Interfacing DHT11 relative humidity and temperature sensor with PIC16F877A microcontroller

 

This topic shows how to interface PIC16F877A microcontroller with DHT11 digital relative humidity and temperature sensor using CCS PIC C compiler.
The following topic shows how the DHT11 sensor works and how to simulate it with PIC16F877A using Proteus software.
Interfacing PIC16F877A with DHT11 (RHT01) sensor Proteus simulation

To see how the DHT11 works just read the previous topic and the sensor datasheet.
Interfacing PIC16F877A with DHT11 sensor circuit:

The circuit is simple, there is the microcontroller PIC16F877A, DHT11 sensor and 1602 LCD to display humidity and temperature results.
The DHT11 sensor has 4 pins:
VCC : Positive power supply (+5V)
DATA : Sensor data input and output
NC : Not connected terminal
GND : Ground (0V)
A pull-up resistor must be added between the DHT11 data pin and VCC (+5V) pin as shown in the circuit schematic (4.7K ~ 10K).
Interfacing PIC16F877A with DHT11 humidity and temperature sensor CCS C code:
The interfacing code is written using CCS PIC C compiler PCWHD version 5.051.
If you want to understand the code please read the DHT11 datasheet.
Variables Time_out and k are used to test reading time to avoid wrong data reception and microcontroller hanging.

// Interfacing PIC16F877A with DHT11 sensor CCS C code
// http://ccspicc.blogspot.com/
// electronnote@gmail.com

//LCD module connections
#define LCD_RS_PIN PIN_D0
#define LCD_RW_PIN PIN_D1
#define LCD_ENABLE_PIN PIN_D2
#define LCD_DATA4 PIN_D3
#define LCD_DATA5 PIN_D4
#define LCD_DATA6 PIN_D5
#define LCD_DATA7 PIN_D6
//End LCD module connections

#include <16F877A.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP                       
#use delay(clock = 8000000)
#include <lcd.c>
#use fast_io(B)
#define DHT11_PIN PIN_B4                // Connection pin between DHT11 and mcu

char message1[] = "Temp = 00.0 C  ";
char message2[] = "RH   = 00.0 %  ";
short Time_out;
unsigned int8 T_byte1, T_byte2, RH_byte1, RH_byte2, CheckSum ;
void start_signal(){
  output_drive(DHT11_PIN);              // Configure connection pin as output
  output_low(DHT11_PIN);                // Connection pin output low
  delay_ms(25);
  output_high(DHT11_PIN);               // Connection pin output high
  delay_us(30);
  output_float(DHT11_PIN);              // Configure connection pin as input
}
short check_response(){
  delay_us(40);
  if(!input(DHT11_PIN)){                // Read and test if connection pin is low
    delay_us(80);
    if(input(DHT11_PIN)){               // Read and test if connection pin is high
      delay_us(50);
      return 1;
    }
  }
}
unsigned int8 Read_Data(){
  unsigned int8 i, k, _data = 0;        // k is used to count 1 bit reading duration
  if(Time_out)
    break;
  for(i = 0; i < 8; i++){
    k = 0;
    while(!input(DHT11_PIN)){           // Wait until DHT11 pin get raised
      k++;
      if(k > 100){
        Time_out = 1;
        break;
      }
      delay_us(1);
    }
    delay_us(30);
    if(!input(DHT11_PIN))
      bit_clear(_data, (7 - i));        // Clear bit (7 - i)
    else{
      bit_set(_data, (7 - i));          // Set bit (7 - i)
      while(input(DHT11_PIN)){          // Wait until DHT11 pin goes low
        k++;
        if(k > 100){
        Time_out = 1;
        break;
      }
      delay_us(1);}
    }
  }
  return _data;
}
void main(){
  lcd_init();                                 // Initialize LCD module
  lcd_putc('\f');                             // LCD clear
  delay_ms(1000);
  while(TRUE){
    Time_out = 0;
    Start_signal();
    if(check_response()){                     // If there is a response from sensor
      RH_byte1 = Read_Data();                 // read RH byte1
      RH_byte2 = Read_Data();                 // read RH byte2
      T_byte1 = Read_Data();                  // read T byte1
      T_byte2 = Read_Data();                  // read T byte2
      Checksum = Read_Data();                 // read checksum
      if(Time_out){                           // If reading takes long time
        lcd_putc('\f');                       // LCD clear
        lcd_gotoxy(5, 1);                     // Go to column 5 row 1
        lcd_putc("Time out!");
      }
      else{
       if(CheckSum == ((RH_Byte1 + RH_Byte2 + T_Byte1 + T_Byte2) & 0xFF)){
         message1[7]  = T_Byte1/10  + 48;
         message1[8]  = T_Byte1%10  + 48;
         message1[10] = T_Byte2/10  + 48;
         message2[7]  = RH_Byte1/10 + 48;
         message2[8]  = RH_Byte1%10 + 48;
         message2[10] = RH_Byte2/10 + 48;
         message1[11] = 223;                   // Degree symbol
         lcd_gotoxy(1, 1);                     // Go to column 1 row 1
         printf(lcd_putc, message1);           // Display message1
         lcd_gotoxy(1, 2);                     // Go to column 1 row 2
         printf(lcd_putc, message2);           // Display message2
       }
       else{
         lcd_putc('\f');                       // LCD clear
         lcd_gotoxy(1, 1);                     // Go to column 1 row 1
         lcd_putc("Checksum Error!");
       }
      }
    }
    else {
      lcd_putc('\f');                          // LCD clear
      lcd_gotoxy(3, 1);                        // Go to column 3 row 1
      lcd_putc("No response");
      lcd_gotoxy(1, 2);                        // Go to column 1 row 2
      lcd_putc("from the sensor");
    }
  delay_ms(1000);
  }
}

PIC16F877A with DHT11 relative humidity and temperature sensor video:
The following video shows the project circuit connected in a breadboard.