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 40
00036 
00037 DHT::DHT(PinName pin, eType DHTtype)
00038 {
00039     _pin = pin;
00040     _DHTtype = DHTtype;
00041     _firsttime = true;
00042 }
00043 
00044 DHT::~DHT()
00045 {
00046     
00047 }
00048 
00049 eError DHT::stall(DigitalInOut &io, int const level, int const max_time)
00050 {
00051     int cnt = 0;
00052     while (level == io) {
00053         if (cnt > max_time) {
00054             return ERROR_NO_PATIENCE;
00055         }
00056         cnt++;
00057         wait_us(1);
00058     }
00059     return ERROR_NONE;
00060 }
00061 
00062 eError DHT::readData()
00063 {
00064     uint8_t i = 0, j = 0, b = 0, data_valid = 0;
00065     uint32_t bit_value[DHT_DATA_BIT_COUNT] = {0};
00066 
00067     eError err = ERROR_NONE;
00068     time_t currentTime = time(NULL);
00069 
00070     DigitalInOut DHT_io(_pin);
00071 
00072     // IO must be in hi state to start
00073     if (ERROR_NONE != stall(DHT_io, 0, 250)) {
00074         return BUS_BUSY;
00075     }
00076 
00077     // start the transfer
00078     DHT_io.output();
00079     DHT_io = 0;
00080     // only 500uS for DHT22 but 18ms for DHT11
00081     (_DHTtype == 11) ? wait_ms(18) : wait(1);
00082     DHT_io = 1;
00083     wait_us(30);
00084     DHT_io.input();
00085     // wait till the sensor grabs the bus
00086     if (ERROR_NONE != stall(DHT_io, 1, 40)) {
00087         return ERROR_NOT_PRESENT;
00088     }
00089     // sensor should signal low 80us and then hi 80us
00090     if (ERROR_NONE != stall(DHT_io, 0, 100)) {
00091         return ERROR_SYNC_TIMEOUT;
00092     }
00093     if (ERROR_NONE != stall(DHT_io, 1, 100)) {
00094         return ERROR_NO_PATIENCE;
00095     }
00096     // capture the data
00097     for (i = 0; i < 5; i++) {
00098         for (j = 0; j < 8; j++) {
00099             if (ERROR_NONE != stall(DHT_io, 0, 75)) {
00100                 return ERROR_DATA_TIMEOUT;
00101             }
00102             // logic 0 is 28us max, 1 is 70us
00103             wait_us(40);
00104             bit_value[i*8+j] = DHT_io;
00105             if (ERROR_NONE != stall(DHT_io, 1, 50)) {
00106                 return ERROR_DATA_TIMEOUT;
00107             }
00108         }
00109     }
00110     // store the data
00111     for (i = 0; i < 5; i++) {
00112         b=0;
00113         for (j=0; j<8; j++) {
00114             if (bit_value[i*8+j] == 1) {
00115                 b |= (1 << (7-j));
00116             }
00117         }
00118         DHT_data[i]=b;
00119     }
00120 
00121     // uncomment to see the checksum error if it exists
00122     //printf(" 0x%02x + 0x%02x + 0x%02x + 0x%02x = 0x%02x \n", DHT_data[0], DHT_data[1], DHT_data[2], DHT_data[3], DHT_data[4]);
00123     data_valid = DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3];
00124     if (DHT_data[4] == data_valid) {
00125         _lastReadTime = currentTime;
00126         _lastTemperature = CalcTemperature();
00127         _lastHumidity = CalcHumidity();
00128 
00129     } else {
00130         err = ERROR_CHECKSUM;
00131     }
00132 
00133     return err;
00134 
00135 }
00136 
00137 float DHT::CalcTemperature()
00138 {
00139     int v;
00140 
00141     switch (_DHTtype) {
00142         case DHT11:
00143             v = DHT_data[2];
00144             return float(v);
00145         case DHT22:
00146             v = DHT_data[2] & 0x7F;
00147             v *= 256;
00148             v += DHT_data[3];
00149             v /= 10;
00150             if (DHT_data[2] & 0x80)
00151                 v *= -1;
00152             return float(v);
00153     }
00154     return 0;
00155 }
00156 
00157 float DHT::ReadHumidity()
00158 {
00159     return _lastHumidity;
00160 }
00161 
00162 float DHT::ConvertCelciustoFarenheit(float const celsius)
00163 {
00164     return celsius * 9 / 5 + 32;
00165 }
00166 
00167 float DHT::ConvertCelciustoKelvin(float const celsius)
00168 {
00169     return celsius + 273.15;
00170 }
00171 
00172 // dewPoint function NOAA
00173 // reference: http://wahiduddin.net/calc/density_algorithms.htm
00174 float DHT::CalcdewPoint(float const celsius, float const humidity)
00175 {
00176     float A0= 373.15/(273.15 + celsius);
00177     float SUM = -7.90298 * (A0-1);
00178     SUM += 5.02808 * log10(A0);
00179     SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
00180     SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
00181     SUM += log10(1013.246);
00182     float VP = pow(10, SUM-3) * humidity;
00183     float T = log(VP/0.61078);   // temp var
00184     return (241.88 * T) / (17.558-T);
00185 }
00186 
00187 // delta max = 0.6544 wrt dewPoint()
00188 // 5x faster than dewPoint()
00189 // reference: http://en.wikipedia.org/wiki/Dew_point
00190 float DHT::CalcdewPointFast(float const celsius, float const humidity)
00191 {
00192     float a = 17.271;
00193     float b = 237.7;
00194     float temp = (a * celsius) / (b + celsius) + log(humidity/100);
00195     float Td = (b * temp) / (a - temp);
00196     return Td;
00197 }
00198 
00199 float DHT::ReadTemperature(eScale Scale)
00200 {
00201     if (Scale == FARENHEIT)
00202         return ConvertCelciustoFarenheit(_lastTemperature);
00203     else if (Scale == KELVIN)
00204         return ConvertCelciustoKelvin(_lastTemperature);
00205     else
00206         return _lastTemperature;
00207 }
00208 
00209 float DHT::CalcHumidity()
00210 {
00211     int v;
00212 
00213     switch (_DHTtype) {
00214         case DHT11:
00215             v = DHT_data[0];
00216             return float(v);
00217         case DHT22:
00218             v = DHT_data[0];
00219             v *= 256;
00220             v += DHT_data[1];
00221             v /= 10;
00222             return float(v);
00223     }
00224     return 0;
00225 }
00226 
00227