FRA221_2015 / Mbed 2 deprecated 1A_PROJECT_DIGITAL

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Dependencies:   mbed

Fork of 1A_PROJECT_DIGITAL by Jakkapan Keawsalak

DHT22.cpp@0:ede9cc7e508b, 2015-12-08 (annotated)

Committer:
gamezajad
Date:
Tue Dec 08 19:25:47 2015 +0000
Revision:
0:ede9cc7e508b
1A

Who changed what in which revision?

UserRevisionLine numberNew contents of line
gamezajad 0:ede9cc7e508b 1
gamezajad 0:ede9cc7e508b 2 #include "DHT22.h"
gamezajad 0:ede9cc7e508b 3 #define DHT22_DATA_BIT_COUNT 41
gamezajad 0:ede9cc7e508b 4
gamezajad 0:ede9cc7e508b 5 DHT22::DHT22(PinName Data) {
gamezajad 0:ede9cc7e508b 6
gamezajad 0:ede9cc7e508b 7 _data = Data; // Set Data Pin
gamezajad 0:ede9cc7e508b 8 _lastReadTime = time(NULL);
gamezajad 0:ede9cc7e508b 9 _lastHumidity = 0;
gamezajad 0:ede9cc7e508b 10 _lastTemperature = DHT22_ERROR_VALUE;
gamezajad 0:ede9cc7e508b 11 }
gamezajad 0:ede9cc7e508b 12
gamezajad 0:ede9cc7e508b 13 DHT22::~DHT22() {
gamezajad 0:ede9cc7e508b 14 }
gamezajad 0:ede9cc7e508b 15
gamezajad 0:ede9cc7e508b 16 DHT22_ERROR DHT22::readData() {
gamezajad 0:ede9cc7e508b 17 int i, j, retryCount;
gamezajad 0:ede9cc7e508b 18 int currentTemperature=0;
gamezajad 0:ede9cc7e508b 19 int currentHumidity=0;
gamezajad 0:ede9cc7e508b 20 unsigned int checkSum = 0, csPart1, csPart2, csPart3, csPart4;
gamezajad 0:ede9cc7e508b 21 unsigned int bitTimes[DHT22_DATA_BIT_COUNT];
gamezajad 0:ede9cc7e508b 22 DHT22_ERROR err = DHT_ERROR_NONE;
gamezajad 0:ede9cc7e508b 23 time_t currentTime = time(NULL);
gamezajad 0:ede9cc7e508b 24
gamezajad 0:ede9cc7e508b 25 DigitalInOut DATA(_data);
gamezajad 0:ede9cc7e508b 26
gamezajad 0:ede9cc7e508b 27 for (i = 0; i < DHT22_DATA_BIT_COUNT; i++) {
gamezajad 0:ede9cc7e508b 28 bitTimes[i] = 0;
gamezajad 0:ede9cc7e508b 29 }
gamezajad 0:ede9cc7e508b 30
gamezajad 0:ede9cc7e508b 31 if (int(currentTime - _lastReadTime) < 2) {
gamezajad 0:ede9cc7e508b 32 err = DHT_ERROR_TOO_QUICK;
gamezajad 0:ede9cc7e508b 33 }
gamezajad 0:ede9cc7e508b 34 retryCount = 0;
gamezajad 0:ede9cc7e508b 35
gamezajad 0:ede9cc7e508b 36 do {
gamezajad 0:ede9cc7e508b 37 if (retryCount > 125) {
gamezajad 0:ede9cc7e508b 38 printf("DHT22 Bus busy!");
gamezajad 0:ede9cc7e508b 39 err = DHT_BUS_HUNG;
gamezajad 0:ede9cc7e508b 40 }
gamezajad 0:ede9cc7e508b 41 retryCount ++;
gamezajad 0:ede9cc7e508b 42 wait_us(2);
gamezajad 0:ede9cc7e508b 43 } while (DATA==0); // exit on DHT22 return 'High' Signal within 250us
gamezajad 0:ede9cc7e508b 44
gamezajad 0:ede9cc7e508b 45 // Send the activate pulse
gamezajad 0:ede9cc7e508b 46 // Step 1: MCU send out start signal to DHT22 and DHT22 send
gamezajad 0:ede9cc7e508b 47 // response signal to MCU.
gamezajad 0:ede9cc7e508b 48 // If always signal high-voltage-level, it means DHT22 is not
gamezajad 0:ede9cc7e508b 49 // working properly, please check the electrical connection status.
gamezajad 0:ede9cc7e508b 50 //
gamezajad 0:ede9cc7e508b 51 DATA.output(); // set pin to output data
gamezajad 0:ede9cc7e508b 52 DATA = 0; // MCU send out start signal to DHT22
gamezajad 0:ede9cc7e508b 53 wait_ms(18); // 18 ms wait (spec: at least 1ms)
gamezajad 0:ede9cc7e508b 54 DATA = 1; // MCU pull up
gamezajad 0:ede9cc7e508b 55 wait_us(40);
gamezajad 0:ede9cc7e508b 56 DATA.input(); // set pin to receive data
gamezajad 0:ede9cc7e508b 57 // Find the start of the ACK Pulse
gamezajad 0:ede9cc7e508b 58 retryCount = 0;
gamezajad 0:ede9cc7e508b 59 do {
gamezajad 0:ede9cc7e508b 60 if (retryCount > 40) { // (Spec is 20-40 us high)
gamezajad 0:ede9cc7e508b 61 printf("DHT22 not responding!");
gamezajad 0:ede9cc7e508b 62 err = DHT_ERROR_NOT_PRESENT;
gamezajad 0:ede9cc7e508b 63 }
gamezajad 0:ede9cc7e508b 64 retryCount++;
gamezajad 0:ede9cc7e508b 65 wait_us(1);
gamezajad 0:ede9cc7e508b 66 } while (DATA==1); // Exit on DHT22 pull low within 40us
gamezajad 0:ede9cc7e508b 67 if (err != DHT_ERROR_NONE) {
gamezajad 0:ede9cc7e508b 68 // initialisation failed
gamezajad 0:ede9cc7e508b 69 return err;
gamezajad 0:ede9cc7e508b 70 }
gamezajad 0:ede9cc7e508b 71 wait_us(80); // DHT pull up ready to transmit data
gamezajad 0:ede9cc7e508b 72
gamezajad 0:ede9cc7e508b 73 /*
gamezajad 0:ede9cc7e508b 74 if (DATA == 0) {
gamezajad 0:ede9cc7e508b 75 printf("DHT22 not ready!");
gamezajad 0:ede9cc7e508b 76 err = DHT_ERROR_ACK_TOO_LONG;
gamezajad 0:ede9cc7e508b 77 return err;
gamezajad 0:ede9cc7e508b 78 }
gamezajad 0:ede9cc7e508b 79 */
gamezajad 0:ede9cc7e508b 80
gamezajad 0:ede9cc7e508b 81 // Reading the 5 byte data stream
gamezajad 0:ede9cc7e508b 82 // Step 2: DHT22 send data to MCU
gamezajad 0:ede9cc7e508b 83 // Start bit -> low volage within 50us (actually could be anything from 35-75us)
gamezajad 0:ede9cc7e508b 84 // 0 -> high volage within 26-28us (actually could be 10-40us)
gamezajad 0:ede9cc7e508b 85 // 1 -> high volage within 70us (actually could be 60-85us)
gamezajad 0:ede9cc7e508b 86 // See http://www.sparkfun.com/products/10167#comment-4f118d6e757b7f536e000000
gamezajad 0:ede9cc7e508b 87
gamezajad 0:ede9cc7e508b 88
gamezajad 0:ede9cc7e508b 89 for (i = 0; i < 5; i++) {
gamezajad 0:ede9cc7e508b 90 for (j = 0; j < 8; j++) {
gamezajad 0:ede9cc7e508b 91 // Instead of relying on the data sheet, just wait while the RHT03 pin is low
gamezajad 0:ede9cc7e508b 92 retryCount = 0;
gamezajad 0:ede9cc7e508b 93 do {
gamezajad 0:ede9cc7e508b 94 if (retryCount > 75) {
gamezajad 0:ede9cc7e508b 95 printf("DHT22 timeout waiting for data!");
gamezajad 0:ede9cc7e508b 96 err = DHT_ERROR_DATA_TIMEOUT;
gamezajad 0:ede9cc7e508b 97 }
gamezajad 0:ede9cc7e508b 98 retryCount++;
gamezajad 0:ede9cc7e508b 99 wait_us(1);
gamezajad 0:ede9cc7e508b 100 } while (DATA == 0);
gamezajad 0:ede9cc7e508b 101 // We now wait for 40us
gamezajad 0:ede9cc7e508b 102 wait_us(40);
gamezajad 0:ede9cc7e508b 103 if (DATA == 1) {
gamezajad 0:ede9cc7e508b 104 // If pin is still high, bit value is a 1
gamezajad 0:ede9cc7e508b 105 bitTimes[i*8+j] = 1;
gamezajad 0:ede9cc7e508b 106 } else {
gamezajad 0:ede9cc7e508b 107 // The bit value is a 0
gamezajad 0:ede9cc7e508b 108 bitTimes[i*8+j] = 0;
gamezajad 0:ede9cc7e508b 109 }
gamezajad 0:ede9cc7e508b 110 int count = 0;
gamezajad 0:ede9cc7e508b 111 while (DATA == 1 && count < 100) {
gamezajad 0:ede9cc7e508b 112 wait_us(1); // Delay for 1 microsecond
gamezajad 0:ede9cc7e508b 113 count++;
gamezajad 0:ede9cc7e508b 114 }
gamezajad 0:ede9cc7e508b 115 }
gamezajad 0:ede9cc7e508b 116 }
gamezajad 0:ede9cc7e508b 117 // Re-init DHT22 pin
gamezajad 0:ede9cc7e508b 118 DATA.output();
gamezajad 0:ede9cc7e508b 119 DATA = 1;
gamezajad 0:ede9cc7e508b 120
gamezajad 0:ede9cc7e508b 121 // Now bitTimes have the actual bits
gamezajad 0:ede9cc7e508b 122 // that were needed to find the end of each data bit
gamezajad 0:ede9cc7e508b 123 // Note: the bits are offset by one from the data sheet, not sure why
gamezajad 0:ede9cc7e508b 124 currentHumidity = 0;
gamezajad 0:ede9cc7e508b 125 currentTemperature = 0;
gamezajad 0:ede9cc7e508b 126 checkSum = 0;
gamezajad 0:ede9cc7e508b 127 // First 16 bits is Humidity
gamezajad 0:ede9cc7e508b 128 for (i=0; i<16; i++) {
gamezajad 0:ede9cc7e508b 129 //printf("bit %d: %d ", i, bitTimes[i+1]);
gamezajad 0:ede9cc7e508b 130 if (bitTimes[i+1] > 0) {
gamezajad 0:ede9cc7e508b 131 currentHumidity |= ( 1 << (15-i));
gamezajad 0:ede9cc7e508b 132 }
gamezajad 0:ede9cc7e508b 133 }
gamezajad 0:ede9cc7e508b 134
gamezajad 0:ede9cc7e508b 135 // Second 16 bits is Temperature
gamezajad 0:ede9cc7e508b 136 for (i=0; i<16; i ++) {
gamezajad 0:ede9cc7e508b 137 //printf("bit %d: %d ", i+16, bitTimes[i+17]);
gamezajad 0:ede9cc7e508b 138 if (bitTimes[i+17] > 0) {
gamezajad 0:ede9cc7e508b 139 currentTemperature |= (1 <<(15-i));
gamezajad 0:ede9cc7e508b 140 }
gamezajad 0:ede9cc7e508b 141 }
gamezajad 0:ede9cc7e508b 142
gamezajad 0:ede9cc7e508b 143 // Last 8 bit is Checksum
gamezajad 0:ede9cc7e508b 144 for (i=0; i<8; i++) {
gamezajad 0:ede9cc7e508b 145 //printf("bit %d: %d ", i+32, bitTimes[i+33]);
gamezajad 0:ede9cc7e508b 146 if (bitTimes[i+33] > 0) {
gamezajad 0:ede9cc7e508b 147 checkSum |= (1 << (7-i));
gamezajad 0:ede9cc7e508b 148 }
gamezajad 0:ede9cc7e508b 149 }
gamezajad 0:ede9cc7e508b 150
gamezajad 0:ede9cc7e508b 151 _lastHumidity = (float(currentHumidity) / 10.0);
gamezajad 0:ede9cc7e508b 152
gamezajad 0:ede9cc7e508b 153 // if first bit of currentTemperature is 1, it is negative value.
gamezajad 0:ede9cc7e508b 154 if ((currentTemperature & 0x8000)==0x8000) {
gamezajad 0:ede9cc7e508b 155 _lastTemperature = (float(currentTemperature & 0x7FFF) / 10.0) * -1.0;
gamezajad 0:ede9cc7e508b 156 } else {
gamezajad 0:ede9cc7e508b 157 _lastTemperature = float(currentTemperature) / 10.0;
gamezajad 0:ede9cc7e508b 158 }
gamezajad 0:ede9cc7e508b 159
gamezajad 0:ede9cc7e508b 160 // Calculate Check Sum
gamezajad 0:ede9cc7e508b 161 csPart1 = currentHumidity >> 8;
gamezajad 0:ede9cc7e508b 162 csPart2 = currentHumidity & 0xFF;
gamezajad 0:ede9cc7e508b 163 csPart3 = currentTemperature >> 8;
gamezajad 0:ede9cc7e508b 164 csPart4 = currentTemperature & 0xFF;
gamezajad 0:ede9cc7e508b 165
gamezajad 0:ede9cc7e508b 166 if (checkSum == ((csPart1 + csPart2 + csPart3 + csPart4) & 0xFF)) {
gamezajad 0:ede9cc7e508b 167 _lastReadTime = currentTime;
gamezajad 0:ede9cc7e508b 168 //printf("OK-->Temperature :: %f , Humidity :: %f\r\n", _lastTemperature, _lastHumidity);
gamezajad 0:ede9cc7e508b 169 err = DHT_ERROR_NONE;
gamezajad 0:ede9cc7e508b 170 printf("\n");
gamezajad 0:ede9cc7e508b 171
gamezajad 0:ede9cc7e508b 172 }
gamezajad 0:ede9cc7e508b 173 else {
gamezajad 0:ede9cc7e508b 174 //printf("DHT22 Checksum error!\n");
gamezajad 0:ede9cc7e508b 175 //printf("Calculate check sum is %d\n",(csPart1 + csPart2 + csPart3 + csPart4) & 0xFF);
gamezajad 0:ede9cc7e508b 176 //printf("Reading check sum is %d\n",checkSum);
gamezajad 0:ede9cc7e508b 177 err = DHT_ERROR_CHECKSUM;
gamezajad 0:ede9cc7e508b 178 printf("\n");
gamezajad 0:ede9cc7e508b 179 }
gamezajad 0:ede9cc7e508b 180
gamezajad 0:ede9cc7e508b 181 return err;
gamezajad 0:ede9cc7e508b 182 }
gamezajad 0:ede9cc7e508b 183
gamezajad 0:ede9cc7e508b 184 float DHT22::getTemperatureC() {
gamezajad 0:ede9cc7e508b 185 return _lastTemperature;
gamezajad 0:ede9cc7e508b 186 }
gamezajad 0:ede9cc7e508b 187
gamezajad 0:ede9cc7e508b 188 float DHT22::getHumidity() {
gamezajad 0:ede9cc7e508b 189 return _lastHumidity;
gamezajad 0:ede9cc7e508b 190 }