Question

Design a digital temperature meter using one temperature sensor

Answer 1

Temperature Indicator

In the preented circuit diagram, Thermister is used to measure the temperature, Thje thermister is connected at connector (J3).

A LCD is also connected to show the temperature on LCD.

The design is around PIC16F877A microcontroller. This design also controls the heating and cooling using the two relays as Relay-1 and Relay-2.

The working code for the same is given below:

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#define SET_POINT_WINTER_LOW_L   0x00

#define SET_POINT_WINTER_LOW_H   0x01

#define SET_POINT_WINTER_HIGH_L 0x02

#define SET_POINT_WINTER_HIGH_H 0x03

#define SET_POINT_SUMMER_LOW_L   0x04

#define SET_POINT_SUMMER_LOW_H   0x05

#define SET_POINT_SUMMER_HIGH_L 0x06

#define SET_POINT_SUMMER_HIGH_H 0x07

#define ADDRESS_SEASON           0x08

#define WINTER                 0

#define SUMMER                 1

#define DISPLAY_FREQ           25000

#define FLIP_DISP_FREQ         1000

#define BOUNCE_DELAY           200

#define LED_ON                 0

#define LED_OFF                1

#define EEPROM_DELAY           200

/* Time delay for LCD On time*/

#define LCD_ON_TIME            40

unsigned char SetPoint_Winter_Low_L=0,SetPoint_Winter_Low_H=0;

unsigned char SetPoint_Winter_High_L=0,SetPoint_Winter_High_H=0;

unsigned char SetPoint_Summer_Low_L=0,SetPoint_Summer_Low_H=0;

unsigned char SetPoint_Summer_High_L=0,SetPoint_Summer_High_H=0;

unsigned char Season=WINTER;

unsigned int CurrentTemp,SetPoint_High,SetPoint_Low;

unsigned int ADCVal=0;

unsigned int DisplayCount=0;

//sbit RL_CH_TEMP at RE0_bit;

//sbit RL_CH_TEMP_Direction at TRISE0_bit;

//sbit RL_CC at RA5_bit;

sbit RL_CH at RA5_bit;      //Heatin Relay

sbit RL_CH_Direction at TRISA5_bit;

sbit RL_CC at RE0_bit;     //Cooling Relay

sbit RL_CC_Direction at TRISE0_bit;

// Lcd pinout settings

sbit LCD_RS at RC5_bit;

//sbit LCD_CHECK at RD2_bit;

sbit LCD_EN at RC7_bit;

sbit LCD_D7 at RD7_bit;

sbit LCD_D6 at RD6_bit;

sbit LCD_D5 at RD5_bit;

sbit LCD_D4 at RD4_bit;

sbit LED_H at RB4_bit;

sbit LED_C at RB5_bit;

sbit LED_H_Direction at TRISB4_bit;

sbit LED_C_Direction at TRISB5_bit;

sbit SW_1 at RB0_bit;

sbit SW_2 at RB1_bit;

// Pin direction

sbit LCD_POWER at RB2_bit;

sbit LCD_POWER_Direction at TRISB2_bit;

sbit LCD_RS_Direction at TRISC5_bit;

//sbit LCD_CHECK_Direction at TRISD2_bit;

sbit LCD_EN_Direction at TRISC7_bit;

sbit LCD_D7_Direction at TRISD7_bit;

sbit LCD_D6_Direction at TRISD6_bit;

sbit LCD_D5_Direction at TRISD5_bit;

sbit LCD_D4_Direction at TRISD4_bit;

void DisplayWinterSetPoints(void);

void DisplaySummerSetPoints(void);

void FaultCondition(void);

void EditSeason(void);

const code unsigned int Res_1[] = {

28160,

26920,

25760,

24650,

23600,

22600,

20740,

19870,

19050,

18270,

17510,

16800,

16120,

15470,

14850,

14260,

13700,

13160,

12640,

12160,

11680,

11230,

10800,

10390,

10000,

9624 ,

9265 ,

8921 ,

8591 ,

8276 ,

7973 ,

7684 ,

7406 ,

7140 ,

6885 ,

6641 ,

6406 ,

6181 ,

5965 ,

5758 ,

5559 ,

5368 ,

5185 ,

5008 ,

4839 ,

4676 ,

4520 ,

4370 ,

4225 ,

4086 ,

3953 ,

3824 ,

3700 ,

3581 ,

3467 ,

3356 ,

3250 ,

3147 ,

3049 ,

2954 ,

2862 ,

2774 ,

2689 ,

2607 ,

2528 ,

2451 ,

2378 ,

2306 ,

2238 ,

2172 ,

2108 ,

2046 ,

1986 ,

1929 ,

1873 ,

1820 ,

1768 ,

1717 ,

1669 ,

1622 ,

1577 ,

1533 ,

1490 ,

1449 ,

1410 ,

1371 ,

1334 ,

1298 ,

1263 ,

1229 ,

1197 ,

1165 ,

1134 ,

1105 ,

1076 ,

1048 ,

1021 ,

995 ,

969 ,

945 ,

};

unsigned char EditSetPoints(unsigned char EditData)

{

unsigned char FlagEdit=1,tempEditData;

tempEditData = EditData;

while(FlagEdit)

{

Lcd_Chr(2,8,0x30+(EditData/10));

Lcd_Chr(2,9,0x30+(EditData%10));

if(SW_1==0) {Delay_ms(BOUNCE_DELAY);tempEditData=tempEditData+1;if(tempEditData>50) tempEditData=0;}

if(SW_2==0) FlagEdit=0;

}

return(tempEditData);

}

void FaultCondition(void)

{

    Lcd_Out(1,1,"      FAULT     ");

    Lcd_Out(2,1,"   SENSOR OPEN ");

    RL_CH=0;

    RL_CC=0;

    LED_H=~LED_H;

    LED_C = LED_OFF;

    Delay_ms(500);

}

void EditSeason(void)

{

if(Season==WINTER) Season = SUMMER;

else               Season = WINTER;

                     Lcd_Out(1,1,"SEASON CHANGED..");

if(Season==WINTER) Lcd_Out(2,1,"NOW -> WINTER   ");

if(Season==SUMMER) Lcd_Out(2,1,"NOW -> SUMMER   ");

while(SW_1==0){} Delay_ms(500);

}

void MakeLCDOff(void)

{

Lcd_Cmd(_LCD_CLEAR);               // Clear display

LCD_POWER=0;

}

unsigned int LCDDisplayCount=0;

void MakeLCDON(void)

{

LCD_POWER=1;

LCDDisplayCount=0;

Lcd_Init();

Lcd_Cmd(_LCD_CLEAR);               // Clear display

Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

}

void main(void)

{

unsigned int TempChar,FinalTemperature,TResistance,Tempt=0,FlipDispCount=0;

unsigned char Flag=1,dCnt,EditCount=0,Flip=1,Error=0,FlagUp=0,FlagDown=0,H=0,C=0,FlagIO=0,y_1=0,y_2=0;

unsigned long CountEditSeason=0,DisplayONCount=0;

unsigned char FlagDisplaySetPoints=1,FlagSeason=WINTER,FlagH=0,FlagC=0,FlipDisplay=1,FirstTimeFlag=1;

unsigned long Temp,Qt,Rem,Tr;

signed char TempDir=1,TempPrev=0,TempCurrent=0;

TRISE = 0x00;

TRISD=0x00;

TRISC=0x00;

TRISB = 0x03;

TRISA = 0x0F;

ADC_Init();

LCD_POWER=1;

Lcd_Init();

Lcd_Cmd(_LCD_CLEAR);               // Clear display

Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

RL_CH=0; RL_CC=0; //Both Relay OFF

DisplayCount=DISPLAY_FREQ;

SetPoint_Winter_Low_L = 17;// = EEPROM_Read(SET_POINT_WINTER_LOW); Delay_ms(EEPROM_DELAY);

SetPoint_Winter_Low_H = 19;//High = EEPROM_Read(SET_POINT_WINTER_HIGH); Delay_ms(EEPROM_DELAY);

SetPoint_Winter_High_L = 21;// = EEPROM_Read(SET_POINT_WINTER_LOW); Delay_ms(EEPROM_DELAY);

SetPoint_Winter_High_H = 23;//High = EEPROM_Read(SET_POINT_WINTER_HIGH); Delay_ms(EEPROM_DELAY);

SetPoint_Summer_Low_L = 19;// = EEPROM_Read(SET_POINT_WINTER_LOW); Delay_ms(EEPROM_DELAY);

SetPoint_Summer_Low_H = 21;//High = EEPROM_Read(SET_POINT_WINTER_HIGH); Delay_ms(EEPROM_DELAY);

SetPoint_Summer_High_L = 23;// = EEPROM_Read(SET_POINT_WINTER_LOW); Delay_ms(EEPROM_DELAY);

SetPoint_Summer_High_H = 25;//High = EEPROM_Read(SET_POINT_WINTER_HIGH); Delay_ms(EEPROM_DELAY);

Season = EEPROM_Read(ADDRESS_SEASON);                      Delay_ms(EEPROM_DELAY);

if(Season!=WINTER && Season!=SUMMER) {Season = WINTER;}

// Season = WINTER;

while(1)

{

if(DisplayCount>=DISPLAY_FREQ)

{

   TempPrev = TempCurrent;

   if(LCDDisplayCount < LCD_ON_TIME) LCDDisplayCount++;

   if(LCDDisplayCount >= LCD_ON_TIME) MakeLCDOff();//LCD_POWER=0;

   FlipDispCount++;

   if(FlipDispCount >= FLIP_DISP_FREQ) {FlipDisplay=1-FlipDisplay; FlipDispCount=0;}

   DisplayCount=0;

   Flag=1;

   Temp = ADC_Read(0);

   if(Temp < 950)

   {

    LED_H = LED_OFF;

    Error=0;

    Qt = ((Temp *10)/(1024 - Temp))*1000;

    Rem = (Temp *10)%(1024 - Temp);

    Tr = Qt + Rem;

    if(FlipDisplay)

    {

     if(Season==SUMMER) {Lcd_Out(1,1,"SUMMER (HIGH)");}

     else               {Lcd_Out(1,1,"WINTER (LOW) ");}

     Lcd_Out(2,1,"COACH TEMP=    C");

     y_1=2;

    }

    else

    {

     Lcd_Out(1,1,"COACH TEMP=    C");

     y_1=1;

    }

    for(dCnt=0;(dCnt < 99 && Flag==1);dCnt=dCnt+1)

    {

     if(Flag==1 && Tr > Res_1[dCnt+1] && Tr <= Res_1[dCnt])

     {

      Flag=0;

      FinalTemperature = dCnt+1;

     }

    }                                       

    if(TempDir!=0)

    {

     Lcd_Chr(y_1,15,0xDF);

     TempChar = 0x30 + (FinalTemperature/10); Lcd_Chr(y_1,13,TempChar);

     TempChar = 0x30 + (FinalTemperature%10); Lcd_Chr(y_1,14,TempChar);

    }

   

//    TempChar = 0x30 + (LCDDisplayCount/10); Lcd_Chr(1,15,TempChar);

//    TempChar = 0x30 + (LCDDisplayCount%10); Lcd_Chr(1,16,TempChar);

    TempCurrent = FinalTemperature;

    TempDir = TempCurrent - TempPrev;

   }

   else

   {

    MakeLCDON();

    FaultCondition();

    Error=1;

    LED_H=LED_OFF;

    Lcd_Cmd(_LCD_CLEAR);               // Clear display

    Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

   }

}

DisplayCount++;

if(Error==0)

{

if(Season==WINTER)

{

   if(FinalTemperature >= 23                                         )   C=1;

   if(FinalTemperature > 21 && FinalTemperature < 23 && TempDir < 0)   C=1;

   if(FinalTemperature <= 21                           && TempDir < 0)   C=0;

   if(FinalTemperature > 21 && FinalTemperature < 23 && TempDir > 0)   C=0;

   if(FinalTemperature <= 17                                         )   H=1;

   if(FinalTemperature > 17 && FinalTemperature < 19 && TempDir > 0)   H=1;

   if(FinalTemperature >= 19                                         )   H=0;

   if(FinalTemperature > 17 && FinalTemperature < 19 && TempDir < 0)   H=0;

   if(H) {RL_CH=1; RL_CC=0;}

   if(C) {RL_CH=0; RL_CC=1;}

   if(H==0 && C==0) {RL_CH=0; RL_CC=0;}

}

if(Season==SUMMER)

{

   if(FinalTemperature >= 25                                         )   C=1;

   if(FinalTemperature > 23 && FinalTemperature < 25 && TempDir < 0)   C=1;

   if(FinalTemperature <= 23                                         )   C=0;

   if(FinalTemperature <= 19                                         )   H=1;

   if(FinalTemperature > 19 && FinalTemperature < 21 && TempDir > 0)   H=1;

   if(FinalTemperature >= 21                                         )   H=0;

   if(FinalTemperature > 19 && FinalTemperature < 21 && TempDir < 0)   H=0;

   if(H) {RL_CH=1; RL_CC=0;}

   if(C) {RL_CH=0; RL_CC=1;}

   if(H==0 && C==0) {RL_CH=0; RL_CC=0;}

}

if(!FlipDisplay)

{

   if(H==1 && C==0) Lcd_Out(2,1,"Htr-ON   AC-OFF");

   if(H==0 && C==1) Lcd_Out(2,1,"Htr-OFF   AC-ON");

   if(H==0 && C==0) Lcd_Out(2,1,"Htr-OFF AC-OFF");

}

if(SW_1==0)

{

   MakeLCDON();

   FlagDisplaySetPoints=1;

   Delay_ms(BOUNCE_DELAY);

   Flip=1-Flip;

   Lcd_Cmd(_LCD_CLEAR);               // Clear display

   Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

   if(Flip==1)    DisplayWinterSetPoints();

   if(Flip==0)    DisplaySummerSetPoints();

   while(FlagDisplaySetPoints)

   {

   CountEditSeason=0;

   if(SW_1==0)

     {

      Delay_ms(BOUNCE_DELAY);

      while(SW_1==0)

      {

       CountEditSeason++;

       if(CountEditSeason>100000)

       {

        EditSeason();

        EEPROM_Write(ADDRESS_SEASON,Season); Delay_ms(EEPROM_DELAY);

       }

      }

      FlagDisplaySetPoints=0;

     }

     else

     {

     Delay_ms(1500);   FlagDisplaySetPoints=0;

     }

   }

   Lcd_Cmd(_LCD_CLEAR);               // Clear display

   Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

   DisplayCount=DISPLAY_FREQ;

}

/*

if(SW_2==0)

{

   Delay_ms(BOUNCE_DELAY);

   if(EditCount==0)

   {

    SetPoint_Winter_Low_L = EditSetPoints(SetPoint_Winter_Low_L);

    EEPROM_Write(SET_POINT_WINTER_LOW_L,SetPoint_Winter_Low_L); Delay_ms(EEPROM_DELAY);

   }

   if(EditCount==1)

   {

    SetPoint_Winter_Low_H = EditSetPoints(SetPoint_Winter_Low_H);

    EEPROM_Write(SET_POINT_WINTER_LOW_H,SetPoint_Winter_Low_H); Delay_ms(EEPROM_DELAY);

   }

   if(EditCount==2)

   {

    SetPoint_Winter_High_L = EditSetPoints(SetPoint_Winter_High_L);

    EEPROM_Write(SET_POINT_WINTER_HIGH_L,SetPoint_Winter_High_L); Delay_ms(EEPROM_DELAY);

   }

   if(EditCount==3)

   {

    SetPoint_Winter_High_H = EditSetPoints(SetPoint_Winter_High_H);

    EEPROM_Write(SET_POINT_WINTER_HIGH_H,SetPoint_Winter_High_H); Delay_ms(EEPROM_DELAY);

   }

   if(EditCount==4)

   {

    SetPoint_Summer_Low_L = EditSetPoints(SetPoint_Summer_Low_L);

  EEPROM_Write(SET_POINT_SUMMER_LOW_L,SetPoint_Summer_Low_L); Delay_ms(EEPROM_DELAY);

   }

   if(EditCount==5)

   {

    SetPoint_Summer_Low_H = EditSetPoints(SetPoint_Summer_Low_H);

    EEPROM_Write(SET_POINT_SUMMER_LOW_H,SetPoint_Summer_Low_H); Delay_ms(EEPROM_DELAY);

   }  

   if(EditCount==6)

   {

    SetPoint_Summer_High_L = EditSetPoints(SetPoint_Summer_High_L);

    EEPROM_Write(SET_POINT_SUMMER_HIGH_L,SetPoint_Summer_High_L); Delay_ms(EEPROM_DELAY);

   }

   if(EditCount==7)

   {

    SetPoint_Summer_High_H = EditSetPoints(SetPoint_Summer_High_H);

    EEPROM_Write(SET_POINT_SUMMER_HIGH_H,SetPoint_Summer_High_H); Delay_ms(EEPROM_DELAY);

   }

   EditCount=EditCount+1;

   if(EditCount>7) EditCount=0;

   DisplayCount=DISPLAY_FREQ;

}

*/

}

}

}

void DisplayWinterSetPoints(void)

{

    Lcd_Out(1,1,"WINTER:");

    Lcd_Chr(1,9, 0x30+(SetPoint_Winter_Low_L/10));

    Lcd_Chr(1,10,0x30+(SetPoint_Winter_Low_L%10));

    Lcd_Chr(1,14,0x30+(SetPoint_Winter_Low_H/10));

    Lcd_Chr(1,15,0x30+(SetPoint_Winter_Low_H%10));

    Lcd_Chr(2,9, 0x30+(SetPoint_Winter_High_L/10));

    Lcd_Chr(2,10,0x30+(SetPoint_Winter_High_L%10));

    Lcd_Chr(2,14,0x30+(SetPoint_Winter_High_H/10));

    Lcd_Chr(2,15,0x30+(SetPoint_Winter_High_H%10));

}

void DisplaySummerSetPoints(void)

{

    Lcd_Out(1,1,"SUMMER:");

    Lcd_Chr(1,9, 0x30+(SetPoint_Summer_Low_L/10));

    Lcd_Chr(1,10,0x30+(SetPoint_Summer_Low_L%10));

    Lcd_Chr(1,14,0x30+(SetPoint_Summer_Low_H/10));

    Lcd_Chr(1,15,0x30+(SetPoint_Summer_Low_H%10));

    Lcd_Chr(2,9, 0x30+(SetPoint_Summer_High_L/10));

    Lcd_Chr(2,10,0x30+(SetPoint_Summer_High_L%10));

    Lcd_Chr(2,14,0x30+(SetPoint_Summer_High_H/10));

    Lcd_Chr(2,15,0x30+(SetPoint_Summer_High_H%10));

}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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