Antulio Morgado / DHT22

Plantilla para crear la libreria DHT para la plataforma FRDM

DHT22.cpp@0:547e68daeb1b, 2011-06-21 (annotated)

Committer:
hwkit
Date:
Tue Jun 21 03:44:05 2011 +0000
Revision:
0:547e68daeb1b
Child:
1:5b20ff4fd227
0.1 - beta test

Who changed what in which revision?

UserRevisionLine numberNew contents of line
hwkit 0:547e68daeb1b 1 /*
hwkit 0:547e68daeb1b 2 DHT22.cpp - DHT22 sensor library
hwkit 0:547e68daeb1b 3 Developed by Ben Adams = 2011
hwkit 0:547e68daeb1b 4
hwkit 0:547e68daeb1b 5 This library is free software; you can redistribute it and / or
hwkit 0:547e68daeb1b 6 modify it under the terms of the GNU Leser General Public
hwkit 0:547e68daeb1b 7 License as published by the Free Software Foundation; either
hwkit 0:547e68daeb1b 8 version 2.1 of the License, or (at your option) any later version.
hwkit 0:547e68daeb1b 9
hwkit 0:547e68daeb1b 10 This library is distributed in the hope that it will be useful,
hwkit 0:547e68daeb1b 11 but WITHOUT ANY WARRENTY; without even the implied warranty of
hwkit 0:547e68daeb1b 12 MERCHANTABILITY or FITNESS FOR A PATRICULAR PURPOSE. See the GNU
hwkit 0:547e68daeb1b 13 Lesser General Public License for more details.
hwkit 0:547e68daeb1b 14
hwkit 0:547e68daeb1b 15 You should have received a copy of the GNU Lesser General Public
hwkit 0:547e68daeb1b 16 License along with this library; if not, write to the Free Software
hwkit 0:547e68daeb1b 17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
hwkit 0:547e68daeb1b 18
hwkit 0:547e68daeb1b 19
hwkit 0:547e68daeb1b 20 Humidity and Temperature Sensor DHT22 info found at
hwkit 0:547e68daeb1b 21 http://www.sparkfun.com/products/10167
hwkit 0:547e68daeb1b 22
hwkit 0:547e68daeb1b 23 Version 0.4: 24-Jan-2011 by Ben Adams
hwkit 0:547e68daeb1b 24 Added return code constants to keywords.txt
hwkit 0:547e68daeb1b 25 Return DHT_ERROR_CHECKSUM on check sum mismatch
hwkit 0:547e68daeb1b 26
hwkit 0:547e68daeb1b 27 Version 0.3: 17-Jan-2011 by Ben Adams
hwkit 0:547e68daeb1b 28 This version reads data
hwkit 0:547e68daeb1b 29 Needs check sum code added at the end of readData
hwkit 0:547e68daeb1b 30
hwkit 0:547e68daeb1b 31 Version 0.2: 16-Jan-2011 by Ben Adams
hwkit 0:547e68daeb1b 32 Changed coding style to match other Arduino Libraries.
hwkit 0:547e68daeb1b 33 This version will not read data either!
hwkit 0:547e68daeb1b 34
hwkit 0:547e68daeb1b 35 */
hwkit 0:547e68daeb1b 36
hwkit 0:547e68daeb1b 37 #include "DHT22.h"
hwkit 0:547e68daeb1b 38
hwkit 0:547e68daeb1b 39 // This should be 40, but the sensor is adding an extra bit at the start
hwkit 0:547e68daeb1b 40 #define DHT22_DATA_BIT_COUNT 41
hwkit 0:547e68daeb1b 41
hwkit 0:547e68daeb1b 42 DHT22::DHT22(PinName Data) {
hwkit 0:547e68daeb1b 43 _data = Data; // Set Data Pin
hwkit 0:547e68daeb1b 44 DigitalInOut VCC(_vcc);
hwkit 0:547e68daeb1b 45 _lastReadTime = time(NULL)-2;
hwkit 0:547e68daeb1b 46 _lastHumidity = 0;
hwkit 0:547e68daeb1b 47 _lastTemperature = DHT22_ERROR_VALUE;
hwkit 0:547e68daeb1b 48 }
hwkit 0:547e68daeb1b 49
hwkit 0:547e68daeb1b 50 DHT22::~DHT22() {
hwkit 0:547e68daeb1b 51 }
hwkit 0:547e68daeb1b 52
hwkit 0:547e68daeb1b 53 DHT22_ERROR DHT22::readData() {
hwkit 0:547e68daeb1b 54 int i, retryCount;
hwkit 0:547e68daeb1b 55 int currentTemperature;
hwkit 0:547e68daeb1b 56 int currentHumidity;
hwkit 0:547e68daeb1b 57 unsigned int checkSum, csPart1, csPart2, csPart3, csPart4;
hwkit 0:547e68daeb1b 58 unsigned int bitTimes[DHT22_DATA_BIT_COUNT];
hwkit 0:547e68daeb1b 59 time_t currentTime;
hwkit 0:547e68daeb1b 60
hwkit 0:547e68daeb1b 61 DigitalInOut DATA(_data);
hwkit 0:547e68daeb1b 62
hwkit 0:547e68daeb1b 63 currentHumidity = 0;
hwkit 0:547e68daeb1b 64 currentTemperature = 0;
hwkit 0:547e68daeb1b 65 checkSum = 0;
hwkit 0:547e68daeb1b 66 currentTime = time(NULL);
hwkit 0:547e68daeb1b 67 for (i = 0; i < DHT22_DATA_BIT_COUNT; i++) {
hwkit 0:547e68daeb1b 68 bitTimes[i] = 0;
hwkit 0:547e68daeb1b 69 }
hwkit 0:547e68daeb1b 70 if (currentTime - _lastReadTime < 2) {
hwkit 0:547e68daeb1b 71 // Caller needs to wait 2 seconds between each call to read Data
hwkit 0:547e68daeb1b 72 return DHT_ERROR_TOOQUICK;
hwkit 0:547e68daeb1b 73 }
hwkit 0:547e68daeb1b 74 _lastReadTime = currentTime;
hwkit 0:547e68daeb1b 75 retryCount = 0;
hwkit 0:547e68daeb1b 76 // Pin needs to start HIGH, wait unit it is HIGH with a timeout
hwkit 0:547e68daeb1b 77 do {
hwkit 0:547e68daeb1b 78 if (retryCount > 125) {
hwkit 0:547e68daeb1b 79 return DHT_BUS_HUNG;
hwkit 0:547e68daeb1b 80 }
hwkit 0:547e68daeb1b 81 retryCount ++;
hwkit 0:547e68daeb1b 82 wait_us(2);
hwkit 0:547e68daeb1b 83 } while (DATA==1);
hwkit 0:547e68daeb1b 84 // Send the activate pulse
hwkit 0:547e68daeb1b 85 DATA = 0; // MCU send out start signal to DHT22
hwkit 0:547e68daeb1b 86 wait_us(1100); // 1.1 ms
hwkit 0:547e68daeb1b 87 // Find the start of the ACK Pulse
hwkit 0:547e68daeb1b 88 retryCount = 0;
hwkit 0:547e68daeb1b 89 do {
hwkit 0:547e68daeb1b 90 if (retryCount > 25) {// (Spec is 20 to 40 us, 25*2 == 50us
hwkit 0:547e68daeb1b 91 return DHT_ERROR_NOT_PRESENT;
hwkit 0:547e68daeb1b 92 }
hwkit 0:547e68daeb1b 93 retryCount ++;
hwkit 0:547e68daeb1b 94 wait_us(2);
hwkit 0:547e68daeb1b 95 } while (DATA==1);
hwkit 0:547e68daeb1b 96 // Find the end of the ACK Pulse
hwkit 0:547e68daeb1b 97 retryCount = 0;
hwkit 0:547e68daeb1b 98 do {
hwkit 0:547e68daeb1b 99 if (retryCount > 50) {// (Spec is 80 us, 50 * 2 == 100us)
hwkit 0:547e68daeb1b 100 return DHT_ERROR_ACK_TOO_LONG;
hwkit 0:547e68daeb1b 101 }
hwkit 0:547e68daeb1b 102 retryCount++;
hwkit 0:547e68daeb1b 103 wait_us(2);
hwkit 0:547e68daeb1b 104 } while (DATA==0);
hwkit 0:547e68daeb1b 105 // Read the 40 bit data stream
hwkit 0:547e68daeb1b 106 for (i=0; i < DHT22_DATA_BIT_COUNT; i++) {
hwkit 0:547e68daeb1b 107 retryCount = 0;
hwkit 0:547e68daeb1b 108 do {
hwkit 0:547e68daeb1b 109 if (retryCount > 35) { // spec is 50 u, 35*2 = 70 us
hwkit 0:547e68daeb1b 110 return DHT_ERROR_SYNC_TIMEOUT;
hwkit 0:547e68daeb1b 111 }
hwkit 0:547e68daeb1b 112 retryCount ++;
hwkit 0:547e68daeb1b 113 wait_us(2);
hwkit 0:547e68daeb1b 114 } while (DATA==1);
hwkit 0:547e68daeb1b 115 // Measure the width of the data pulse
hwkit 0:547e68daeb1b 116 retryCount = 0;
hwkit 0:547e68daeb1b 117 do {
hwkit 0:547e68daeb1b 118 if (retryCount > 50) { // spec is 80us, 50*2 == 100us
hwkit 0:547e68daeb1b 119 return DHT_ERROR_DATA_TIMEOUT;
hwkit 0:547e68daeb1b 120 }
hwkit 0:547e68daeb1b 121 retryCount++;
hwkit 0:547e68daeb1b 122 wait_us(2);
hwkit 0:547e68daeb1b 123 } while (DATA==0);
hwkit 0:547e68daeb1b 124 bitTimes[i] = retryCount;
hwkit 0:547e68daeb1b 125 }
hwkit 0:547e68daeb1b 126
hwkit 0:547e68daeb1b 127 // Now bitTimes have the number of retries (us *2)
hwkit 0:547e68daeb1b 128 // that were needed to find the end of each data bit
hwkit 0:547e68daeb1b 129 // Spec: 0 is 26 to 28 us
hwkit 0:547e68daeb1b 130 // Spec: 1 is 70 us
hwkit 0:547e68daeb1b 131 // bitTimes[x] <= 11 is a 0
hwkit 0:547e68daeb1b 132 // bitTimes[x] > 11 is a 1
hwkit 0:547e68daeb1b 133 // Note: the bits are offset by one from the data sheet, not sure why
hwkit 0:547e68daeb1b 134 for (i=0; i<16; i++) {
hwkit 0:547e68daeb1b 135 if (bitTimes[i+1] > 11) {
hwkit 0:547e68daeb1b 136 currentHumidity |= ( 1 << (15-i));
hwkit 0:547e68daeb1b 137 }
hwkit 0:547e68daeb1b 138 }
hwkit 0:547e68daeb1b 139
hwkit 0:547e68daeb1b 140 for (i=0; i<16; i ++) {
hwkit 0:547e68daeb1b 141 if (bitTimes[i+17] > 11) {
hwkit 0:547e68daeb1b 142 currentTemperature |= (1 <<(15-i));
hwkit 0:547e68daeb1b 143 }
hwkit 0:547e68daeb1b 144 }
hwkit 0:547e68daeb1b 145
hwkit 0:547e68daeb1b 146 for (i=0; i<8; i++) {
hwkit 0:547e68daeb1b 147 if (bitTimes[i+33]>11) {
hwkit 0:547e68daeb1b 148 checkSum |= (1 << (7-i));
hwkit 0:547e68daeb1b 149 }
hwkit 0:547e68daeb1b 150 }
hwkit 0:547e68daeb1b 151 _lastHumidity = (float(currentHumidity & 0x7FFF) / 10.0);
hwkit 0:547e68daeb1b 152 if (currentTemperature &= 0x8000) {
hwkit 0:547e68daeb1b 153 currentTemperature &= 0x7FFF;
hwkit 0:547e68daeb1b 154 _lastTemperature = (float(currentTemperature) / 10.0) * -1.0;
hwkit 0:547e68daeb1b 155 } else {
hwkit 0:547e68daeb1b 156 _lastTemperature = float(currentTemperature) / 10.0;
hwkit 0:547e68daeb1b 157 }
hwkit 0:547e68daeb1b 158
hwkit 0:547e68daeb1b 159 // Calculate Check Sum
hwkit 0:547e68daeb1b 160 csPart1 = currentHumidity >> 8;
hwkit 0:547e68daeb1b 161 csPart2 = currentHumidity & 0xFF;
hwkit 0:547e68daeb1b 162 csPart3 = currentTemperature >> 8;
hwkit 0:547e68daeb1b 163 csPart4 = currentTemperature & 0xFF;
hwkit 0:547e68daeb1b 164 if (checkSum == ((csPart1 + csPart2 + csPart3 + csPart4) & 0xFF)) {
hwkit 0:547e68daeb1b 165 return DHT_ERROR_NONE;
hwkit 0:547e68daeb1b 166 }
hwkit 0:547e68daeb1b 167 return DHT_ERROR_CHECKSUM;
hwkit 0:547e68daeb1b 168 }
hwkit 0:547e68daeb1b 169
hwkit 0:547e68daeb1b 170 float DHT22::getTemperatureC() {
hwkit 0:547e68daeb1b 171 return _lastTemperature;
hwkit 0:547e68daeb1b 172 }
hwkit 0:547e68daeb1b 173
hwkit 0:547e68daeb1b 174 float DHT22::getHumidity() {
hwkit 0:547e68daeb1b 175 return _lastHumidity;
hwkit 0:547e68daeb1b 176 }