Dht11.cpp

00001 #include "Dht11.h"
00002 
00003 Dht11::Dht11(PinName const &p) : _pin(p) {
00004     // Set creation time so we can make 
00005     // sure we pause at least 1 second for 
00006     // startup.
00007     _timer.start();
00008     
00009     _temperature = 0;
00010     _humidity = 0;
00011 }
00012 
00013 int Dht11::read()
00014 {
00015     // BUFFER TO RECEIVE
00016     uint8_t bits[5];
00017     uint8_t cnt = 7;
00018     uint8_t idx = 0;
00019 
00020     // EMPTY BUFFER
00021     for (int i=0; i< 5; i++) bits[i] = 0;
00022     
00023     // Verify sensor settled after boot
00024     while(_timer.read_ms() < 1500) {}
00025     _timer.stop();
00026 
00027     // Notify it we are ready to read
00028     _pin.output();
00029     _pin = 0;
00030     wait_ms(18);
00031     _pin = 1;
00032     wait_us(40);
00033     _pin.input();
00034 
00035     // ACKNOWLEDGE or TIMEOUT
00036     unsigned int loopCnt = 10000;
00037     while(_pin == 0)
00038         if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
00039 
00040     loopCnt = 10000;
00041     while(_pin == 1)
00042         if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
00043 
00044     // READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
00045     for (int i=0; i<40; i++)
00046     {
00047         loopCnt = 10000;
00048         while(_pin == 0)
00049             if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
00050 
00051         //unsigned long t = micros();
00052         Timer t;
00053         t. start();
00054 
00055         loopCnt = 10000;
00056         while(_pin == 1)
00057             if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT;
00058 
00059         if (t.read_us() > 40) bits[idx] |= (1 << cnt);
00060         if (cnt == 0)   // next byte?
00061         {
00062             cnt = 7;    // restart at MSB
00063             idx++;      // next byte!
00064         }
00065         else cnt--;
00066     }
00067 
00068     // WRITE TO RIGHT VARS
00069     // as bits[1] and bits[3] are allways zero they are omitted in formulas.
00070     _humidity    = bits[0]; 
00071     _temperature = bits[2]; 
00072 
00073     uint8_t sum = bits[0] + bits[2];  
00074 
00075     if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;
00076     return DHTLIB_OK;
00077 }
00078 
00079 float Dht11::getFahrenheit() {
00080     return((_temperature * 1.8) + 32);
00081 }
00082 
00083 int Dht11::getCelsius() {
00084     return(_temperature);
00085 }
00086 
00087 int Dht11::getHumidity() {
00088     return(_humidity);
00089 }