DHT11.h

00001 #ifndef DHT11_H
00002 #define DHT11_H
00003 
00004 //Class to manage DHT11 sensor
00005 class DHT11{
00006   
00007     public:
00008         /* Takes the data pin of the sensor in parameter */
00009         DHT11(PinName pin):dataPin(pin)
00010         {
00011             iBit = 0;
00012             data = 0;
00013         }  
00014         
00015         /*  Request and receive new data from sensor
00016             Returns : 
00017                 1 : OK
00018                 -1 : Checksum Error
00019         */
00020         int readData(void){
00021             this->data = 0;
00022             this->dataPin.output(); 
00023             // Request a measurement (low during t > 18ms)
00024             this->dataPin = 0;
00025             wait_ms(20);
00026             this->dataPin = 1;
00027             
00028             //Wait for the sensor to take control and set low level /!\ Important
00029             wait_us(20);
00030             
00031             this->dataPin.input();
00032             
00033         //TODO Check if timing is correct (low : 80µs ; high 80µs)
00034             // Wait until end of 80µs low
00035             while(!this->dataPin.read());
00036             // Wait until end of 80 µs high
00037             while(this->dataPin.read());
00038             
00039             // Sensor reply 40bits 
00040             for(iBit=0; iBit<40; iBit++) {
00041                 this->data = this->data << 1; // Shift for new number
00042                 this->timer.stop(); 
00043                 this->timer.reset(); 
00044                 
00045                 // Wait for low level to end
00046                 while(!this->dataPin.read());       
00047                 this->timer.start();     
00048                 // Count time while high level     
00049                 while(this->dataPin.read());
00050                 
00051                 if(this->timer.read_us() > 50) 
00052                 {
00053                     //This bit is '1'
00054                     this->data++;
00055                 }
00056             }
00057             
00058             wait_ms(250);
00059             
00060             //Checking checksum
00061             if((this->data & 0x00000000000000ff) != ((this->data & 0x000000ff00000000) >> 32) + 
00062                                                     ((this->data & 0x00000000ff000000) >> 24) + 
00063                                                     ((this->data & 0x0000000000ff0000) >> 16) + 
00064                                                     ((this->data & 0x000000000000ff00) >> 8))
00065             {
00066                 return -1;        
00067             }
00068             
00069             return 1;
00070         }
00071         
00072         int getTemperature(void){
00073             return (int)((this->data & 0x0000000000ff0000) >> 16);
00074         }
00075         
00076         int getHumidity(void){
00077             return (int)((this->data & 0x000000ff00000000) >> 32);
00078         }
00079         
00080     
00081     private:
00082         DigitalInOut dataPin;//Communication with the sensor
00083         Timer timer; //initialize timer
00084         uint64_t data; // 64 bit variable for temporary data
00085         int iBit;
00086 };
00087 
00088 
00089 #endif