Measure temperature using DS1820 sensor. Use ‘1-wire’ protocol...

Temperature measurement is one of the most common operations performed by the microcontroller. A DS1820 temperature sensor is used here for measuring. It is capable of measuring temperature within the range of -55 °C to 125 °C with a 0.5 °C accuracy. To transfer data to the microcontroller, a special type of serial communication called 1-wire is used. Due to their simple and wide application, such sensors are run and controlled by functions stored in the One_Wire library. This library contains three functions in total:

• Ow_Reset is used to reset sensor;
• Ow_Read is used for receiving data from sensor; and
• Ow_Write is used for sending commands to sensor.

Here you can see the advantage of using libraries with ready-to-use functions. You obviously don’t need to study documentation provided by the manufacturer so as to use this sensor properly. It is sufficient to copy appropriate functions to the program. If you want to know how any of these functions is declared, just right click on it and select the Help option.

' Header******************************************************
program example_12 ' Program name

dim LCD_RS as sbit at RB4_bit ' Lcd module connections
LCD_EN as sbit at RB5_bit
LCD_D4 as sbit at RB0_bit
LCD_D5 as sbit at RB1_bit
LCD_D6 as sbit at RB2_bit
LCD_D7 as sbit at RB3_bit
LCD_RS_Direction as sbit at TRISB4_bit
LCD_EN_Direction as sbit at TRISB5_bit
LCD_D4_Direction as sbit at TRISB0_bit
LCD_D5_Direction as sbit at TRISB1_bit
LCD_D6_Direction as sbit at TRISB2_bit
LCD_D7_Direction as sbit at TRISB3_bit ' End Lcd module connections

' Set TEMP_RESOLUTION to the corresponding resolution of the DS18x20 sensor in use:
' 18S20: 9 (default setting can be 9,10,11 or 12); 18B20: 12

const TEMP_RESOLUTION as byte = 9 ' Constant TEMP_RESOLUTION is of byte type
dim text as char[9] ' Variable text is of char type
temp as word ' Variable temp is of word type

sub procedure Display_Temperature( dim temp2write as word )
 const RES_SHIFT = TEMP_RESOLUTION - 8
 dim temp_whole as byte ' Variable temp_whole is of byte type
 temp_fraction as word ' Variable temp_fraction is of word type
 text = "000.0000"

 if (temp2write and 0x8000) then ' Check if temperature is negative
 text[0] = "-"
 temp2write = not temp2write + 1
 end if

 temp_whole = word(temp2write >> RES_SHIFT) ' Extract temp_whole
 
 if ( temp_whole div 100 ) then ' Convert temp_whole to characters
 text[0] = temp_whole div 100 + 48
 else
 text[0] = "0"
 end if

 text[1] = (temp_whole div 10) mod 10 + 48 ' Extract tens
 text[2] = temp_whole mod 10 + 48 ' Extract ones
 temp_fraction = word(temp2write << (4-RES_SHIFT)) ' Extract temp_fraction
 temp_fraction = temp_fraction and 0x000F ' and convert it to
 temp_fraction = temp_fraction * 625 ' unsigned int
 text[4] = word(temp_fraction div 1000) + 48 ' Extract thousands
 text[5] = word((temp_fraction div 100) mod 10 + 48) ' Extract hundreds
 text[6] = word((temp_fraction div 10) mod 10 + 48) ' Extract tens
 text[7] = word(temp_fraction mod 10) + 48 ' Extract ones
 Lcd_Out(2, 5, text) ' Print temperature on Lcd
end sub

main: ' Start of program
ANSEL = 0 ' Configure analog pins as digital I/O
ANSELH = 0

text = "000.0000"
Lcd_Init() ' Initialize Lcd
Lcd_Cmd(_LCD_CLEAR) ' Clear Lcd
Lcd_Cmd(_LCD_CURSOR_OFF) ' Turn off cursor
Lcd_Out(1, 1, " Temperature: ")

Lcd_Chr(2,13,178) ' Print degree character, "C" for Centigrades
' Different LCD displays have different char code for degree
Lcd_Chr(2,14,"C") ' If you see greek letter ‘alpha’ type 178 instead of 223

while 1 ' Temperature is read in the main loop
 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

 Display_Temperature(temp) ' Format and display result on Lcd

 Delay_ms(520) ' 520 mS delay
wend
end. ' End of program

In order to make this example work properly, it is necessary to check the following libraries in the Library Manager prior to compiling:

• One_Wire
• LCD