DHT.cpp

00001 /*
00002  *  DHT Library for  Digital-output Humidity and Temperature sensors
00003  *
00004  *  Works with DHT11, DHT22
00005  *             SEN11301P,  Grove - Temperature&Humidity Sensor     (Seeed Studio)
00006  *             SEN51035P,  Grove - Temperature&Humidity Sensor Pro (Seeed Studio)
00007  *             AM2302   ,  temperature-humidity sensor
00008  *             HM2303   ,  Digital-output humidity and temperature sensor
00009  *
00010  *  Copyright (C) Wim De Roeve
00011  *                based on DHT22 sensor library by HO WING KIT
00012  *                Arduino DHT11 library
00013  *
00014  * Permission is hereby granted, free of charge, to any person obtaining a copy
00015  * of this software and associated documnetation files (the "Software"), to deal
00016  * in the Software without restriction, including without limitation the rights
00017  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00018  * copies of the Software, and to permit persons to  whom the Software is
00019  * furished to do so, subject to the following conditions:
00020  *
00021  * The above copyright notice and this permission notice shall be included in
00022  * all copies or substantial portions of the Software.
00023  *
00024  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00025  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00026  * FITNESS OR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00027  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00028  * LIABILITY WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00029  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
00030  * THE SOFTWARE.
00031  */
00032 
00033 #include "DHT.h"
00034 
00035 #define DHT_DATA_BIT_COUNT 41
00036 
00037 DHT::DHT(PinName pin,int DHTtype)
00038 {
00039     _pin = pin;
00040     _DHTtype = DHTtype;
00041     _firsttime=true;
00042 }
00043 
00044 DHT::~DHT()
00045 {
00046 }
00047 
00048 int DHT::readData()
00049 {
00050     int i, j, retryCount,b;
00051     unsigned int bitTimes[DHT_DATA_BIT_COUNT];
00052 
00053     eError err = ERROR_NONE;
00054     time_t currentTime = time(NULL);
00055 
00056     DigitalInOut DHT_io(_pin);
00057 
00058     for (i = 0; i < DHT_DATA_BIT_COUNT; i++) {
00059         bitTimes[i] = 0;
00060     }
00061 
00062     if (!_firsttime) {
00063         if (int(currentTime - _lastReadTime) < 2) {
00064             err = ERROR_NO_PATIENCE;
00065             return err;
00066         }
00067     } else {
00068         _firsttime=false;
00069         _lastReadTime=currentTime;
00070     }
00071     retryCount = 0;
00072 
00073     do {
00074         if (retryCount > 125) {
00075             err = BUS_BUSY;
00076             return err;
00077         }
00078         retryCount ++;
00079         wait_us(2);
00080     } while ((DHT_io==0));
00081 
00082 
00083     DHT_io.output();
00084     DHT_io = 0;
00085     wait_ms(18);
00086     DHT_io = 1;
00087     wait_us(40);
00088     DHT_io.input();
00089 
00090     retryCount = 0;
00091     do {
00092         if (retryCount > 40)  {
00093             err = ERROR_NOT_PRESENT;
00094             return err;
00095         }
00096         retryCount++;
00097         wait_us(1);
00098     } while ((DHT_io==1));
00099 
00100     if (err != ERROR_NONE) {
00101         return err;
00102     }
00103 
00104     wait_us(80);
00105 
00106     for (i = 0; i < 5; i++) {
00107         for (j = 0; j < 8; j++) {
00108 
00109             retryCount = 0;
00110             do {
00111                 if (retryCount > 75)  {
00112                     err = ERROR_DATA_TIMEOUT;
00113                     return err;
00114                 }
00115                 retryCount++;
00116                 wait_us(1);
00117             } while (DHT_io == 0);
00118             wait_us(40);
00119             bitTimes[i*8+j]=DHT_io;
00120 
00121             int count = 0;
00122             while (DHT_io == 1 && count < 100) {
00123                 wait_us(1);
00124                 count++;
00125             }
00126         }
00127     }
00128     DHT_io.output();
00129     DHT_io = 1;
00130     for (i = 0; i < 5; i++) {
00131         b=0;
00132         for (j=0; j<8; j++) {
00133             if (bitTimes[i*8+j+1] > 0) {
00134                 b |= ( 1 << (7-j));
00135             }
00136         }
00137         DHT_data[i]=b;
00138     }
00139 
00140     if (DHT_data[4] == ((DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3]) & 0xFF)) {
00141         _lastReadTime = currentTime;
00142         _lastTemperature=CalcTemperature();
00143         _lastHumidity=CalcHumidity();
00144 
00145     } else {
00146         err = ERROR_CHECKSUM;
00147     }
00148 
00149     return err;
00150 
00151 }
00152 
00153 float DHT::CalcTemperature()
00154 {
00155     int v;
00156 
00157     switch (_DHTtype) {
00158         case DHT11:
00159             v = DHT_data[2];
00160             return float(v);
00161         case DHT22:
00162             v = DHT_data[2] & 0x7F;
00163             v *= 256;
00164             v += DHT_data[3];
00165             v /= 10;
00166             if (DHT_data[2] & 0x80)
00167                 v *= -1;
00168             return float(v);
00169     }
00170     return 0;
00171 }
00172 
00173 float DHT::ReadHumidity()
00174 {
00175     return _lastHumidity;
00176 }
00177 
00178 float DHT::ConvertCelciustoFarenheit(float celsius)
00179 {
00180     return celsius * 9 / 5 + 32;
00181 }
00182 
00183 float DHT::ConvertCelciustoKelvin(float celsius)
00184 {
00185     return celsius + (float)273.15;
00186 }
00187 
00188 // dewPoint function NOAA
00189 // reference: http://wahiduddin.net/calc/density_algorithms.htm
00190 float DHT::CalcdewPoint(float celsius, float humidity)
00191 {
00192     float A0= (float)373.15/((float)273.15 + celsius);
00193     float SUM = (float)-7.90298 * (A0-1);
00194     SUM += (float)5.02808 * log10(A0);
00195     SUM += -1.3816e-7 * (pow(10, ((float)11.344*(1-1/A0)))-1) ;
00196     SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
00197     SUM += log10(1013.246);
00198     float VP = pow(10, SUM-3) * humidity;
00199     float T = log(VP/(float)0.61078);   // temp var
00200     return ((float)241.88 * T) / ((float)17.558-T);
00201 }
00202 
00203 // delta max = 0.6544 wrt dewPoint()
00204 // 5x faster than dewPoint()
00205 // reference: http://en.wikipedia.org/wiki/Dew_point
00206 float DHT::CalcdewPointFast(float celsius, float humidity)
00207 {
00208     float a = 17.271;
00209     float b = 237.7;
00210     float temp = (a * celsius) / (b + celsius) + log(humidity/100);
00211     float Td = (b * temp) / (a - temp);
00212     return Td;
00213 }
00214 
00215 float DHT::ReadTemperature(eScale Scale)
00216 {
00217     if (Scale == FARENHEIT)
00218         return ConvertCelciustoFarenheit(_lastTemperature);
00219     else if (Scale == KELVIN)
00220         return ConvertCelciustoKelvin(_lastTemperature);
00221     else
00222         return _lastTemperature;
00223 }
00224 
00225 float DHT::CalcHumidity()
00226 {
00227     int v;
00228 
00229     switch (_DHTtype) {
00230         case DHT11:
00231             v = DHT_data[0];
00232             return float(v);
00233         case DHT22:
00234             v = DHT_data[0];
00235             v *= 256;
00236             v += DHT_data[1];
00237             v /= 10;
00238             return float(v);
00239     }
00240     return 0;
00241 }