Thursday, October 25, 2012

Temperature Sensor (DS18S20 + PIC16F877A)

Here's a temperature sensor (thermometer) circuit that you can easily build. It uses the popular PIC 16F877A microcontroller. The temperature sensor is DS18S20. The DS18S20 communicates through the one-wire protocol. The PIC16F877A communicates with the DS18S20 with the one-wire protocol and gets the information for the temperature and displays it on the LCD.

The temperature range of this circuit is -55'C to +125'C.

The methods of communicating with the DS18S20 and sending/receiving commands, and reading the temperature value,  are all explained in the DS18S20 datasheet (datasheets.maximintegrated.com/en/ds/DS18S20.pdf).





Here is the code for the PIC16F877A:
(You can download the source file from: https://rapidshare.com/files/1817975964/DS18S20PIC16F877A.c)
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//Programmer: Syed Tahmid Mahbub
//Compiler: mikroC PRO for PIC v4.60
//Target PIC: PIC16F877A
--------------------------------------------------------------------------------------------------------------

sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;

sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;

unsigned char TempH;
unsigned char TempL;
unsigned char TLow;
unsigned char vDisp[9];
unsigned char DP;

void main() {
     PORTB = 0;
     TRISB = 0;
     LCD_Init();
     LCD_CMD(_LCD_CURSOR_OFF);
     LCD_CMD(_LCD_CLEAR);
     PORTD = 0;
     TRISD = 0x01;
     delay_ms(200); //Wait for sensor and LCD to stabilize
     //vDisp = "+124.5 'C"
     vDisp[4] = '.';
     vDisp[7] = 39; // '
     vDisp[8] = 'C';
     LCD_Out(1,1, "Temp:");
     while (1){
         OW_Reset(&PORTD, 0); // 'Reset command to initialize One-Wire
         OW_Write(&PORTD, 0, 0xCC); // 'Skip ROM Command
         OW_Write(&PORTD, 0, 0x44); // 'Convert_T command
         delay_ms(800); // 'Provide delay for conversion
         RD7_bit = ~RD7_bit;
         OW_Reset(&PORTD, 0); // 'Reset command to initialize One-Wire
         OW_Write(&PORTD, 0, 0xCC); // 'Skip ROM Command
         OW_Write(&PORTD, 0, 0xBE); // 'Read Scratchpad Command
         TempL = OW_Read(&PORTD,0); //Read Temperature low byte
         TempH = OW_Read(&PORTD,0); //Read Temperature high byte
         DP = TempL & 0x01; // 'Check if Temperature is integer or fractional
         if (TempH){ //If reading is negative
            vDisp[0] = '-';
            TempL = ((~TempL) + 1) >> 1;
         }
         else{
             vDisp[0] = '+';
             TempL = TempL >> 1; // 'Shift one position right (divide by 2) to get integer reading and get rid of decimal point
         }
         vDisp[1] = (TempL / 100) + 48; // 'Get hundreds and convert to ASCII
         vDisp[2] = ((TempL / 10) % 10) + 48; // 'Get tens and convert to ASCII
         vDisp[3] = (TempL % 10) + 48; // 'Get units and convert to ASCII
         if (DP){ // 'If reading is fractional, ie has 0.5 at end
            vDisp[5] = '5';
         }
         else{ // 'If reading is a whole number
            vDisp[5] = '0';
         }
         Lcd_Chr(1,8, vDisp[0]);
         Lcd_Chr(1,9, vDisp[1]);
         Lcd_Chr(1,10, vDisp[2]);
         Lcd_Chr(1,11, vDisp[3]);
         Lcd_Chr(1,12, vDisp[4]);
         Lcd_Chr(1,13, vDisp[5]);
         Lcd_Chr(1,14, vDisp[6]);
         Lcd_Chr(1,15, vDisp[7]);
         Lcd_Chr(1,16, vDisp[8]);
     }
}
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Reference documents:

DS18S20 datasheet: datasheets.maximintegrated.com/en/ds/DS18S20.pdf
PIC16F877A datasheet: ww1.microchip.com/downloads/en/devicedoc/39582b.pdf
mikroC LCD library: http://www.mikroe.com/download/eng/documents/compilers/mikroc/pro/pic/help/lcd_library.htm
mikroC One-Wire library: http://www.mikroe.com/download/eng/documents/compilers/mikroc/pro/pic/help/onewire_library.htm

8 comments:

  1. This comment has been removed by the author.

    ReplyDelete
  2. I have used DS18B20. But the program does not work properly. It shows different temperature. Please give me some suggestion.

    ReplyDelete
  3. The DS18B20 is slightly different from the DS18S20, which is what is used in my circuit.

    For a comparison of the 2 devices, check this out:

    http://www.maximintegrated.com/app-notes/index.mvp/id/4377

    For a circuit/code utilizing DS18B20, check out:

    http://www.edaboard.com/thread279990.html#post1199130

    Regards,
    Tahmid.

    ReplyDelete
  4. hello tahmid , i am using led instead of lcd ,can i use this coding ? if not ,can you give some suggestion regarding the code , ireally need your help , this is for my final year project ,my email : zu_aida87@yahoo.com

    ReplyDelete
    Replies
    1. You need to change the code that handles the display. The LCD code is written for the HD44780 controller. You need to change that to be able to display to an LED display.

      Delete
  5. tahmid brother, i've made a project using 18b20 from ur codes given here.but the problem is that i have added a relay for certain range of temperature.i have used register A for that.the relay is fluctuating. it should be turn on and remain steady.here is my code:
    // LCD module connections
    sbit LCD_RS at RB4_bit;
    sbit LCD_EN at RB5_bit;
    sbit LCD_D4 at RB0_bit;
    sbit LCD_D5 at RB1_bit;
    sbit LCD_D6 at RB2_bit;
    sbit LCD_D7 at RB3_bit;

    sbit LCD_RS_Direction at TRISB4_bit;
    sbit LCD_EN_Direction at TRISB5_bit;
    sbit LCD_D4_Direction at TRISB0_bit;
    sbit LCD_D5_Direction at TRISB1_bit;
    sbit LCD_D6_Direction at TRISB2_bit;
    sbit LCD_D7_Direction at TRISB3_bit;
    // End LCD module connections

    // Set TEMP_RESOLUTION to the corresponding resolution of used DS18x20 sensor:
    // 18S20: 9 (default setting; can be 9,10,11,or 12)
    // 18B20: 12
    const unsigned short TEMP_RESOLUTION = 12;

    char *text = "000.00";
    unsigned temp;

    void Display_Temperature(unsigned int temp2write) {
    const unsigned short RES_SHIFT = TEMP_RESOLUTION - 8;
    unsigned char temp_whole;
    unsigned int temp_fraction;
    PORTA=0;
    TRISA=0;

    // Check if temperature is negative
    if (temp2write & 0x8000) {
    LCD_Chr(2,4,'-');
    temp2write = ~temp2write + 1;
    }
    else{
    LCD_Chr(2,4,' ');
    }

    // Extract temp_whole
    temp_whole = temp2write >> RES_SHIFT ;
    //led blinking
    if(temp_whole>=20 && temp_whole<40)

    {
    porta.f0=1;
    }
    if(temp_whole>=40 && temp_whole<60)
    {
    portd.f1=1;
    }
    if(temp_whole>=60)
    {
    portd.f2=1;
    }

    // Convert temp_whole to characters
    if (temp_whole/100)
    text[0] = temp_whole/100 + 48;
    else
    text[0] = '0';

    text[1] = (temp_whole/10)%10 + 48; // Extract tens digit
    text[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
    text[4] = temp_fraction/1000 + 48; // Extract thousands digit
    text[5] = (temp_fraction/100)%10 + 48; // Extract hundreds digit


    // Print temperature on LCD
    Lcd_Out(2, 5, text);

    }

    void main() {
    ADCON1=0x06;

    Lcd_Init(); // Initialize LCD
    Lcd_Cmd(_LCD_CLEAR); // Clear LCD
    Lcd_Cmd(_LCD_CURSOR_OFF); // Turn cursor off
    Lcd_Out(1, 1, " Temperature: ");
    // Print degree character, 'C' for Centigrades
    Lcd_Chr(2,11,223); // Different LCD displays have different char code for degree
    // If you see greek alpha letter try typing 178 instead of 223

    Lcd_Chr(2,12,'C');

    //--- Main loop
    do {
    //--- Perform temperature reading
    Ow_Reset(&PORTE, 2); // Onewire reset signal
    Ow_Write(&PORTE, 2, 0xCC); // Issue command SKIP_ROM
    Ow_Write(&PORTE, 2, 0x44); // Issue command CONVERT_T
    Delay_us(120);

    Ow_Reset(&PORTE, 2);
    Ow_Write(&PORTE, 2, 0xCC); // Issue command SKIP_ROM
    Ow_Write(&PORTE, 2, 0xBE); // Issue command READ_SCRATCHPAD

    temp = Ow_Read(&PORTE, 2);
    temp = (Ow_Read(&PORTE, 2) << 8) + temp;

    //--- Format and display result on Lcd
    Display_Temperature(temp);

    Delay_ms(500);
    } while (1);
    }

    ReplyDelete
  6. Dear Tahmid,,

    it 's good project..,,,can you post the code using hitech compiler

    ReplyDelete
  7. Hello all !!! Masud Al Hasan -> your problem in code (led blinking) is caused by TRISA & PORTA . This command must to be out of ,, void Display_Temperature(unsigned int temp2write) " , at the begining of code. Good luck ;)

    ReplyDelete