Andy Pomfret / DHT11

Simple library for the DHT11 temperature and humidity sensor. Forked from an existing Mbed DHT11 project.

Dependents:   UoY-DHT11-test

Simple DHT11 temperature and humidity library.

Example usage

#include "mbed.h"
#include "DHT11.h"

DHT11 dht(D8); // Change pin name here if required

main()
{
    printf("T:%d, H:%d\r\n", dht.readTemperature(), dht.readHumidity());
}

The sensor may be read as often as desired, but temperature and humidity values are cached and will only be updated if they are more than 2 seconds old. This is the underlying sensor update rate.

Please note that this project has been modified only enough to make it work for its intended purpose. Various parts of this project still need work, and the source code should not be seen as an example of best practice.

DHT11.cpp@10:f0d789f49df7, 2014-09-16 (annotated)

Committer:
s_inoue_mbed
Date:
Tue Sep 16 13:06:43 2014 +0000
Revision:
10:f0d789f49df7
Parent:
9:056d1e9b428c
Child:
11:e91c151d1798
License has been changed from Apache2 to MIT lisence.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
s_inoue_mbed 10:f0d789f49df7 1 /* Copyright (c) 2014 Shigenori Inoue, MIT License
s_inoue_mbed 10:f0d789f49df7 2 *
s_inoue_mbed 10:f0d789f49df7 3 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
s_inoue_mbed 10:f0d789f49df7 4 * and associated documentation files (the "Software"), to deal in the Software without restriction,
s_inoue_mbed 10:f0d789f49df7 5 * including without limitation the rights to use, copy, modify, merge, publish, distribute,
s_inoue_mbed 10:f0d789f49df7 6 * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
s_inoue_mbed 10:f0d789f49df7 7 * furnished to do so, subject to the following conditions:
s_inoue_mbed 10:f0d789f49df7 8 *
s_inoue_mbed 10:f0d789f49df7 9 * The above copyright notice and this permission notice shall be included in all copies or
s_inoue_mbed 10:f0d789f49df7 10 * substantial portions of the Software.
s_inoue_mbed 10:f0d789f49df7 11 *
s_inoue_mbed 10:f0d789f49df7 12 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
s_inoue_mbed 10:f0d789f49df7 13 * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
s_inoue_mbed 10:f0d789f49df7 14 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
s_inoue_mbed 10:f0d789f49df7 15 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
s_inoue_mbed 10:f0d789f49df7 16 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
s_inoue_mbed 0:4d4c5ea17d86 17 */
s_inoue_mbed 0:4d4c5ea17d86 18
s_inoue_mbed 0:4d4c5ea17d86 19 #include "DHT11.h"
s_inoue_mbed 0:4d4c5ea17d86 20
s_inoue_mbed 0:4d4c5ea17d86 21 // Constructor
s_inoue_mbed 0:4d4c5ea17d86 22 DHT11::DHT11(PinName pin) : io(pin, PIN_INPUT, OpenDrain, 1), io_irq(pin)
s_inoue_mbed 0:4d4c5ea17d86 23 {
s_inoue_mbed 0:4d4c5ea17d86 24 io_irq.rise(this, &DHT11::pos_edge);
s_inoue_mbed 0:4d4c5ea17d86 25 io_irq.fall(this, &DHT11::neg_edge);
s_inoue_mbed 0:4d4c5ea17d86 26 io_irq.disable_irq();
s_inoue_mbed 9:056d1e9b428c 27 t.start();
s_inoue_mbed 6:257e2ab66d0f 28 first_time = true;
s_inoue_mbed 0:4d4c5ea17d86 29 }
s_inoue_mbed 0:4d4c5ea17d86 30
s_inoue_mbed 0:4d4c5ea17d86 31 // Destructor
s_inoue_mbed 0:4d4c5ea17d86 32 DHT11::~DHT11(void) {}
s_inoue_mbed 0:4d4c5ea17d86 33
s_inoue_mbed 9:056d1e9b428c 34 // Constants
s_inoue_mbed 9:056d1e9b428c 35 const int DHT11::t_tol_start = 2;
s_inoue_mbed 9:056d1e9b428c 36 const int DHT11::t_tol_pulse = 10;
s_inoue_mbed 9:056d1e9b428c 37
s_inoue_mbed 6:257e2ab66d0f 38 // Reading the data bits from the DHT11
s_inoue_mbed 9:056d1e9b428c 39 int DHT11::readData(void)
s_inoue_mbed 0:4d4c5ea17d86 40 {
s_inoue_mbed 9:056d1e9b428c 41 // Checking the measurement frequency
s_inoue_mbed 9:056d1e9b428c 42 if (t.read_ms() < 2000 && first_time == false) {
s_inoue_mbed 9:056d1e9b428c 43 t.reset();
s_inoue_mbed 9:056d1e9b428c 44 return READ_TOO_OFTEN;
s_inoue_mbed 9:056d1e9b428c 45 }
s_inoue_mbed 9:056d1e9b428c 46
s_inoue_mbed 0:4d4c5ea17d86 47 // Initialize
s_inoue_mbed 6:257e2ab66d0f 48 init();
s_inoue_mbed 0:4d4c5ea17d86 49
s_inoue_mbed 0:4d4c5ea17d86 50 // Checking the data bus
s_inoue_mbed 0:4d4c5ea17d86 51 if (io == 0) {
s_inoue_mbed 9:056d1e9b428c 52 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 53 return BUS_BUSY;
s_inoue_mbed 0:4d4c5ea17d86 54 }
s_inoue_mbed 0:4d4c5ea17d86 55
s_inoue_mbed 9:056d1e9b428c 56 // Sending start signal, low signal for around 10 ms
s_inoue_mbed 0:4d4c5ea17d86 57 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 58 do {
s_inoue_mbed 0:4d4c5ea17d86 59 io = 0;
s_inoue_mbed 9:056d1e9b428c 60 } while (t.read_ms() < 20 + t_tol_start);
s_inoue_mbed 7:50f5c8efd967 61 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 62
s_inoue_mbed 0:4d4c5ea17d86 63 // Waiting for the start of the response signal
s_inoue_mbed 0:4d4c5ea17d86 64 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 65 do {
s_inoue_mbed 0:4d4c5ea17d86 66 if (t.read_us() > 100) {
s_inoue_mbed 9:056d1e9b428c 67 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 68 return NOT_PRESENT;
s_inoue_mbed 0:4d4c5ea17d86 69 }
s_inoue_mbed 0:4d4c5ea17d86 70 } while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 71
s_inoue_mbed 0:4d4c5ea17d86 72 // Wainting for the start of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 73 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 74 do {
s_inoue_mbed 0:4d4c5ea17d86 75 if (t.read_us() > 100) {
s_inoue_mbed 9:056d1e9b428c 76 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 77 return NOT_READY;
s_inoue_mbed 0:4d4c5ea17d86 78 }
s_inoue_mbed 0:4d4c5ea17d86 79 } while (io == 0);
s_inoue_mbed 0:4d4c5ea17d86 80
s_inoue_mbed 0:4d4c5ea17d86 81 // Wainting for the end of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 82 t.reset();
s_inoue_mbed 9:056d1e9b428c 83 do {
s_inoue_mbed 9:056d1e9b428c 84 if (t.read_us() > 100) {
s_inoue_mbed 9:056d1e9b428c 85 t.reset();
s_inoue_mbed 9:056d1e9b428c 86 return WATCHDOG_ERR;
s_inoue_mbed 9:056d1e9b428c 87 }
s_inoue_mbed 9:056d1e9b428c 88 } while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 89
s_inoue_mbed 0:4d4c5ea17d86 90 // Starting the pulse width sensing
s_inoue_mbed 9:056d1e9b428c 91 // by the use of interruptions
s_inoue_mbed 0:4d4c5ea17d86 92 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 93
s_inoue_mbed 0:4d4c5ea17d86 94 do {
s_inoue_mbed 0:4d4c5ea17d86 95 wait_us(100);
s_inoue_mbed 0:4d4c5ea17d86 96 if (wdt > 50) {
s_inoue_mbed 9:056d1e9b428c 97 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 98 return WATCHDOG_ERR;
s_inoue_mbed 0:4d4c5ea17d86 99 }
s_inoue_mbed 0:4d4c5ea17d86 100 wdt++;
s_inoue_mbed 0:4d4c5ea17d86 101 } while (eod == false);
s_inoue_mbed 0:4d4c5ea17d86 102
s_inoue_mbed 0:4d4c5ea17d86 103 // Calculating the check sum
s_inoue_mbed 0:4d4c5ea17d86 104 chksum = ((data & 0xff00000000) >> 32)
s_inoue_mbed 0:4d4c5ea17d86 105 + ((data & 0x00ff000000) >> 24)
s_inoue_mbed 0:4d4c5ea17d86 106 + ((data & 0x0000ff0000) >> 16)
s_inoue_mbed 0:4d4c5ea17d86 107 + ((data & 0x000000ff00) >> 8);
s_inoue_mbed 9:056d1e9b428c 108
s_inoue_mbed 0:4d4c5ea17d86 109 if (chksum != (data & 0x00000000ff)) {
s_inoue_mbed 9:056d1e9b428c 110 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 111 return CHKSUM_ERR;
s_inoue_mbed 0:4d4c5ea17d86 112 } else {
s_inoue_mbed 0:4d4c5ea17d86 113 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 114 first_time = false;
s_inoue_mbed 0:4d4c5ea17d86 115 return OK;
s_inoue_mbed 0:4d4c5ea17d86 116 }
s_inoue_mbed 0:4d4c5ea17d86 117 }
s_inoue_mbed 0:4d4c5ea17d86 118
s_inoue_mbed 0:4d4c5ea17d86 119 // Extracting humidity data from the received data
s_inoue_mbed 9:056d1e9b428c 120 int DHT11::readHumidity(void)
s_inoue_mbed 0:4d4c5ea17d86 121 {
s_inoue_mbed 9:056d1e9b428c 122 return (data & 0xff00000000) >> 32;
s_inoue_mbed 0:4d4c5ea17d86 123 }
s_inoue_mbed 0:4d4c5ea17d86 124
s_inoue_mbed 0:4d4c5ea17d86 125 // Extracting temperature data from the received data
s_inoue_mbed 9:056d1e9b428c 126 int DHT11::readTemperature(void)
s_inoue_mbed 0:4d4c5ea17d86 127 {
s_inoue_mbed 9:056d1e9b428c 128 return (data & 0x0000ff0000) >> 16;
s_inoue_mbed 0:4d4c5ea17d86 129 }
s_inoue_mbed 0:4d4c5ea17d86 130
s_inoue_mbed 0:4d4c5ea17d86 131 // Initialization of variables
s_inoue_mbed 0:4d4c5ea17d86 132 void DHT11::init(void)
s_inoue_mbed 0:4d4c5ea17d86 133 {
s_inoue_mbed 0:4d4c5ea17d86 134 t_pulse_us = 0;
s_inoue_mbed 0:4d4c5ea17d86 135 data = 0;
s_inoue_mbed 0:4d4c5ea17d86 136 chksum = 0;
s_inoue_mbed 0:4d4c5ea17d86 137 cnt = 0;
s_inoue_mbed 0:4d4c5ea17d86 138 wdt = 0;
s_inoue_mbed 0:4d4c5ea17d86 139 eod = false;
s_inoue_mbed 9:056d1e9b428c 140 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 141 }
s_inoue_mbed 0:4d4c5ea17d86 142
s_inoue_mbed 0:4d4c5ea17d86 143 void DHT11::pos_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 144 {
s_inoue_mbed 0:4d4c5ea17d86 145 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 146 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 147
s_inoue_mbed 0:4d4c5ea17d86 148 // Initializing the Timer
s_inoue_mbed 0:4d4c5ea17d86 149 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 150
s_inoue_mbed 0:4d4c5ea17d86 151 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 152 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 153 }
s_inoue_mbed 0:4d4c5ea17d86 154
s_inoue_mbed 0:4d4c5ea17d86 155 void DHT11::neg_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 156 {
s_inoue_mbed 0:4d4c5ea17d86 157 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 158 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 159
s_inoue_mbed 8:160047ca45bf 160 // Reading the positive pulse width
s_inoue_mbed 0:4d4c5ea17d86 161 t_pulse_us = t.read_us();
s_inoue_mbed 0:4d4c5ea17d86 162
s_inoue_mbed 9:056d1e9b428c 163 // Detecting 0 if the pulse width ranges around 25 us
s_inoue_mbed 9:056d1e9b428c 164 if (25 - t_tol_pulse <= t_pulse_us && t_pulse_us <= 30 + t_tol_pulse) {
s_inoue_mbed 0:4d4c5ea17d86 165 // Shifting the data buffer and not adding 1 (because this bit is zero)
s_inoue_mbed 0:4d4c5ea17d86 166 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 167
s_inoue_mbed 0:4d4c5ea17d86 168 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 169 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 170 }
s_inoue_mbed 0:4d4c5ea17d86 171
s_inoue_mbed 9:056d1e9b428c 172 // Detecting 1 if the pulse width ranges from 70 us
s_inoue_mbed 9:056d1e9b428c 173 else if (70 - t_tol_pulse <= t_pulse_us && t_pulse_us <= 70 + t_tol_pulse) {
s_inoue_mbed 0:4d4c5ea17d86 174 // Shifting the data buffer and adding 1 (because this bit is one)
s_inoue_mbed 0:4d4c5ea17d86 175 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 176 data++;
s_inoue_mbed 0:4d4c5ea17d86 177
s_inoue_mbed 0:4d4c5ea17d86 178 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 179 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 180 }
s_inoue_mbed 0:4d4c5ea17d86 181
s_inoue_mbed 0:4d4c5ea17d86 182 // Detecting the end of Data
s_inoue_mbed 0:4d4c5ea17d86 183 if (cnt < 40) {
s_inoue_mbed 0:4d4c5ea17d86 184 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 185 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 186 } else {
s_inoue_mbed 0:4d4c5ea17d86 187 eod = true;
s_inoue_mbed 0:4d4c5ea17d86 188 }
s_inoue_mbed 0:4d4c5ea17d86 189 }