Shigenori Inoue / DHT11

A library for the use of DHT11, a temperature and humidity sensor

Dependents:   DHT11_Hello_World IBMIoTClientEthernetExample_W5200 AutoPlants PB_Emma_Ethernet ... more

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 }