Giorgos Tsapparellas / DHT11

DHT11 used for Temperature & Humidity sensor.

Dependents:   LoRaWAN_mbed_lmic_agriculture_app

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
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