Interfacing PIC16F877A with DHT22(Temperature and Humidity Sensor )

Description:

These sensors are very popular for electronics hobbyists because there are very cheap but still providing great performance.The DHT22 is the more expensive version which obviously has better specifications. Its temperature measuring range is from -40 to +125 degrees Celsius with +-0.5 degrees accuracy,DHT22 sensor has better humidity measuring range, from 0 to 100% with 2-5% accuracy

Specification:

Model-: AM2303 

Power supply-: 3.3-6V DC 

Output signal-: digital signal via single-bus 

Sensing element-: Polymer humidity capacitor & DS18B20 for detecting temperature 

Measuring range-: humidity 0-100%RH; temperature -40~125Celsius

Accuracy humidity-: +-2%RH(Max +-5%RH); temperature +-0.2Celsius 

Resolution or sensitivity-: humidity 0.1%RH; temperature 0.1Celsius 

Repeatability-: humidity +-1%RH; temperature +-0.2Celsius 

Humidity hysteresis--: +-0.3%RH 

Long-term Stability--: +-0.5%RH/year 

Sensing period-: Average: 2s 

Interchangeability-: fully interchangeable

Circuit Diagram:

MikroC Code:

//Interfacing PIC16F877A with DHT22

//Crystal used @ 12MHz

 sbit LCD_RS at RB0_bit;

 sbit LCD_EN at RB1_bit;

 sbit LCD_D4 at RB2_bit;

 sbit LCD_D5 at RB3_bit;

 sbit LCD_D6 at RB4_bit;

 sbit LCD_D7 at RB5_bit;

 sbit LCD_RS_Direction at TRISB0_bit;

 sbit LCD_EN_Direction at TRISB1_bit;

 sbit LCD_D4_Direction at TRISB2_bit;

 sbit LCD_D5_Direction at TRISB3_bit;

 sbit LCD_D6_Direction at TRISB4_bit;

 sbit LCD_D7_Direction at TRISB5_bit;

 // End LCD module connections

 unsigned char  Check, T_byte1, T_byte2, RH_byte1, RH_byte2, Ch ;

 unsigned Temp, RH, Sum ;

 unsigned be, me,ne, Sum2,h1,h2 ;

//////////////////////////////

 void StartSignal(){

 TRISD.F0 = 0;    //Configure RD0 as output

 PORTD.F0 = 0;    //RD0 sends 0 to the sensor

 delay_ms(18);

 PORTD.F0 = 1;    //RD0 sends 1 to the sensor

 delay_us(30);

 TRISD.F0 = 1;    //Configure RD0 as input

  }

 //////////////////////////////

 void CheckResponse(){

 Check = 0;

 delay_us(40);

 if (PORTD.F0 == 0){

 delay_us(80);

 if (PORTD.F0 == 1)   Check = 1;   delay_us(40);}

 }

 //////////////////////////////

 char ReadData(){

 char i, j;

 for(j = 0; j < 8; j++){

 while(!PORTD.F0); //Wait until PORTD.F0 goes HIGH

 delay_us(30);

 if(PORTD.F0 == 0)

       i&= ~(1<<(7 - j));  //Clear bit (7-b)

 else {i|= (1 << (7 - j));  //Set bit (7-b)

 while(PORTD.F0);}  //Wait until PORTD.F0 goes LOW

 }

 return i;

 }

 //////////////////////////////

 void main() {

 TRISC = 0;    //Configure RC0 as output

 Lcd_Init();

 Lcd_Cmd(_LCD_CURSOR_OFF);        // cursor off

 Lcd_Cmd(_LCD_CLEAR);             // clear LCD

 while(1){

  StartSignal();

  CheckResponse();

  if(Check == 1){

  RH_byte1 = ReadData();

  RH_byte2 = ReadData();

  T_byte1 = ReadData();

  T_byte2 = ReadData();

  Sum = ReadData();

  if(Sum == ((RH_byte1+RH_byte2+T_byte1+T_byte2) & 0XFF)){

  Temp = T_byte1;

  Temp = (Temp << 8) | T_byte2;

  RH = RH_byte1;

  Lcd_Cmd(_LCD_CLEAR);             // clear LCD

  RH = (RH << 8) | RH_byte2;

  Lcd_Out(1, 6, "Temp:   . C");

  Lcd_Out(2, 2, "Humidity:   . %");

  if (Temp > 0X8000){

  Lcd_Out(1, 11, "-");

  Temp = Temp & 0X7FFF; }

  be=(48 + ((Temp / 100) % 10));//work for frist later of temperature like 2 than 22,,23,

  LCD_Chr(1, 12, be);

  me= (48 + ((Temp / 10) % 10));

  LCD_Chr(1, 13, me);

  ne=48 + (Temp % 10);

  LCD_Chr(1, 15, ne); //after (.) number 

 

 //for humidity

  h1=  48 + ((RH / 100) % 10);

  LCD_Chr(2, 12, h1);

  h2= 48 + ((RH / 10) % 10);

  LCD_Chr(2, 13, h2);

  LCD_Chr(2, 15, 48 + (RH % 10));

  /////////////////////////////////////////////////

    if(be==51 & me==55 & ne>53){ // more then 26*C   relay 

    DELAY_MS(500);

     portc.f0=0;

      }

    if(be<52 & me<56 & ne<52 ){  // less then 26*C

     portc.f0=1;

    }

    if (h1>53 & h2>52)  // for humidity control relay 

    {

    portc.f1 =0;

    }

    if(h1<54 & h2<49)

    {

    portc.f1=1;

    }

   }

  else {

  Lcd_Cmd(_LCD_CURSOR_OFF);        // cursor off

  Lcd_Cmd(_LCD_CLEAR);             // clear LCD

  Lcd_Out(1, 1, "Check sum error");}

  }

  else {

  Lcd_Out(1, 3, "No response");

  Lcd_Out(2, 1, "from the sensor");

  }

  delay_ms(1000);

  }

  }