Temperature measurement using DS1820 sensor. Use of ‘1-wire’ protocol...
Temperature measurement is one of the most common tasks performed by the microcontroller. A DS1820 sensor is used for measurement here. It is capable of measuring temperature in the range of -55 °C to 125 °C with 0.5 °C accuracy. For the purpose of transferring data to the microcontroller, a special type of serial communication called 1-wire is used. Due to a simple and wide use of these sensors, commands used to run and control them are in the form of functions stored in the One_Wire library. There are three functions in total:/*Header******************************************************/ // 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 const unsigned short TEMP_RESOLUTION = 9; char *text = "000.0000"; unsigned temp; void Display_Temperature(unsigned int temp2write) { const unsigned short RES_SHIFT = TEMP_RESOLUTION - 8; char temp_whole; unsigned int temp_fraction; // check if temperature is negative if (temp2write & 0x8000) { text[0] = '-'; temp2write = ~temp2write + 1; } // extract temp_whole temp_whole = temp2write >> RES_SHIFT ; // 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 text[6] = (temp_fraction/10)%10 + 48; // Extract tens digit text[7] = temp_fraction%10 + 48; // Extract ones digit // Display temperature on LCD Lcd_Out(2, 5, text); } void main() { ANSEL = 0; // Configure AN pins as digital I/O ANSELH = 0; C1ON_bit = 0; // Disable comparators C2ON_bit = 0; Lcd_Init(); // Initialize LCD Lcd_Cmd(_LCD_CLEAR); // Clear LCD Lcd_Cmd(_LCD_CURSOR_OFF); // Turn the cursor off Lcd_Out(1, 1, " Temperature: "); // Print degree character, 'C' for Centigrades Lcd_Chr(2,13,223); // different LCD displays have different char code for degree // if you see greek alpha letter try typing 178 instead of 223 Lcd_Chr(2,14,'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); }In order to make this example work properly, it is necessary to tick off the following libraries in the Library Manager prior to compiling: