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@4:48798b126d93, 2014-09-10 (annotated)

Committer:
s_inoue_mbed
Date:
Wed Sep 10 17:18:28 2014 +0000
Revision:
4:48798b126d93
Parent:
1:95b80cc3f676
Child:
6:257e2ab66d0f
Doxygen documentation has been corrected.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
s_inoue_mbed 4:48798b126d93 1 /*
s_inoue_mbed 4:48798b126d93 2 * Library for the use of the DHT11, a temperature and humidity sensor
s_inoue_mbed 4:48798b126d93 3 * Shigenori Inoue, September 10, 2014
s_inoue_mbed 0:4d4c5ea17d86 4 */
s_inoue_mbed 0:4d4c5ea17d86 5
s_inoue_mbed 0:4d4c5ea17d86 6 #include "DHT11.h"
s_inoue_mbed 0:4d4c5ea17d86 7
s_inoue_mbed 0:4d4c5ea17d86 8 // Constructor
s_inoue_mbed 0:4d4c5ea17d86 9 DHT11::DHT11(PinName pin) : io(pin, PIN_INPUT, OpenDrain, 1), io_irq(pin)
s_inoue_mbed 0:4d4c5ea17d86 10 {
s_inoue_mbed 0:4d4c5ea17d86 11 io_irq.rise(this, &DHT11::pos_edge);
s_inoue_mbed 0:4d4c5ea17d86 12 io_irq.fall(this, &DHT11::neg_edge);
s_inoue_mbed 0:4d4c5ea17d86 13 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 14 init();
s_inoue_mbed 0:4d4c5ea17d86 15 }
s_inoue_mbed 0:4d4c5ea17d86 16
s_inoue_mbed 0:4d4c5ea17d86 17 // Destructor
s_inoue_mbed 0:4d4c5ea17d86 18 DHT11::~DHT11(void) {}
s_inoue_mbed 0:4d4c5ea17d86 19
s_inoue_mbed 0:4d4c5ea17d86 20 // Reading the data bits from DHT11
s_inoue_mbed 0:4d4c5ea17d86 21 int DHT11::readData()
s_inoue_mbed 0:4d4c5ea17d86 22 {
s_inoue_mbed 0:4d4c5ea17d86 23 // Initialize
s_inoue_mbed 0:4d4c5ea17d86 24 eod = false;
s_inoue_mbed 0:4d4c5ea17d86 25 err = OK;
s_inoue_mbed 0:4d4c5ea17d86 26 data = 0;
s_inoue_mbed 0:4d4c5ea17d86 27 cnt = 0;
s_inoue_mbed 0:4d4c5ea17d86 28 wdt = 0;
s_inoue_mbed 0:4d4c5ea17d86 29
s_inoue_mbed 0:4d4c5ea17d86 30 // Checking the measurement frequency
s_inoue_mbed 0:4d4c5ea17d86 31 if (t.read_ms() < 2000 & first_time == false) {
s_inoue_mbed 0:4d4c5ea17d86 32 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 33 return TOO_FAST_READ;
s_inoue_mbed 0:4d4c5ea17d86 34 }
s_inoue_mbed 0:4d4c5ea17d86 35
s_inoue_mbed 0:4d4c5ea17d86 36 // Checking the data bus
s_inoue_mbed 0:4d4c5ea17d86 37 if (io == 0) {
s_inoue_mbed 0:4d4c5ea17d86 38 io.input();
s_inoue_mbed 0:4d4c5ea17d86 39 return BUS_BUSY;
s_inoue_mbed 0:4d4c5ea17d86 40 }
s_inoue_mbed 0:4d4c5ea17d86 41
s_inoue_mbed 0:4d4c5ea17d86 42 // Sending start signal
s_inoue_mbed 0:4d4c5ea17d86 43 io.output();
s_inoue_mbed 0:4d4c5ea17d86 44 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 45 t.start();
s_inoue_mbed 0:4d4c5ea17d86 46 do {
s_inoue_mbed 0:4d4c5ea17d86 47 io = 0;
s_inoue_mbed 0:4d4c5ea17d86 48 } while (t.read_ms() < 18);
s_inoue_mbed 0:4d4c5ea17d86 49 io.input();
s_inoue_mbed 0:4d4c5ea17d86 50 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 51
s_inoue_mbed 0:4d4c5ea17d86 52 // Waiting for the start of the response signal
s_inoue_mbed 0:4d4c5ea17d86 53 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 54 t.start();
s_inoue_mbed 0:4d4c5ea17d86 55 do {
s_inoue_mbed 0:4d4c5ea17d86 56 if (t.read_us() > 100) {
s_inoue_mbed 0:4d4c5ea17d86 57 io.input();
s_inoue_mbed 0:4d4c5ea17d86 58 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 59 return NOT_PRESENT;
s_inoue_mbed 0:4d4c5ea17d86 60 }
s_inoue_mbed 0:4d4c5ea17d86 61 } while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 62
s_inoue_mbed 0:4d4c5ea17d86 63 // Wainting for the start of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 64 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 65 t.start();
s_inoue_mbed 0:4d4c5ea17d86 66 do {
s_inoue_mbed 0:4d4c5ea17d86 67 if (t.read_us() > 100) {
s_inoue_mbed 0:4d4c5ea17d86 68 io.input();
s_inoue_mbed 0:4d4c5ea17d86 69 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 70 return NOT_READY;
s_inoue_mbed 0:4d4c5ea17d86 71 }
s_inoue_mbed 0:4d4c5ea17d86 72 } while (io == 0);
s_inoue_mbed 0:4d4c5ea17d86 73
s_inoue_mbed 0:4d4c5ea17d86 74 // Wainting for the end of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 75 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 76 t.start();
s_inoue_mbed 0:4d4c5ea17d86 77 do {} while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 78
s_inoue_mbed 0:4d4c5ea17d86 79 // Starting the pulse width sensing
s_inoue_mbed 0:4d4c5ea17d86 80
s_inoue_mbed 0:4d4c5ea17d86 81 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 82
s_inoue_mbed 0:4d4c5ea17d86 83 do {
s_inoue_mbed 0:4d4c5ea17d86 84 wait_us(100);
s_inoue_mbed 0:4d4c5ea17d86 85 if (wdt > 50) {
s_inoue_mbed 0:4d4c5ea17d86 86 return WATCHDOG_ERR;
s_inoue_mbed 0:4d4c5ea17d86 87 }
s_inoue_mbed 0:4d4c5ea17d86 88 wdt++;
s_inoue_mbed 0:4d4c5ea17d86 89 } while (eod == false);
s_inoue_mbed 0:4d4c5ea17d86 90
s_inoue_mbed 0:4d4c5ea17d86 91 // Calculating the check sum
s_inoue_mbed 0:4d4c5ea17d86 92 chksum = ((data & 0xff00000000) >> 32)
s_inoue_mbed 0:4d4c5ea17d86 93 + ((data & 0x00ff000000) >> 24)
s_inoue_mbed 0:4d4c5ea17d86 94 + ((data & 0x0000ff0000) >> 16)
s_inoue_mbed 0:4d4c5ea17d86 95 + ((data & 0x000000ff00) >> 8);
s_inoue_mbed 0:4d4c5ea17d86 96 if (chksum != (data & 0x00000000ff)) {
s_inoue_mbed 0:4d4c5ea17d86 97 io.input();
s_inoue_mbed 0:4d4c5ea17d86 98 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 99 return CHKSUM_ERR;
s_inoue_mbed 0:4d4c5ea17d86 100 } else {
s_inoue_mbed 0:4d4c5ea17d86 101 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 102 first_time = false;
s_inoue_mbed 0:4d4c5ea17d86 103 return OK;
s_inoue_mbed 0:4d4c5ea17d86 104 }
s_inoue_mbed 0:4d4c5ea17d86 105 }
s_inoue_mbed 0:4d4c5ea17d86 106
s_inoue_mbed 0:4d4c5ea17d86 107 // Extracting humidity data from the received data
s_inoue_mbed 0:4d4c5ea17d86 108 int DHT11::readHumidity()
s_inoue_mbed 0:4d4c5ea17d86 109 {
s_inoue_mbed 0:4d4c5ea17d86 110 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 111 return (data & 0xff00000000) >> 32;
s_inoue_mbed 0:4d4c5ea17d86 112 } else {
s_inoue_mbed 0:4d4c5ea17d86 113 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 114 }
s_inoue_mbed 0:4d4c5ea17d86 115 }
s_inoue_mbed 0:4d4c5ea17d86 116
s_inoue_mbed 0:4d4c5ea17d86 117 // Extracting temperature data from the received data
s_inoue_mbed 0:4d4c5ea17d86 118 int DHT11::readTemperature()
s_inoue_mbed 0:4d4c5ea17d86 119 {
s_inoue_mbed 0:4d4c5ea17d86 120 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 121 return (data & 0x0000ff0000) >> 16;
s_inoue_mbed 0:4d4c5ea17d86 122 } else {
s_inoue_mbed 0:4d4c5ea17d86 123 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 124 }
s_inoue_mbed 0:4d4c5ea17d86 125 }
s_inoue_mbed 0:4d4c5ea17d86 126
s_inoue_mbed 0:4d4c5ea17d86 127 // Initialization of variables
s_inoue_mbed 0:4d4c5ea17d86 128 void DHT11::init(void)
s_inoue_mbed 0:4d4c5ea17d86 129 {
s_inoue_mbed 0:4d4c5ea17d86 130 t_pulse_us = 0;
s_inoue_mbed 0:4d4c5ea17d86 131 first_time = true;
s_inoue_mbed 0:4d4c5ea17d86 132 data = 0;
s_inoue_mbed 0:4d4c5ea17d86 133 chksum = 0;
s_inoue_mbed 0:4d4c5ea17d86 134 cnt = 0;
s_inoue_mbed 0:4d4c5ea17d86 135 wdt = 0;
s_inoue_mbed 0:4d4c5ea17d86 136 err = OK;
s_inoue_mbed 0:4d4c5ea17d86 137 eod = false;
s_inoue_mbed 0:4d4c5ea17d86 138 }
s_inoue_mbed 0:4d4c5ea17d86 139
s_inoue_mbed 0:4d4c5ea17d86 140 void DHT11::pos_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 141 {
s_inoue_mbed 0:4d4c5ea17d86 142 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 143 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 144
s_inoue_mbed 0:4d4c5ea17d86 145 // Initializing the Timer
s_inoue_mbed 0:4d4c5ea17d86 146 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 147
s_inoue_mbed 0:4d4c5ea17d86 148 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 149 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 150 }
s_inoue_mbed 0:4d4c5ea17d86 151
s_inoue_mbed 0:4d4c5ea17d86 152 void DHT11::neg_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 153 {
s_inoue_mbed 0:4d4c5ea17d86 154 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 155 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 156
s_inoue_mbed 0:4d4c5ea17d86 157 // Reading the length of
s_inoue_mbed 0:4d4c5ea17d86 158 t_pulse_us = t.read_us();
s_inoue_mbed 0:4d4c5ea17d86 159
s_inoue_mbed 0:4d4c5ea17d86 160 // Detecting 0 if the pulse width ranges from 26 us to 28 us
s_inoue_mbed 0:4d4c5ea17d86 161 if (20 <= t_pulse_us && t_pulse_us <= 30) {
s_inoue_mbed 0:4d4c5ea17d86 162 // Shifting the data buffer and not adding 1 (because this bit is zero)
s_inoue_mbed 0:4d4c5ea17d86 163 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 164
s_inoue_mbed 0:4d4c5ea17d86 165 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 166 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 167 }
s_inoue_mbed 0:4d4c5ea17d86 168
s_inoue_mbed 0:4d4c5ea17d86 169 // Detecting 1 if the pulse width ranges from 68 us to 72 us
s_inoue_mbed 0:4d4c5ea17d86 170 else if (60 <= t_pulse_us && t_pulse_us <= 80) {
s_inoue_mbed 0:4d4c5ea17d86 171 // Shifting the data buffer and adding 1 (because this bit is one)
s_inoue_mbed 0:4d4c5ea17d86 172 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 173 data++;
s_inoue_mbed 0:4d4c5ea17d86 174
s_inoue_mbed 0:4d4c5ea17d86 175 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 176 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 177 }
s_inoue_mbed 0:4d4c5ea17d86 178
s_inoue_mbed 0:4d4c5ea17d86 179 // Detecting the end of Data
s_inoue_mbed 0:4d4c5ea17d86 180 if (cnt < 40) {
s_inoue_mbed 0:4d4c5ea17d86 181 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 182 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 183 } else {
s_inoue_mbed 0:4d4c5ea17d86 184 eod = true;
s_inoue_mbed 0:4d4c5ea17d86 185 }
s_inoue_mbed 0:4d4c5ea17d86 186 }