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@6:257e2ab66d0f, 2014-09-10 (annotated)

Committer:
s_inoue_mbed
Date:
Wed Sep 10 17:43:14 2014 +0000
Revision:
6:257e2ab66d0f
Parent:
4:48798b126d93
Child:
7:50f5c8efd967
Reorganized initialization function

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 6:257e2ab66d0f 14 init();
s_inoue_mbed 6:257e2ab66d0f 15 first_time = true;
s_inoue_mbed 0:4d4c5ea17d86 16 }
s_inoue_mbed 0:4d4c5ea17d86 17
s_inoue_mbed 0:4d4c5ea17d86 18 // Destructor
s_inoue_mbed 0:4d4c5ea17d86 19 DHT11::~DHT11(void) {}
s_inoue_mbed 0:4d4c5ea17d86 20
s_inoue_mbed 6:257e2ab66d0f 21 // Reading the data bits from the DHT11
s_inoue_mbed 0:4d4c5ea17d86 22 int DHT11::readData()
s_inoue_mbed 0:4d4c5ea17d86 23 {
s_inoue_mbed 0:4d4c5ea17d86 24 // Initialize
s_inoue_mbed 6:257e2ab66d0f 25 init();
s_inoue_mbed 0:4d4c5ea17d86 26
s_inoue_mbed 0:4d4c5ea17d86 27 // Checking the measurement frequency
s_inoue_mbed 0:4d4c5ea17d86 28 if (t.read_ms() < 2000 & first_time == false) {
s_inoue_mbed 0:4d4c5ea17d86 29 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 30 return TOO_FAST_READ;
s_inoue_mbed 0:4d4c5ea17d86 31 }
s_inoue_mbed 0:4d4c5ea17d86 32
s_inoue_mbed 0:4d4c5ea17d86 33 // Checking the data bus
s_inoue_mbed 0:4d4c5ea17d86 34 if (io == 0) {
s_inoue_mbed 0:4d4c5ea17d86 35 io.input();
s_inoue_mbed 0:4d4c5ea17d86 36 return BUS_BUSY;
s_inoue_mbed 0:4d4c5ea17d86 37 }
s_inoue_mbed 0:4d4c5ea17d86 38
s_inoue_mbed 0:4d4c5ea17d86 39 // Sending start signal
s_inoue_mbed 0:4d4c5ea17d86 40 io.output();
s_inoue_mbed 0:4d4c5ea17d86 41 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 42 t.start();
s_inoue_mbed 0:4d4c5ea17d86 43 do {
s_inoue_mbed 0:4d4c5ea17d86 44 io = 0;
s_inoue_mbed 0:4d4c5ea17d86 45 } while (t.read_ms() < 18);
s_inoue_mbed 0:4d4c5ea17d86 46 io.input();
s_inoue_mbed 0:4d4c5ea17d86 47 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 48
s_inoue_mbed 0:4d4c5ea17d86 49 // Waiting for the start of the response signal
s_inoue_mbed 0:4d4c5ea17d86 50 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 51 t.start();
s_inoue_mbed 0:4d4c5ea17d86 52 do {
s_inoue_mbed 0:4d4c5ea17d86 53 if (t.read_us() > 100) {
s_inoue_mbed 0:4d4c5ea17d86 54 io.input();
s_inoue_mbed 0:4d4c5ea17d86 55 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 56 return NOT_PRESENT;
s_inoue_mbed 0:4d4c5ea17d86 57 }
s_inoue_mbed 0:4d4c5ea17d86 58 } while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 59
s_inoue_mbed 0:4d4c5ea17d86 60 // Wainting for the start of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 61 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 62 t.start();
s_inoue_mbed 0:4d4c5ea17d86 63 do {
s_inoue_mbed 0:4d4c5ea17d86 64 if (t.read_us() > 100) {
s_inoue_mbed 0:4d4c5ea17d86 65 io.input();
s_inoue_mbed 0:4d4c5ea17d86 66 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 67 return NOT_READY;
s_inoue_mbed 0:4d4c5ea17d86 68 }
s_inoue_mbed 0:4d4c5ea17d86 69 } while (io == 0);
s_inoue_mbed 0:4d4c5ea17d86 70
s_inoue_mbed 0:4d4c5ea17d86 71 // Wainting for the end of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 72 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 73 t.start();
s_inoue_mbed 0:4d4c5ea17d86 74 do {} while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 75
s_inoue_mbed 0:4d4c5ea17d86 76 // Starting the pulse width sensing
s_inoue_mbed 0:4d4c5ea17d86 77
s_inoue_mbed 0:4d4c5ea17d86 78 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 79
s_inoue_mbed 0:4d4c5ea17d86 80 do {
s_inoue_mbed 0:4d4c5ea17d86 81 wait_us(100);
s_inoue_mbed 0:4d4c5ea17d86 82 if (wdt > 50) {
s_inoue_mbed 0:4d4c5ea17d86 83 return WATCHDOG_ERR;
s_inoue_mbed 0:4d4c5ea17d86 84 }
s_inoue_mbed 0:4d4c5ea17d86 85 wdt++;
s_inoue_mbed 0:4d4c5ea17d86 86 } while (eod == false);
s_inoue_mbed 0:4d4c5ea17d86 87
s_inoue_mbed 0:4d4c5ea17d86 88 // Calculating the check sum
s_inoue_mbed 0:4d4c5ea17d86 89 chksum = ((data & 0xff00000000) >> 32)
s_inoue_mbed 0:4d4c5ea17d86 90 + ((data & 0x00ff000000) >> 24)
s_inoue_mbed 0:4d4c5ea17d86 91 + ((data & 0x0000ff0000) >> 16)
s_inoue_mbed 0:4d4c5ea17d86 92 + ((data & 0x000000ff00) >> 8);
s_inoue_mbed 0:4d4c5ea17d86 93 if (chksum != (data & 0x00000000ff)) {
s_inoue_mbed 0:4d4c5ea17d86 94 io.input();
s_inoue_mbed 0:4d4c5ea17d86 95 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 96 return CHKSUM_ERR;
s_inoue_mbed 0:4d4c5ea17d86 97 } else {
s_inoue_mbed 0:4d4c5ea17d86 98 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 99 first_time = false;
s_inoue_mbed 0:4d4c5ea17d86 100 return OK;
s_inoue_mbed 0:4d4c5ea17d86 101 }
s_inoue_mbed 0:4d4c5ea17d86 102 }
s_inoue_mbed 0:4d4c5ea17d86 103
s_inoue_mbed 0:4d4c5ea17d86 104 // Extracting humidity data from the received data
s_inoue_mbed 0:4d4c5ea17d86 105 int DHT11::readHumidity()
s_inoue_mbed 0:4d4c5ea17d86 106 {
s_inoue_mbed 0:4d4c5ea17d86 107 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 108 return (data & 0xff00000000) >> 32;
s_inoue_mbed 0:4d4c5ea17d86 109 } else {
s_inoue_mbed 0:4d4c5ea17d86 110 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 111 }
s_inoue_mbed 0:4d4c5ea17d86 112 }
s_inoue_mbed 0:4d4c5ea17d86 113
s_inoue_mbed 0:4d4c5ea17d86 114 // Extracting temperature data from the received data
s_inoue_mbed 0:4d4c5ea17d86 115 int DHT11::readTemperature()
s_inoue_mbed 0:4d4c5ea17d86 116 {
s_inoue_mbed 0:4d4c5ea17d86 117 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 118 return (data & 0x0000ff0000) >> 16;
s_inoue_mbed 0:4d4c5ea17d86 119 } else {
s_inoue_mbed 0:4d4c5ea17d86 120 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 121 }
s_inoue_mbed 0:4d4c5ea17d86 122 }
s_inoue_mbed 0:4d4c5ea17d86 123
s_inoue_mbed 0:4d4c5ea17d86 124 // Initialization of variables
s_inoue_mbed 0:4d4c5ea17d86 125 void DHT11::init(void)
s_inoue_mbed 0:4d4c5ea17d86 126 {
s_inoue_mbed 0:4d4c5ea17d86 127 t_pulse_us = 0;
s_inoue_mbed 0:4d4c5ea17d86 128 data = 0;
s_inoue_mbed 0:4d4c5ea17d86 129 chksum = 0;
s_inoue_mbed 0:4d4c5ea17d86 130 cnt = 0;
s_inoue_mbed 0:4d4c5ea17d86 131 wdt = 0;
s_inoue_mbed 0:4d4c5ea17d86 132 err = OK;
s_inoue_mbed 0:4d4c5ea17d86 133 eod = false;
s_inoue_mbed 0:4d4c5ea17d86 134 }
s_inoue_mbed 0:4d4c5ea17d86 135
s_inoue_mbed 0:4d4c5ea17d86 136 void DHT11::pos_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 137 {
s_inoue_mbed 0:4d4c5ea17d86 138 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 139 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 140
s_inoue_mbed 0:4d4c5ea17d86 141 // Initializing the Timer
s_inoue_mbed 0:4d4c5ea17d86 142 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 143
s_inoue_mbed 0:4d4c5ea17d86 144 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 145 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 146 }
s_inoue_mbed 0:4d4c5ea17d86 147
s_inoue_mbed 0:4d4c5ea17d86 148 void DHT11::neg_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 149 {
s_inoue_mbed 0:4d4c5ea17d86 150 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 151 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 152
s_inoue_mbed 0:4d4c5ea17d86 153 // Reading the length of
s_inoue_mbed 0:4d4c5ea17d86 154 t_pulse_us = t.read_us();
s_inoue_mbed 0:4d4c5ea17d86 155
s_inoue_mbed 0:4d4c5ea17d86 156 // Detecting 0 if the pulse width ranges from 26 us to 28 us
s_inoue_mbed 0:4d4c5ea17d86 157 if (20 <= t_pulse_us && t_pulse_us <= 30) {
s_inoue_mbed 0:4d4c5ea17d86 158 // Shifting the data buffer and not adding 1 (because this bit is zero)
s_inoue_mbed 0:4d4c5ea17d86 159 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 160
s_inoue_mbed 0:4d4c5ea17d86 161 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 162 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 163 }
s_inoue_mbed 0:4d4c5ea17d86 164
s_inoue_mbed 0:4d4c5ea17d86 165 // Detecting 1 if the pulse width ranges from 68 us to 72 us
s_inoue_mbed 0:4d4c5ea17d86 166 else if (60 <= t_pulse_us && t_pulse_us <= 80) {
s_inoue_mbed 0:4d4c5ea17d86 167 // Shifting the data buffer and adding 1 (because this bit is one)
s_inoue_mbed 0:4d4c5ea17d86 168 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 169 data++;
s_inoue_mbed 0:4d4c5ea17d86 170
s_inoue_mbed 0:4d4c5ea17d86 171 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 172 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 173 }
s_inoue_mbed 0:4d4c5ea17d86 174
s_inoue_mbed 0:4d4c5ea17d86 175 // Detecting the end of Data
s_inoue_mbed 0:4d4c5ea17d86 176 if (cnt < 40) {
s_inoue_mbed 0:4d4c5ea17d86 177 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 178 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 179 } else {
s_inoue_mbed 0:4d4c5ea17d86 180 eod = true;
s_inoue_mbed 0:4d4c5ea17d86 181 }
s_inoue_mbed 0:4d4c5ea17d86 182 }