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@8:160047ca45bf, 2014-09-10 (annotated)

Committer:
s_inoue_mbed
Date:
Wed Sep 10 18:00:31 2014 +0000
Revision:
8:160047ca45bf
Parent:
7:50f5c8efd967
Child:
9:056d1e9b428c
Pulse widths have been changed.

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 8:160047ca45bf 39 // Sending start signal, low signal for 20 ms
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 8:160047ca45bf 45 } while (t.read_ms() < 20);
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 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 76
s_inoue_mbed 0:4d4c5ea17d86 77 do {
s_inoue_mbed 0:4d4c5ea17d86 78 wait_us(100);
s_inoue_mbed 0:4d4c5ea17d86 79 if (wdt > 50) {
s_inoue_mbed 0:4d4c5ea17d86 80 return WATCHDOG_ERR;
s_inoue_mbed 0:4d4c5ea17d86 81 }
s_inoue_mbed 0:4d4c5ea17d86 82 wdt++;
s_inoue_mbed 0:4d4c5ea17d86 83 } while (eod == false);
s_inoue_mbed 0:4d4c5ea17d86 84
s_inoue_mbed 0:4d4c5ea17d86 85 // Calculating the check sum
s_inoue_mbed 0:4d4c5ea17d86 86 chksum = ((data & 0xff00000000) >> 32)
s_inoue_mbed 0:4d4c5ea17d86 87 + ((data & 0x00ff000000) >> 24)
s_inoue_mbed 0:4d4c5ea17d86 88 + ((data & 0x0000ff0000) >> 16)
s_inoue_mbed 0:4d4c5ea17d86 89 + ((data & 0x000000ff00) >> 8);
s_inoue_mbed 0:4d4c5ea17d86 90 if (chksum != (data & 0x00000000ff)) {
s_inoue_mbed 0:4d4c5ea17d86 91 return CHKSUM_ERR;
s_inoue_mbed 0:4d4c5ea17d86 92 } else {
s_inoue_mbed 0:4d4c5ea17d86 93 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 94 first_time = false;
s_inoue_mbed 0:4d4c5ea17d86 95 return OK;
s_inoue_mbed 0:4d4c5ea17d86 96 }
s_inoue_mbed 0:4d4c5ea17d86 97 }
s_inoue_mbed 0:4d4c5ea17d86 98
s_inoue_mbed 0:4d4c5ea17d86 99 // Extracting humidity data from the received data
s_inoue_mbed 0:4d4c5ea17d86 100 int DHT11::readHumidity()
s_inoue_mbed 0:4d4c5ea17d86 101 {
s_inoue_mbed 0:4d4c5ea17d86 102 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 103 return (data & 0xff00000000) >> 32;
s_inoue_mbed 0:4d4c5ea17d86 104 } else {
s_inoue_mbed 0:4d4c5ea17d86 105 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 106 }
s_inoue_mbed 0:4d4c5ea17d86 107 }
s_inoue_mbed 0:4d4c5ea17d86 108
s_inoue_mbed 0:4d4c5ea17d86 109 // Extracting temperature data from the received data
s_inoue_mbed 0:4d4c5ea17d86 110 int DHT11::readTemperature()
s_inoue_mbed 0:4d4c5ea17d86 111 {
s_inoue_mbed 0:4d4c5ea17d86 112 if (err == OK) {
s_inoue_mbed 0:4d4c5ea17d86 113 return (data & 0x0000ff0000) >> 16;
s_inoue_mbed 0:4d4c5ea17d86 114 } else {
s_inoue_mbed 0:4d4c5ea17d86 115 return 0xffffffff;
s_inoue_mbed 0:4d4c5ea17d86 116 }
s_inoue_mbed 0:4d4c5ea17d86 117 }
s_inoue_mbed 0:4d4c5ea17d86 118
s_inoue_mbed 0:4d4c5ea17d86 119 // Initialization of variables
s_inoue_mbed 0:4d4c5ea17d86 120 void DHT11::init(void)
s_inoue_mbed 0:4d4c5ea17d86 121 {
s_inoue_mbed 0:4d4c5ea17d86 122 t_pulse_us = 0;
s_inoue_mbed 0:4d4c5ea17d86 123 data = 0;
s_inoue_mbed 0:4d4c5ea17d86 124 chksum = 0;
s_inoue_mbed 0:4d4c5ea17d86 125 cnt = 0;
s_inoue_mbed 0:4d4c5ea17d86 126 wdt = 0;
s_inoue_mbed 0:4d4c5ea17d86 127 err = OK;
s_inoue_mbed 0:4d4c5ea17d86 128 eod = false;
s_inoue_mbed 0:4d4c5ea17d86 129 }
s_inoue_mbed 0:4d4c5ea17d86 130
s_inoue_mbed 0:4d4c5ea17d86 131 void DHT11::pos_edge(void)
s_inoue_mbed 0:4d4c5ea17d86 132 {
s_inoue_mbed 0:4d4c5ea17d86 133 // Disabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 134 io_irq.disable_irq();
s_inoue_mbed 0:4d4c5ea17d86 135
s_inoue_mbed 0:4d4c5ea17d86 136 // Initializing the Timer
s_inoue_mbed 0:4d4c5ea17d86 137 t.reset();
s_inoue_mbed 0:4d4c5ea17d86 138
s_inoue_mbed 0:4d4c5ea17d86 139 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 140 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 141 }
s_inoue_mbed 0:4d4c5ea17d86 142
s_inoue_mbed 0:4d4c5ea17d86 143 void DHT11::neg_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 8:160047ca45bf 148 // Reading the positive pulse width
s_inoue_mbed 0:4d4c5ea17d86 149 t_pulse_us = t.read_us();
s_inoue_mbed 0:4d4c5ea17d86 150
s_inoue_mbed 8:160047ca45bf 151 // Detecting 0 if the pulse width ranges from 20 us to 30 us
s_inoue_mbed 0:4d4c5ea17d86 152 if (20 <= t_pulse_us && t_pulse_us <= 30) {
s_inoue_mbed 0:4d4c5ea17d86 153 // Shifting the data buffer and not adding 1 (because this bit is zero)
s_inoue_mbed 0:4d4c5ea17d86 154 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 155
s_inoue_mbed 0:4d4c5ea17d86 156 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 157 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 158 }
s_inoue_mbed 0:4d4c5ea17d86 159
s_inoue_mbed 8:160047ca45bf 160 // Detecting 1 if the pulse width ranges from 60 us to 80 us
s_inoue_mbed 0:4d4c5ea17d86 161 else if (60 <= t_pulse_us && t_pulse_us <= 80) {
s_inoue_mbed 0:4d4c5ea17d86 162 // Shifting the data buffer and adding 1 (because this bit is one)
s_inoue_mbed 0:4d4c5ea17d86 163 data = data << 1;
s_inoue_mbed 0:4d4c5ea17d86 164 data++;
s_inoue_mbed 0:4d4c5ea17d86 165
s_inoue_mbed 0:4d4c5ea17d86 166 // Counting up the bits
s_inoue_mbed 0:4d4c5ea17d86 167 cnt++;
s_inoue_mbed 0:4d4c5ea17d86 168 }
s_inoue_mbed 0:4d4c5ea17d86 169
s_inoue_mbed 0:4d4c5ea17d86 170 // Detecting the end of Data
s_inoue_mbed 0:4d4c5ea17d86 171 if (cnt < 40) {
s_inoue_mbed 0:4d4c5ea17d86 172 // Enabling the interruptions
s_inoue_mbed 0:4d4c5ea17d86 173 io_irq.enable_irq();
s_inoue_mbed 0:4d4c5ea17d86 174 } else {
s_inoue_mbed 0:4d4c5ea17d86 175 eod = true;
s_inoue_mbed 0:4d4c5ea17d86 176 }
s_inoue_mbed 0:4d4c5ea17d86 177 }