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@7:50f5c8efd967, 2014-09-10 (annotated)

Committer:
s_inoue_mbed
Date:
Wed Sep 10 17:48:35 2014 +0000
Revision:
7:50f5c8efd967
Parent:
6:257e2ab66d0f
Child:
8:160047ca45bf
readData() has been simplified.

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 7:50f5c8efd967 46 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 47 io.input();
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 return NOT_PRESENT;
s_inoue_mbed 0:4d4c5ea17d86 56 }
s_inoue_mbed 0:4d4c5ea17d86 57 } while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 58
s_inoue_mbed 0:4d4c5ea17d86 59 // Wainting for the start of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 60 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 61 t.start();
s_inoue_mbed 0:4d4c5ea17d86 62 do {
s_inoue_mbed 0:4d4c5ea17d86 63 if (t.read_us() > 100) {
s_inoue_mbed 0:4d4c5ea17d86 64 io.input();
s_inoue_mbed 0:4d4c5ea17d86 65 return NOT_READY;
s_inoue_mbed 0:4d4c5ea17d86 66 }
s_inoue_mbed 0:4d4c5ea17d86 67 } while (io == 0);
s_inoue_mbed 0:4d4c5ea17d86 68
s_inoue_mbed 0:4d4c5ea17d86 69 // Wainting for the end of the ready signal
s_inoue_mbed 0:4d4c5ea17d86 70 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 71 t.start();
s_inoue_mbed 0:4d4c5ea17d86 72 do {} while (io == 1);
s_inoue_mbed 0:4d4c5ea17d86 73
s_inoue_mbed 0:4d4c5ea17d86 74 // Starting the pulse width sensing
s_inoue_mbed 0:4d4c5ea17d86 75
s_inoue_mbed 0:4d4c5ea17d86 76 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 77
s_inoue_mbed 0:4d4c5ea17d86 78 do {
s_inoue_mbed 0:4d4c5ea17d86 79 wait_us(100);
s_inoue_mbed 0:4d4c5ea17d86 80 if (wdt > 50) {
s_inoue_mbed 0:4d4c5ea17d86 81 return WATCHDOG_ERR;
s_inoue_mbed 0:4d4c5ea17d86 82 }
s_inoue_mbed 0:4d4c5ea17d86 83 wdt++;
s_inoue_mbed 0:4d4c5ea17d86 84 } while (eod == false);
s_inoue_mbed 0:4d4c5ea17d86 85
s_inoue_mbed 0:4d4c5ea17d86 86 // Calculating the check sum
s_inoue_mbed 0:4d4c5ea17d86 87 chksum = ((data & 0xff00000000) >> 32)
s_inoue_mbed 0:4d4c5ea17d86 88 + ((data & 0x00ff000000) >> 24)
s_inoue_mbed 0:4d4c5ea17d86 89 + ((data & 0x0000ff0000) >> 16)
s_inoue_mbed 0:4d4c5ea17d86 90 + ((data & 0x000000ff00) >> 8);
s_inoue_mbed 0:4d4c5ea17d86 91 if (chksum != (data & 0x00000000ff)) {
s_inoue_mbed 0:4d4c5ea17d86 92 io.input();
s_inoue_mbed 0:4d4c5ea17d86 93 io = 1;
s_inoue_mbed 0:4d4c5ea17d86 94 return CHKSUM_ERR;
s_inoue_mbed 0:4d4c5ea17d86 95 } else {
s_inoue_mbed 0:4d4c5ea17d86 96 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 97 first_time = false;
s_inoue_mbed 0:4d4c5ea17d86 98 return OK;
s_inoue_mbed 0:4d4c5ea17d86 99 }
s_inoue_mbed 0:4d4c5ea17d86 100 }
s_inoue_mbed 0:4d4c5ea17d86 101
s_inoue_mbed 0:4d4c5ea17d86 102 // Extracting humidity data from the received data
s_inoue_mbed 0:4d4c5ea17d86 103 int DHT11::readHumidity()
s_inoue_mbed 0:4d4c5ea17d86 104 {
s_inoue_mbed 0:4d4c5ea17d86 105 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 106 return (data & 0xff00000000) >> 32;
s_inoue_mbed 0:4d4c5ea17d86 107 } else {
s_inoue_mbed 0:4d4c5ea17d86 108 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 109 }
s_inoue_mbed 0:4d4c5ea17d86 110 }
s_inoue_mbed 0:4d4c5ea17d86 111
s_inoue_mbed 0:4d4c5ea17d86 112 // Extracting temperature data from the received data
s_inoue_mbed 0:4d4c5ea17d86 113 int DHT11::readTemperature()
s_inoue_mbed 0:4d4c5ea17d86 114 {
s_inoue_mbed 0:4d4c5ea17d86 115 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 116 return (data & 0x0000ff0000) >> 16;
s_inoue_mbed 0:4d4c5ea17d86 117 } else {
s_inoue_mbed 0:4d4c5ea17d86 118 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 119 }
s_inoue_mbed 0:4d4c5ea17d86 120 }
s_inoue_mbed 0:4d4c5ea17d86 121
s_inoue_mbed 0:4d4c5ea17d86 122 // Initialization of variables
s_inoue_mbed 0:4d4c5ea17d86 123 void DHT11::init(void)
s_inoue_mbed 0:4d4c5ea17d86 124 {
s_inoue_mbed 0:4d4c5ea17d86 125 t_pulse_us = 0;
s_inoue_mbed 0:4d4c5ea17d86 126 data = 0;
s_inoue_mbed 0:4d4c5ea17d86 127 chksum = 0;
s_inoue_mbed 0:4d4c5ea17d86 128 cnt = 0;
s_inoue_mbed 0:4d4c5ea17d86 129 wdt = 0;
s_inoue_mbed 0:4d4c5ea17d86 130 err = OK;
s_inoue_mbed 0:4d4c5ea17d86 131 eod = false;
s_inoue_mbed 0:4d4c5ea17d86 132 }
s_inoue_mbed 0:4d4c5ea17d86 133
s_inoue_mbed 0:4d4c5ea17d86 134 void DHT11::pos_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 135 {
s_inoue_mbed 0:4d4c5ea17d86 136 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 137 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 138
s_inoue_mbed 0:4d4c5ea17d86 139 // Initializing the Timer
s_inoue_mbed 0:4d4c5ea17d86 140 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 141
s_inoue_mbed 0:4d4c5ea17d86 142 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 143 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 144 }
s_inoue_mbed 0:4d4c5ea17d86 145
s_inoue_mbed 0:4d4c5ea17d86 146 void DHT11::neg_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 147 {
s_inoue_mbed 0:4d4c5ea17d86 148 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 149 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 150
s_inoue_mbed 0:4d4c5ea17d86 151 // Reading the length of
s_inoue_mbed 0:4d4c5ea17d86 152 t_pulse_us = t.read_us();
s_inoue_mbed 0:4d4c5ea17d86 153
s_inoue_mbed 0:4d4c5ea17d86 154 // Detecting 0 if the pulse width ranges from 26 us to 28 us
s_inoue_mbed 0:4d4c5ea17d86 155 if (20 <= t_pulse_us && t_pulse_us <= 30) {
s_inoue_mbed 0:4d4c5ea17d86 156 // Shifting the data buffer and not adding 1 (because this bit is zero)
s_inoue_mbed 0:4d4c5ea17d86 157 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 158
s_inoue_mbed 0:4d4c5ea17d86 159 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 160 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 161 }
s_inoue_mbed 0:4d4c5ea17d86 162
s_inoue_mbed 0:4d4c5ea17d86 163 // Detecting 1 if the pulse width ranges from 68 us to 72 us
s_inoue_mbed 0:4d4c5ea17d86 164 else if (60 <= t_pulse_us && t_pulse_us <= 80) {
s_inoue_mbed 0:4d4c5ea17d86 165 // Shifting the data buffer and adding 1 (because this bit is one)
s_inoue_mbed 0:4d4c5ea17d86 166 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 167 data++;
s_inoue_mbed 0:4d4c5ea17d86 168
s_inoue_mbed 0:4d4c5ea17d86 169 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 170 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 171 }
s_inoue_mbed 0:4d4c5ea17d86 172
s_inoue_mbed 0:4d4c5ea17d86 173 // Detecting the end of Data
s_inoue_mbed 0:4d4c5ea17d86 174 if (cnt < 40) {
s_inoue_mbed 0:4d4c5ea17d86 175 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 176 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 177 } else {
s_inoue_mbed 0:4d4c5ea17d86 178 eod = true;
s_inoue_mbed 0:4d4c5ea17d86 179 }
s_inoue_mbed 0:4d4c5ea17d86 180 }