Read DHT22 datasheet to understand what I'm going to do because every thing about the sensor is in its datasheet which can be downloaded from the following link:
DHT22 Datasheet
Required Components:
- PIC16F887 Microcontroller
- DHT22 or compatible Sensor
- 1602 LCD screen
- 10K Potentiometer
- 4.7K ohm resistor
- 0.1µF Ceramic capacitor (Optional but recommended)
- +5V Power source
- Breadboards
- Jumper wires
PIC16F887 Microcontroller with DHT22 digital sensor C code:
This is the C code of our example, it has been tested with CCS PIC C compiler version 5.051.
/* Interfacing PIC16F887 with DHT22 (AM2302) sensor CCS C code Read DHT22 datasheet to understand the code! Internal oscillator used @ 8MHz Timer1 is configured so that it increments every 1µs 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 <16F887.h> #fuses NOMCLR NOBROWNOUT NOLVP INTRC_IO #use delay(clock = 8MHz) #include <lcd.c> #use fast_io(B) #use fast_io(D) #define DHT22_PIN PIN_B0 // DHT22 Data pin is connected to RB0 char message1[] = "Temp = 00.0 C "; char message2[] = "RH = 00.0 % "; short Time_out = 0; unsigned int8 T_byte1, T_byte2, RH_byte1, RH_byte2, CheckSum ; unsigned int16 Temp, RH; void start_signal(){ output_drive(DHT22_PIN); // Configure connection pin as output output_low(DHT22_PIN); // Connection pin output low delay_ms(25); output_high(DHT22_PIN); // Connection pin output high delay_us(25); output_float(DHT22_PIN); // Configure connection pin as input } short check_response(){ set_timer1(0); // Set Timer1 value to 0 setup_timer_1(T1_INTERNAL | T1_DIV_BY_2); // Start Timer1 with internal clock source + 2 prescaler while(!input(DHT22_PIN) && get_timer1() < 100); // Wait until DHT22_PIN becomes high (cheking of 80µs low time response) if(get_timer1() > 99) // If response time > 99µS ==> Response error return 0; // Return 0 (Device has a problem with response) else{ set_timer1(0); // Set Timer1 value to 0 while(input(DHT22_PIN) && get_timer1() < 100); // Wait until DHT22_PIN becomes low (cheking of 80µs high time response) if(get_timer1() > 99) // If response time > 99µS ==> Response error return 0; // Return 0 (Device has a problem with response) else return 1; // Return 1 (response OK) } } unsigned int8 Read_Data(){ unsigned int8 i, _data = 0; if(Time_out) break; for(i = 0; i < 8; i++){ set_timer1(0); // Set Timer1 value to 0 while(!input(DHT22_PIN)) // Wait until DHT22_PIN becomes high if(get_timer1() > 100){ // If low time > 100 ==> Time out error (Normally it takes 50µs) Time_out = 1; break; } set_timer1(0); // Set Timer1 value to 0 while(input(DHT22_PIN)) // Wait until DHT22_PIN becomes low if(get_timer1() > 100){ // If high time > 100 ==> Time out error (Normally it takes 26-28µs for 0 and 70µs for 1) Time_out = 1; break; } if(get_timer1() > 50) // If high time > 50 ==> Sensor sent 1 bit_set(_data, (7 - i)); // Set bit (7 - i) } return _data; } void main(){ setup_oscillator(OSC_8MHZ); // Set the internal oscillator to 8MHz setup_timer_1(T1_DISABLED); // Disable Timer1 lcd_init(); // Initialize LCD module lcd_putc('\f'); // Clear LCD while(TRUE){ delay_ms(1000); // Wait 1s Time_out = 0; Start_signal(); // Send start signal to the sensor if(check_response()){ // Check if there is a response from sensor (If OK start reading humidity and temperature data) 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 setup_timer_1(T1_DISABLED); // Disable Timer1 if(Time_out) { // If there is a time out in reading lcd_putc('\f'); // LCD clear lcd_gotoxy(5, 1); // Go to column 5 row 1 lcd_putc("Time out!"); // Display "Time out!" } else { // If there is no time out 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; if(RH == 1000) // If the relative humidity = 100.0 % message2[6] = 1 + 48; else message2[6] = ' '; message2[7] = (RH / 100) % 10 + 48; message2[8] = (RH / 10) % 10 + 48; message2[10] = RH % 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 { // If there is no response from DHT22 sensor 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"); } } }The following video shows simulation using Proteus of PIC16F887 and DHT22 sensor:
C Code, HEX file and simulation files can be downloaded from this link:
Simulation Download
