Interfacing PIC16F877A with DHT22(AM2302-RHT03) sensor using CCS PIC C




Interfacing PIC16F877A with DHT22(AM2302-RHT03) digital humidity and temperature sensor
Interfacing PIC16F877A with DHT22(AM2302-RHT03) sensor using CCS PIC C
This topic shows how to interface PIC16F877A microcontroller with DHT22 sensor with hardware circuit.
Related topic:
The following topic shows PIC16F877A microcontroller and DHT22 Proteus simulation and some details about this sensor.
PIC16F877A and DHT22(AM2302, RHT03) sensor Proteus simulation
Interfacing PIC16F877A with DHT22(AM2302, RHT03) sensor circuit:
The following circuit schematic shows complete project circuit.Circuit Interfacing PIC16F877A with DHT22(AM2302-RHT03) sensor using CCS PIC C
The circuit is simple, there is the microcontroller PIC16F877A, DHT22 sensor and 1602 LCD to display humidity and temperature results.
Interfacing PIC16F877A with DHT22(AM2302, RHT03) sensor CCS C code:
The interfacing code is written with CCS PIC C compiler PCWHD version 5.051.
If you want to understand the code please read the DHT22 datasheet.
Variables Time_out and k are used to test reading time to avoid wrong data reception or microcontroller hanging.

// Interfacing PIC16F877A with DHT22(AM2302-RHT03) sensor CCS C code
// http://ccspicc.blogspot.com/
// [email protected]
//LCD module connections
#define LCD_RS_PIN PIN_B0
#define LCD_RW_PIN PIN_B1
#define LCD_ENABLE_PIN PIN_B2
#define LCD_DATA4 PIN_B3
#define LCD_DATA5 PIN_B4
#define LCD_DATA6 PIN_B5
#define LCD_DATA7 PIN_B6
//End LCD module connections
#include <16F877A.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP                       
#use delay(clock = 8000000)
#include <lcd.c>
#use fast_io(D)
// Connection pin between PIC16F877A and DHT22 sensor
#BIT Data_Pin = 0x08.0                       // Pin mapped to PORTD.0
#BIT Data_Pin_Direction = 0x88.0             // Pin direction mapped to TRISD.0
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 ;
unsigned int16 Temp, RH;
void start_signal(){
  Data_Pin_Direction = 0;              // Configure connection pin as output
  Data_Pin = 0;                        // Connection pin output low
  delay_ms(25);
  Data_Pin = 1;                        // Connection pin output high
  delay_us(30);
  Data_Pin_Direction = 1;              // Configure connection pin as input
}
short check_response(){
  delay_us(40);
  if(!Data_Pin){                     // Read and test if connection pin is low
    delay_us(80);
    if(Data_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(!Data_Pin){                          // Wait until pin goes high
      k++;
      if (k > 100) {Time_out = 1; break;}
      delay_us(1);}
    delay_us(30);
    if(!Data_Pin)
      bit_clear(_data, (7 - i));               // Clear bit (7 - i)
    else{
      bit_set(_data, (7 - i));                 // Set bit (7 - i)
      while(Data_Pin){                         // Wait until 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 
  while(TRUE){
    delay_ms(1000);
    Time_out = 0;
    Start_signal();
    if(check_response()){                    // If there is 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)){
        RH = RH_byte1;
        RH = (RH << 8) | RH_byte2;
        Temp = T_byte1;
        Temp = (Temp << 8) | T_byte2;
        if (Temp > 0X8000){
         message1[6] = '-';
         Temp = Temp & 0X7FFF; }
        else
         message1[6] = ' ';
        message1[7]  = (Temp / 100) % 10  + 48;
        message1[8]  = (Temp / 10) % 10  + 48;
        message1[10] = Temp % 10  + 48;
        message2[7]  = (RH / 100) % 10 + 48;
        message2[8]  = (RH / 10) % 10 + 48;
        message2[10] = RH % 10 + 48;
        message1[11] = 223;                   // Degree symbol
        lcd_putc('\f');                       // LCD clear    
        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");
    }
  }
}

Interfacing PIC16F877A with DHT22 sensor video:
The following video shows hardware circuit of this project.

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