09.c

Thermostat Project using DS18B20 and P89V51RD2 Microcontroller. Compiler used is SDCC. Schematic Inc

//Program Description: Emulate a Thermostat on UNI-51-SDK using DS18B20 and Relays
//Author: Anurag Chugh ([e-mail])

#include"LCD.H"
		//This Library is rquired for displaying the Temperature and Relay Status on the LCD

#include"CALCULATOR.H"
		//This Library to handle floating point operations. DS18B20 is very accurate and so we need a floating
		//variable to store the temperature. See page 4 of DS18B20 Datasheet to see the Temperature Register Format.
		//Specially note the number of binary digits of precision (ie 2^6 to 2^-4)

#include"DS1820.H"
		//This contains the function to access the DS18B20 over the 1-wire bus.


//The following are the predefined temperatures above which each of the relays would turn on
#define RELAY1_TEMP 36.0000		//Degrees Centigrade
#define RELAY2_TEMP 38.0000		//Degrees Centigrade


//Pins (Register Bits) of the microcontroller to which Relay Drivers and hence the Relay Coils are connected.
#define RELAY1_STATE P2_6
#define RELAY2_STATE P2_7

//This is to make the program more readable.
//Writing a 1 to the pin would turn ON the corresponding relay.
//Writing a 0 to the pin would turn OFF the corresponding relay.
#define ON 1
#define OFF 0

unsigned char MyTemp[9];

//This function reads the temperature from the DS18B20 and returns the temperature in a float variable
//It also converts this float to a String and saves it at the location in the memory to which the passed char pointer points to.
float get_temperature(char *tempstring)
{
	unsigned char sign, tempinteger,tempdecimal;
	float temperature;
	ReadTemp(&MyTemp[0]);
	
	//Conversion to Floating Point -->
	//Converting the raw temperature data to floating point variable.
	//Refer Page 4 of DS18B20 for the Temperature Registers (TH & TL) bit place values.
	sign = ((MyTemp[1]&0xF0) == 0xF0)? '-' : '+';				
	tempinteger  = (MyTemp[0] >> 4) + ( (MyTemp[1]&0x07) << 4 );		
	tempdecimal = (MyTemp[0]&0x0F);

	temperature = (float)tempinteger + ( ((float)tempdecimal) * 0.0625);

	if(sign == '-')
		temperature = -1*temperature;
	//<--Conversion to Floating Point
	
	
	ftoa(temperature,4,tempstring);		//Convert float to char array for display on LCD
	return temperature;
}

void main(void)
{
	
	float temperature;
	char tempstring[10];
	int i;
	
	RELAY1_STATE = OFF;	//At startup, both relays are off.
	RELAY2_STATE = OFF;
	
	LCD_init();		//Initialize the LCD
	
	//Initially the DS18B20 reports the temperature as 85.0000 degrees Centigrade (See datasheet)
	//So we need to put some delay for the temperature to stabilize.
	//By stabilize we mean two things:
	//1. The DS18S20's temperature output should stabilize (takes a few hundred milliseconds)
	//2. The temperature of the environment around the temperature sensor must stabilize. (This depends on the application, for 
	//   example if you are measuring the temperature of exhaust flowing through the vent, then you might need to
	//   wait for a few more seconds so that the blowers may start and the actual exhaust reaches the temperature sensor,
	//   and the temperature then recorded is that of the actual exhaust air.)
	for(i=0; i<= 25; i++)
	{
		DelayMs(200);
		temperature=get_temperature(tempstring);
		
		LCD_row1();
		LCD_gotoxy(0,0);
		LCD_putc('T');
		LCD_putc('=');
		LCD_puts(tempstring);
		LCD_putc(' ');
		LCD_putc(0xDF);			//Degree Symbol
		LCD_putc('C');
		
		LCD_row2();
		LCD_gotoxy(0,1);
		LCD_puts("Initializing...");
	}
	
	LCD_init();		//Clear the LCD before going into the Super-Loop
	
	while(1)
	{
		temperature=get_temperature(tempstring);
		
		LCD_row1();
		LCD_gotoxy(0,0);
		LCD_putc('T');
		LCD_putc('=');
		LCD_puts(tempstring);
		LCD_putc(' ');
		LCD_putc(0xDF);			//Degree Symbol
		LCD_putc('C');
		
		LCD_row2();
		LCD_puts("R1=");
		
		if(temperature >= RELAY1_TEMP)		//Actual logic to fire the relays as per the temperature and show the status on LCD
		{
			RELAY1_STATE = ON;
			LCD_puts("ON ");
		}
		else
		{
			RELAY1_STATE = OFF;
			LCD_puts("OFF");
		}
		
		LCD_puts("  R2=");
		
		if(temperature >= RELAY2_TEMP)
		{
			RELAY2_STATE = ON;
			LCD_puts("ON ");
		}
		else
		{
			RELAY2_STATE = OFF;
			LCD_puts("OFF");
		}
		
		DelayMs(200);
	}
}