Comparison between DHT11 (RHT01) and DHT22 (AM2302 - RHT03) sensors
The following two topic shows how to interface PIC16F877A with DHT11 and DHT22 sensors respectively:
Interfacing DHT11 relative humidity and temperature sensor with PIC16F877A microcontroller
Interfacing PIC16F877A with DHT22(AM2302-RHT03) sensor using CCS PIC C
The following table shows the DHT11 sensor characteristics (from DHT11 datasheet):
| DHT11 | DHT22 | |
| Relative Humidity Operating Range | 20 ~ 90% | 0 ~ 100% |
| Relative Humidity Accuracy | ±5%RH | ±2%RH (Max ±5%RH) |
| Humidity Resolution | 1%RH | 0.1%RH |
| Humidity Repeatability | ±1%RH | ±1%RH |
| Humidity Hysteresis | ±1%RH | ±0.3%RH |
| Long-term Stability | ±1%RH/year | ±0.5%RH/year |
| Temperature Operating Range | 0 ~ 50°C | -40 ~ 80°C |
| Temperature Accuracy | ±2°C | ±0.5°C |
| Temperature Resolution | 1°C | 0.1°C |
DHT11 and DHT22 interfacing with PIC16F877A microcontroller:
The following circuit schematic shows the comparison between DHT11 and DHT22 sensors connection circuit.
The sensor DHT11 as well as DHT22 has 4 pins which are:
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 data pin of each sensor and VCC (+5V) pin as shown in the circuit schematic (4.7K ~ 10K).
2004 (20x4) LCD display is used to display temperature and humidity results for both sensors.
CCS C code for DHT11 vs DHT22 project:
The comparison between DHT11 and DHT22 (AM2302) sensors full CCS C code is below.
// DHT11 VS DHT22 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_B4 // Connection pin between DHT11 and mcu #define DHT22 PIN_B5 // Connection pin between DHT22 and mcu char message1[] = "DHT11 Temp = 00.0 C "; char message2[] = "DHT11 RH = 00.0 % "; char message3[] = "DHT22 Temp = 00.0 C "; char message4[] = "DHT22 RH = 00.0 % "; short Time_out; unsigned int8 T_byte1, T_byte2, RH_byte1, RH_byte2, CheckSum ; unsigned int16 Temp, RH; void dht11_start_signal(){ output_drive(DHT11); // Configure connection pin as output output_low(DHT11); // Connection pin output low delay_ms(25); output_high(DHT11); // Connection pin output high delay_us(30); output_float(DHT11); // Configure connection pin as input } short dht11_check_response(){ delay_us(40); if(!input(DHT11)){ // Read and test if connection pin is low delay_us(80); if(input(DHT11)){ // Read and test if connection pin is high delay_us(50); return 1; } } } unsigned int8 dht11_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)){ // Wait for DHT22 pin to go high k++; if(k > 100){ Time_out = 1; break; } delay_us(1); } delay_us(30); if(!input(dht11)) bit_clear(_data, (7 - i)); // Clear bit (7 - i) else{ bit_set(_data, (7 - i)); // Set bit (7 - i) while(input(dht11)){ // Wait for DHT22 pin to go low k++; if(k > 100){ Time_out = 1; break; } delay_us(1);} } } return _data; } void dht22_start_signal(){ output_drive(DHT22); // Configure connection pin as output output_low(DHT22); // Connection pin output low delay_ms(25); output_high(DHT22); // Connection pin output high delay_us(30); output_float(DHT22); // Configure connection pin as input } short dht22_check_response(){ delay_us(40); if(!input(DHT22)){ // Read and test if connection pin is low delay_us(80); if(input(DHT22)){ // Read and test if connection pin is high delay_us(50); return 1; } } } unsigned int8 dht22_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_state(dht22)){ // Wait for DHT22 pin to go high k++; if(k > 100){ Time_out = 1; break; } delay_us(1); } delay_us(30); if(!input_state(dht22)) bit_clear(_data, (7 - i)); // Clear bit (7 - i) else{ bit_set(_data, (7 - i)); // Set bit (7 - i) while(input_state(dht22)){ // Wait for DHT22 pin to go 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; dht11_Start_signal(); if(dht11_check_response()){ // If there is a response from dht11 sensor RH_byte1 = dht11_Read_Data(); // read RH byte1 RH_byte2 = dht11_Read_Data(); // read RH byte2 T_byte1 = dht11_Read_Data(); // read T byte1 T_byte2 = dht11_Read_Data(); // read T byte2 Checksum = dht11_Read_Data(); // read checksum if(Time_out){ // If reading takes long time lcd_gotoxy(1, 1); // Go to column 1 row 1 lcd_putc(" DHT11 Time out! "); lcd_gotoxy(1, 2); // Go to column 1 row 1 lcd_putc(" "); // Clear second row } else{ if(CheckSum == ((RH_Byte1 + RH_Byte2 + T_Byte1 + T_Byte2) & 0xFF)){ message1[13] = T_Byte1/10 + 48; message1[14] = T_Byte1%10 + 48; message1[16] = T_Byte2/10 + 48; message2[13] = RH_Byte1/10 + 48; message2[14] = RH_Byte1%10 + 48; message2[16] = RH_Byte2/10 + 48; message1[17] = 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_gotoxy(1, 1); // Go to column 1 row 1 lcd_putc("DHT11 Checksum Error"); lcd_gotoxy(1, 2); // Go to column 1 row 2 lcd_putc(" "); // Clear second row } } } else { // If dht11 sensor don't respond lcd_gotoxy(1, 1); // Go to column 1 row 1 lcd_putc(" No response "); lcd_gotoxy(1, 2); // Go to column 1 row 2 lcd_putc(" from DHT11 sensor "); } Time_out = 0; dht22_Start_signal(); if(dht22_check_response()){ // If there is a response from sensor RH_byte1 = dht22_Read_Data(); // read RH byte1 RH_byte2 = dht22_Read_Data(); // read RH byte2 T_byte1 = dht22_Read_Data(); // read T byte1 T_byte2 = dht22_Read_Data(); // read T byte2 Checksum = dht22_Read_Data(); // read checksum if(Time_out){ // If reading takes long time lcd_gotoxy(21, 1); // Go to column 1 row 1 lcd_putc(" DHT22 Time out! "); lcd_gotoxy(21, 2); // Go to column 1 row 4 lcd_putc(" "); // Clear fourth row } 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){ message3[12] = '-'; Temp = Temp & 0X7FFF; } else message3[12] = ' '; message3[13] = (Temp / 100) % 10 + 48; message3[14] = (Temp / 10) % 10 + 48; message3[16] = Temp % 10 + 48; message4[13] = (RH / 100) % 10 + 48; message4[14] = (RH / 10) % 10 + 48; message4[16] = RH % 10 + 48; message3[17] = 223; // Degree symbol lcd_gotoxy(21, 1); // Go to column 1 row 3 printf(lcd_putc, message3); // Display message3 lcd_gotoxy(21, 2); // Go to column 1 row 4 printf(lcd_putc, message4); // Display message4 } else{ lcd_gotoxy(21, 1); // Go to column 1 row 3 lcd_putc("DHT22 Checksum Error"); lcd_gotoxy(21, 2); // Go to column 1 row 4 lcd_putc(" "); // Clear fourth row } } } else { // If dht22 sensor don't respond lcd_gotoxy(21, 1); // Go to column 1 row 3 lcd_putc(" No response "); lcd_gotoxy(21, 2); // Go to column 1 row 4 lcd_putc(" from DHT22 sensor "); } delay_ms(1000); } } // End of program
DHT11 VS DHT22 Video:
The following video shows the comparison between the two sensors results.