC);    // Issue command SKIP_ROM
    Ow_Write(&PORTB, 0, 0xBE);    // Issue command READ_SCRATCHPAD

    // Read Byte 0 from Scratchpad
    temp_value =  Ow_Read(&PORTB, 0);
    // Then read Byte 1 from Scratchpad and shift 8 bit left and add the Byte 0
    temp_value = (Ow_Read(&PORTB, 0) << 8) + temp_value;

    //--- Format and display result on Lcd
    Display_Temperature(temp_value);
    Delay_ms(30000);

    } while (1);
}

Output: