Interface PIC16F84A microcontroller with DHT22(AM2302 - RHT03) relative humidity and temperature sensor
This topic shows how to interface PIC16F84A microcontroller with DHT22 sensor with hardware circuit.Related topic:
The following topic shows PIC16F84A microcontroller and DHT22 Proteus simulation and some details about this sensor.
PIC16F84A + DHT22(AM2302, RHT03) sensor Proteus simulation
Interfacing PIC16F84A with DHT22 circuit:
The following image shows project circuit schematic.
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 PIC16F84A with DHT22(AM2302,RHT03) sensor CCS C code // http://ccspicc.blogspot.com/ // electronnote@gmail.com //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 <16F84A.h> #fuses HS,NOWDT,PUT,NOPROTECT #use delay(clock = 8000000) #include <lcd.c> #use fast_io(A) // Connection pin between PIC16F84A and DHT22 sensor #BIT Data_Pin = 0x05.0 // Pin mapped to PORTA.0 #BIT Data_Pin_Direction = 0x85.0 // Pin direction mapped to TRISA.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 PIC16F84A with DHT22 sensor video:
The following video shows hardware circuit of this project.
