Digital Room Thermometer - Electronics-Lab.com (2024)

The firmware was developed on mikroC compiler. The in-built libraries for DS1820 makes the firmware development easier. The code is provided with adequate comments so that the reader won’t have much difficulty in understanding programming logic. The PIC microcontroller uses internal oscillator at 4.0 MHz. In the Edit Project window of mikroC, select internal clock, MCLR enabled, WDT Disabled, and Power On Timer Enabled.

/* Digital Room Thermometer using PIC16F688 Copyright@Rajendra Bhatt July 13, 2010*/// LCD module connectionssbit LCD_RS at RC4_bit;sbit LCD_EN at RC5_bit;sbit LCD_D4 at RC0_bit;sbit LCD_D5 at RC1_bit;sbit LCD_D6 at RC2_bit;sbit LCD_D7 at RC3_bit;sbit LCD_RS_Direction at TRISC4_bit;sbit LCD_EN_Direction at TRISC5_bit;sbit LCD_D4_Direction at TRISC0_bit;sbit LCD_D5_Direction at TRISC1_bit;sbit LCD_D6_Direction at TRISC2_bit;sbit LCD_D7_Direction at TRISC3_bit;// End LCD module connections// Back Light Switch connected to RA1sbit BackLight at RA1_bit;// Define Messageschar message0[] = "LCD Initialized";char message1[] = "Room Temperature";// String array to store temperature value to displaychar *tempC = "000.0";char *tempF = "000.0";// Variables to store temperature register valuesunsigned int temp_whole, temp_fraction, temp_value;signed int tempinF, tempinC;unsigned short C_Neg=0, F_Neg=0, TempH, TempL;void Display_Temperature() { // convert Temp to charactersif (!C_Neg) { if (tempinC/1000) // 48 is the decimal character code value for displaying 0 on LCD tempC[0] = tempinC/1000 + 48; else tempC[0] = ' '; } tempC[1] = (tempinC/100)%10 + 48; // Extract tens digit tempC[2] = (tempinC/10)%10 + 48; // Extract ones digit // convert temp_fraction to characters tempC[4] = tempinC%10 + 48; // Extract tens digit // print temperature on LCD Lcd_Out(2, 1, tempC); if (!F_Neg) { if (tempinF/1000) tempF[0] = tempinF/1000 + 48; else tempF[0] = ' '; } tempF[1] = (tempinF/100)%10 + 48; // Extract tens digit tempF[2] = (tempinF/10)%10 + 48; tempF[4] = tempinF%10 + 48; // print temperature on LCD Lcd_Out(2, 10, tempF);}// ISR for LCD Backlightvoid interrupt(void){ if (INTCON.INTF == 1) // Check if INTF flag is set { BackLight =~BackLight; // Toggle Backlight Delay_ms(300) ; INTCON.INTF = 0; // Clear interrupt flag before exiting ISR }}void main() { TRISC = 0x00 ; TRISA = 0b00001100; // RA2, RA3 Inputs, Rest O/P's ANSEL = 0b00000000; PORTA = 0b00000000; // Start with Everything Low PORTC = 0b00000000; // Start with Everything Low CMCON0 = 0b00000111; Lcd_Init(); // Initialize LCD Lcd_Cmd(_LCD_CLEAR); // CLEAR display Lcd_Cmd(_LCD_CURSOR_OFF); // Cursor off BackLight = 1; Lcd_Out(1,1,message0); Delay_ms(1000); Lcd_Out(1,1,message1); // Write message1 in 1st row // Print degree character Lcd_Chr(2,6,223); Lcd_Chr(2,15,223);// different LCD displays have different char code for degree// if you see greek alpha letter try typing 178 instead of 223 Lcd_Chr(2,7,'C'); Lcd_Chr(2,16,'F'); // Interrupt Setup OPTION_REG = 0x00; // Clear INTEDG, External Interrupt on falling edge INTCON.INTF = 0; // Clear interrupt flag prior to enable INTCON.INTE = 1; // enable INT interrupt INTCON.GIE = 1; // enable Global interrupts do { //--- perform temperature reading Ow_Reset(&PORTA, 5); // Onewire reset signal Ow_Write(&PORTA, 5, 0xCC); // Issue command SKIP_ROM Ow_Write(&PORTA, 5, 0x44); // Issue command CONVERT_T INTCON.GIE = 1; // 1-wire library disables interrpts Delay_ms(600); Ow_Reset(&PORTA, 5); Ow_Write(&PORTA, 5, 0xCC); // Issue command SKIP_ROM Ow_Write(&PORTA, 5, 0xBE); // Issue command READ_SCRATCHPAD // Read Byte 0 from Scratchpad TempL = Ow_Read(&PORTA, 5); // Then read Byte 1 from Scratchpad TempH = Ow_Read(&PORTA, 5); temp_value = (TempH << 8)+ TempL ; // check if temperature is negative if (temp_value & 0x8000) { C_Neg = 1; tempC[0] = '-'; // Negative temp values are stored in 2's complement form temp_value = ~temp_value + 1; } else C_Neg = 0; // Get temp_whole by dividing by 2 temp_whole = temp_value >> 1 ; if (temp_value & 0x0001){ // LSB is 0.5C temp_fraction = 5; } else temp_fraction = 0; tempinC = temp_whole*10+temp_fraction; if(C_Neg) { tempinF = 320-9*tempinC/5; if (tempinF < 0) { F_Neg = 1; tempF[0] = '-'; tempinF = abs(tempinF); } else F_Neg = 0; } else tempinF = 9*tempinC/5 + 320; //--- Format and display result on Lcd Display_Temperature(); } while(1);}

Snapshots of temperature measurements