Akash Gaikwad / DHT

Important changes to repositories hosted on mbed.com

Mbed hosted mercurial repositories are deprecated and are due to be permanently deleted in July 2026.

To keep a copy of this software download the repository Zip archive or clone locally using Mercurial.

It is also possible to export all your personal repositories from the account settings page.

Fork of DHT by Components

DHT.cpp@2:df22ddf10d75, 2014-08-15 (annotated)

Committer:
sam_grove
Date:
Fri Aug 15 20:55:43 2014 +0000
Revision:
2:df22ddf10d75
Parent:
1:25c96950b6ed
Child:
3:6937e130feca
Child:
4:171c12efa794
Update reading sensor to eliminate the checksum error (error 6). Many other changes for good coding practices

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Wimpie 0:9b5b3200688f 1 /*
Wimpie 0:9b5b3200688f 2 * DHT Library for Digital-output Humidity and Temperature sensors
Wimpie 0:9b5b3200688f 3 *
Wimpie 0:9b5b3200688f 4 * Works with DHT11, DHT22
Wimpie 0:9b5b3200688f 5 * SEN11301P, Grove - Temperature&Humidity Sensor (Seeed Studio)
Wimpie 0:9b5b3200688f 6 * SEN51035P, Grove - Temperature&Humidity Sensor Pro (Seeed Studio)
Wimpie 0:9b5b3200688f 7 * AM2302 , temperature-humidity sensor
Wimpie 0:9b5b3200688f 8 * HM2303 , Digital-output humidity and temperature sensor
Wimpie 0:9b5b3200688f 9 *
Wimpie 0:9b5b3200688f 10 * Copyright (C) Wim De Roeve
Wimpie 0:9b5b3200688f 11 * based on DHT22 sensor library by HO WING KIT
sam_grove 2:df22ddf10d75 12 * Arduino DHT11 library
Wimpie 0:9b5b3200688f 13 *
Wimpie 0:9b5b3200688f 14 * Permission is hereby granted, free of charge, to any person obtaining a copy
Wimpie 0:9b5b3200688f 15 * of this software and associated documnetation files (the "Software"), to deal
Wimpie 0:9b5b3200688f 16 * in the Software without restriction, including without limitation the rights
Wimpie 0:9b5b3200688f 17 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
Wimpie 0:9b5b3200688f 18 * copies of the Software, and to permit persons to whom the Software is
Wimpie 0:9b5b3200688f 19 * furished to do so, subject to the following conditions:
Wimpie 0:9b5b3200688f 20 *
Wimpie 0:9b5b3200688f 21 * The above copyright notice and this permission notice shall be included in
Wimpie 0:9b5b3200688f 22 * all copies or substantial portions of the Software.
Wimpie 0:9b5b3200688f 23 *
Wimpie 0:9b5b3200688f 24 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
Wimpie 0:9b5b3200688f 25 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
Wimpie 0:9b5b3200688f 26 * FITNESS OR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
Wimpie 0:9b5b3200688f 27 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
Wimpie 0:9b5b3200688f 28 * LIABILITY WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
Wimpie 0:9b5b3200688f 29 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
Wimpie 0:9b5b3200688f 30 * THE SOFTWARE.
Wimpie 0:9b5b3200688f 31 */
Wimpie 0:9b5b3200688f 32
Wimpie 0:9b5b3200688f 33 #include "DHT.h"
Wimpie 0:9b5b3200688f 34
sam_grove 2:df22ddf10d75 35 #define DHT_DATA_BIT_COUNT 40
Wimpie 0:9b5b3200688f 36
sam_grove 2:df22ddf10d75 37 DHT::DHT(PinName pin, eType DHTtype)
sam_grove 2:df22ddf10d75 38 {
Wimpie 0:9b5b3200688f 39 _pin = pin;
Wimpie 0:9b5b3200688f 40 _DHTtype = DHTtype;
sam_grove 2:df22ddf10d75 41 _firsttime = true;
sam_grove 2:df22ddf10d75 42 }
sam_grove 2:df22ddf10d75 43
sam_grove 2:df22ddf10d75 44 DHT::~DHT()
sam_grove 2:df22ddf10d75 45 {
sam_grove 2:df22ddf10d75 46
Wimpie 0:9b5b3200688f 47 }
Wimpie 0:9b5b3200688f 48
sam_grove 2:df22ddf10d75 49 eError DHT::stall(DigitalInOut &io, int const level, int const max_time)
sam_grove 2:df22ddf10d75 50 {
sam_grove 2:df22ddf10d75 51 int cnt = 0;
sam_grove 2:df22ddf10d75 52 while (level == io) {
sam_grove 2:df22ddf10d75 53 if (cnt > max_time) {
sam_grove 2:df22ddf10d75 54 return ERROR_NO_PATIENCE;
sam_grove 2:df22ddf10d75 55 }
sam_grove 2:df22ddf10d75 56 cnt++;
sam_grove 2:df22ddf10d75 57 wait_us(1);
sam_grove 2:df22ddf10d75 58 }
sam_grove 2:df22ddf10d75 59 return ERROR_NONE;
Wimpie 0:9b5b3200688f 60 }
Wimpie 0:9b5b3200688f 61
sam_grove 2:df22ddf10d75 62 eError DHT::readData()
sam_grove 2:df22ddf10d75 63 {
sam_grove 2:df22ddf10d75 64 uint8_t i = 0, j = 0, b = 0, data_valid = 0;
sam_grove 2:df22ddf10d75 65 uint32_t bit_value[DHT_DATA_BIT_COUNT] = {0};
Wimpie 0:9b5b3200688f 66
Wimpie 0:9b5b3200688f 67 eError err = ERROR_NONE;
Wimpie 0:9b5b3200688f 68 time_t currentTime = time(NULL);
Wimpie 0:9b5b3200688f 69
Wimpie 0:9b5b3200688f 70 DigitalInOut DHT_io(_pin);
Wimpie 0:9b5b3200688f 71
sam_grove 2:df22ddf10d75 72 // IO must be in hi state to start
sam_grove 2:df22ddf10d75 73 if (ERROR_NONE != stall(DHT_io, 0, 250)) {
sam_grove 2:df22ddf10d75 74 return BUS_BUSY;
Wimpie 0:9b5b3200688f 75 }
Wimpie 0:9b5b3200688f 76
sam_grove 2:df22ddf10d75 77 // start the transfer
Wimpie 0:9b5b3200688f 78 DHT_io.output();
Wimpie 0:9b5b3200688f 79 DHT_io = 0;
sam_grove 2:df22ddf10d75 80 // only 500uS for DHT22 but 18ms for DHT11
sam_grove 2:df22ddf10d75 81 (_DHTtype == 11) ? wait_ms(18) : wait(1);
Wimpie 0:9b5b3200688f 82 DHT_io = 1;
sam_grove 2:df22ddf10d75 83 wait_us(30);
Wimpie 0:9b5b3200688f 84 DHT_io.input();
sam_grove 2:df22ddf10d75 85 // wait till the sensor grabs the bus
sam_grove 2:df22ddf10d75 86 if (ERROR_NONE != stall(DHT_io, 1, 40)) {
sam_grove 2:df22ddf10d75 87 return ERROR_NOT_PRESENT;
Wimpie 0:9b5b3200688f 88 }
sam_grove 2:df22ddf10d75 89 // sensor should signal low 80us and then hi 80us
sam_grove 2:df22ddf10d75 90 if (ERROR_NONE != stall(DHT_io, 0, 100)) {
sam_grove 2:df22ddf10d75 91 return ERROR_SYNC_TIMEOUT;
sam_grove 2:df22ddf10d75 92 }
sam_grove 2:df22ddf10d75 93 if (ERROR_NONE != stall(DHT_io, 1, 100)) {
sam_grove 2:df22ddf10d75 94 return ERROR_NO_PATIENCE;
sam_grove 2:df22ddf10d75 95 }
sam_grove 2:df22ddf10d75 96 // capture the data
Wimpie 0:9b5b3200688f 97 for (i = 0; i < 5; i++) {
Wimpie 0:9b5b3200688f 98 for (j = 0; j < 8; j++) {
sam_grove 2:df22ddf10d75 99 if (ERROR_NONE != stall(DHT_io, 0, 75)) {
sam_grove 2:df22ddf10d75 100 return ERROR_DATA_TIMEOUT;
sam_grove 2:df22ddf10d75 101 }
sam_grove 2:df22ddf10d75 102 // logic 0 is 28us max, 1 is 70us
Wimpie 0:9b5b3200688f 103 wait_us(40);
sam_grove 2:df22ddf10d75 104 bit_value[i*8+j] = DHT_io;
sam_grove 2:df22ddf10d75 105 if (ERROR_NONE != stall(DHT_io, 1, 50)) {
sam_grove 2:df22ddf10d75 106 return ERROR_DATA_TIMEOUT;
Wimpie 0:9b5b3200688f 107 }
Wimpie 0:9b5b3200688f 108 }
Wimpie 0:9b5b3200688f 109 }
sam_grove 2:df22ddf10d75 110 // store the data
Wimpie 0:9b5b3200688f 111 for (i = 0; i < 5; i++) {
Wimpie 0:9b5b3200688f 112 b=0;
Wimpie 0:9b5b3200688f 113 for (j=0; j<8; j++) {
sam_grove 2:df22ddf10d75 114 if (bit_value[i*8+j] == 1) {
sam_grove 2:df22ddf10d75 115 b |= (1 << (7-j));
Wimpie 0:9b5b3200688f 116 }
Wimpie 0:9b5b3200688f 117 }
Wimpie 0:9b5b3200688f 118 DHT_data[i]=b;
Wimpie 0:9b5b3200688f 119 }
Wimpie 0:9b5b3200688f 120
sam_grove 2:df22ddf10d75 121 // uncomment to see the checksum error if it exists
sam_grove 2:df22ddf10d75 122 //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]);
sam_grove 2:df22ddf10d75 123 data_valid = DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3];
sam_grove 2:df22ddf10d75 124 if (DHT_data[4] == data_valid) {
Wimpie 0:9b5b3200688f 125 _lastReadTime = currentTime;
sam_grove 2:df22ddf10d75 126 _lastTemperature = CalcTemperature();
sam_grove 2:df22ddf10d75 127 _lastHumidity = CalcHumidity();
Wimpie 0:9b5b3200688f 128
Wimpie 0:9b5b3200688f 129 } else {
Wimpie 0:9b5b3200688f 130 err = ERROR_CHECKSUM;
Wimpie 0:9b5b3200688f 131 }
Wimpie 0:9b5b3200688f 132
Wimpie 0:9b5b3200688f 133 return err;
Wimpie 0:9b5b3200688f 134
Wimpie 0:9b5b3200688f 135 }
Wimpie 0:9b5b3200688f 136
sam_grove 2:df22ddf10d75 137 float DHT::CalcTemperature()
sam_grove 2:df22ddf10d75 138 {
Wimpie 0:9b5b3200688f 139 int v;
Wimpie 0:9b5b3200688f 140
Wimpie 0:9b5b3200688f 141 switch (_DHTtype) {
Wimpie 0:9b5b3200688f 142 case DHT11:
Wimpie 0:9b5b3200688f 143 v = DHT_data[2];
Wimpie 0:9b5b3200688f 144 return float(v);
Wimpie 0:9b5b3200688f 145 case DHT22:
Wimpie 0:9b5b3200688f 146 v = DHT_data[2] & 0x7F;
Wimpie 0:9b5b3200688f 147 v *= 256;
Wimpie 0:9b5b3200688f 148 v += DHT_data[3];
Wimpie 0:9b5b3200688f 149 v /= 10;
Wimpie 0:9b5b3200688f 150 if (DHT_data[2] & 0x80)
Wimpie 0:9b5b3200688f 151 v *= -1;
Wimpie 0:9b5b3200688f 152 return float(v);
Wimpie 0:9b5b3200688f 153 }
Wimpie 0:9b5b3200688f 154 return 0;
Wimpie 0:9b5b3200688f 155 }
Wimpie 0:9b5b3200688f 156
sam_grove 2:df22ddf10d75 157 float DHT::ReadHumidity()
sam_grove 2:df22ddf10d75 158 {
Wimpie 0:9b5b3200688f 159 return _lastHumidity;
Wimpie 0:9b5b3200688f 160 }
Wimpie 0:9b5b3200688f 161
sam_grove 2:df22ddf10d75 162 float DHT::ConvertCelciustoFarenheit(float const celsius)
sam_grove 2:df22ddf10d75 163 {
Wimpie 0:9b5b3200688f 164 return celsius * 9 / 5 + 32;
Wimpie 0:9b5b3200688f 165 }
Wimpie 0:9b5b3200688f 166
sam_grove 2:df22ddf10d75 167 float DHT::ConvertCelciustoKelvin(float const celsius)
sam_grove 2:df22ddf10d75 168 {
Wimpie 0:9b5b3200688f 169 return celsius + 273.15;
Wimpie 0:9b5b3200688f 170 }
Wimpie 0:9b5b3200688f 171
Wimpie 0:9b5b3200688f 172 // dewPoint function NOAA
Wimpie 0:9b5b3200688f 173 // reference: http://wahiduddin.net/calc/density_algorithms.htm
sam_grove 2:df22ddf10d75 174 float DHT::CalcdewPoint(float const celsius, float const humidity)
sam_grove 2:df22ddf10d75 175 {
Wimpie 0:9b5b3200688f 176 float A0= 373.15/(273.15 + celsius);
Wimpie 0:9b5b3200688f 177 float SUM = -7.90298 * (A0-1);
Wimpie 0:9b5b3200688f 178 SUM += 5.02808 * log10(A0);
Wimpie 0:9b5b3200688f 179 SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
Wimpie 0:9b5b3200688f 180 SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
Wimpie 0:9b5b3200688f 181 SUM += log10(1013.246);
Wimpie 0:9b5b3200688f 182 float VP = pow(10, SUM-3) * humidity;
Wimpie 0:9b5b3200688f 183 float T = log(VP/0.61078); // temp var
Wimpie 0:9b5b3200688f 184 return (241.88 * T) / (17.558-T);
Wimpie 0:9b5b3200688f 185 }
Wimpie 0:9b5b3200688f 186
Wimpie 0:9b5b3200688f 187 // delta max = 0.6544 wrt dewPoint()
Wimpie 0:9b5b3200688f 188 // 5x faster than dewPoint()
Wimpie 0:9b5b3200688f 189 // reference: http://en.wikipedia.org/wiki/Dew_point
sam_grove 2:df22ddf10d75 190 float DHT::CalcdewPointFast(float const celsius, float const humidity)
Wimpie 0:9b5b3200688f 191 {
sam_grove 2:df22ddf10d75 192 float a = 17.271;
sam_grove 2:df22ddf10d75 193 float b = 237.7;
sam_grove 2:df22ddf10d75 194 float temp = (a * celsius) / (b + celsius) + log(humidity/100);
sam_grove 2:df22ddf10d75 195 float Td = (b * temp) / (a - temp);
sam_grove 2:df22ddf10d75 196 return Td;
Wimpie 0:9b5b3200688f 197 }
Wimpie 0:9b5b3200688f 198
sam_grove 2:df22ddf10d75 199 float DHT::ReadTemperature(eScale Scale)
sam_grove 2:df22ddf10d75 200 {
Wimpie 0:9b5b3200688f 201 if (Scale == FARENHEIT)
Wimpie 0:9b5b3200688f 202 return ConvertCelciustoFarenheit(_lastTemperature);
Wimpie 0:9b5b3200688f 203 else if (Scale == KELVIN)
Wimpie 0:9b5b3200688f 204 return ConvertCelciustoKelvin(_lastTemperature);
Wimpie 0:9b5b3200688f 205 else
Wimpie 0:9b5b3200688f 206 return _lastTemperature;
Wimpie 0:9b5b3200688f 207 }
Wimpie 0:9b5b3200688f 208
sam_grove 2:df22ddf10d75 209 float DHT::CalcHumidity()
sam_grove 2:df22ddf10d75 210 {
Wimpie 0:9b5b3200688f 211 int v;
Wimpie 0:9b5b3200688f 212
Wimpie 0:9b5b3200688f 213 switch (_DHTtype) {
Wimpie 0:9b5b3200688f 214 case DHT11:
Wimpie 0:9b5b3200688f 215 v = DHT_data[0];
Wimpie 0:9b5b3200688f 216 return float(v);
Wimpie 0:9b5b3200688f 217 case DHT22:
Wimpie 0:9b5b3200688f 218 v = DHT_data[0];
Wimpie 0:9b5b3200688f 219 v *= 256;
Wimpie 0:9b5b3200688f 220 v += DHT_data[1];
Wimpie 0:9b5b3200688f 221 v /= 10;
Wimpie 0:9b5b3200688f 222 return float(v);
Wimpie 0:9b5b3200688f 223 }
Wimpie 0:9b5b3200688f 224 return 0;
Wimpie 0:9b5b3200688f 225 }
Wimpie 0:9b5b3200688f 226
Wimpie 0:9b5b3200688f 227