lora dht22
Fork of DHT22 by
DHT22.cpp
- Committer:
- misadows
- Date:
- 2017-01-19
- Revision:
- 1:5ba30e683313
- Parent:
- 0:42ffca439fcc
File content as of revision 1:5ba30e683313:
/* DHT22.cpp - DHT22 sensor library Developed by HO WING KIT Modifications by Paul Adams This library is free software; you can redistribute it and / or modify it under the terms of the GNU Leser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRENTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PATRICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Humidity and Temperature Sensor DHT22 info found at http://www.sparkfun.com/products/10167 same as RHT03 http://www.humiditycn.com Version 0.1: 8-Jan-2011 by Ho Wing Kit Version 0.2: 29-Mar-2012 by Paul Adams Additional Credit: All the commenters on http://www.sparkfun.com/products/10167 */ #include "DHT22.h" // This should be 40, but the sensor is adding an extra bit at the start #define DHT22_DATA_BIT_COUNT 41 DHT22::DHT22(PinName Data) { _data = Data; // Set Data Pin _lastReadTime = time(NULL); _lastHumidity = 0; _lastTemperature = DHT22_ERROR_VALUE; } DHT22::~DHT22() { } DHT22_ERROR DHT22::readData() { int i, j, retryCount; int currentTemperature=0; int currentHumidity=0; unsigned int checkSum = 0, csPart1, csPart2, csPart3, csPart4; unsigned int bitTimes[DHT22_DATA_BIT_COUNT]; DHT22_ERROR err = DHT_ERROR_NONE; time_t currentTime = time(NULL); DigitalInOut DATA(_data); for (i = 0; i < DHT22_DATA_BIT_COUNT; i++) { bitTimes[i] = 0; } if (int(currentTime - _lastReadTime) < 2) { printf("DHT22 Error Access Time < 2s\r\n"); err = DHT_ERROR_TOO_QUICK; } retryCount = 0; // Pin needs to start HIGH, wait unit it is HIGH with a timeout do { if (retryCount > 125) { printf("DHT22 Bus busy!\r\n"); err = DHT_BUS_HUNG; } retryCount ++; wait_us(2); } while (DATA==0); // exit on DHT22 return 'High' Signal within 250us // Send the activate pulse // Step 1: MCU send out start signal to DHT22 and DHT22 send // response signal to MCU. // If always signal high-voltage-level, it means DHT22 is not // working properly, please check the electrical connection status. // DATA.output(); // set pin to output data DATA = 0; // MCU send out start signal to DHT22 wait_ms(18); // 18 ms wait (spec: at least 1ms) DATA = 1; // MCU pull up wait_us(40); DATA.input(); // set pin to receive data // Find the start of the ACK Pulse retryCount = 0; do { if (retryCount > 40) { // (Spec is 20-40 us high) printf("DHT22 not responding!\r\n"); err = DHT_ERROR_NOT_PRESENT; } retryCount++; wait_us(1); } while (DATA==1); // Exit on DHT22 pull low within 40us if (err != DHT_ERROR_NONE) { // initialisation failed return err; } wait_us(80); // DHT pull up ready to transmit data /* if (DATA == 0) { printf("DHT22 not ready!"); err = DHT_ERROR_ACK_TOO_LONG; return err; } */ // Reading the 5 byte data stream // Step 2: DHT22 send data to MCU // Start bit -> low volage within 50us (actually could be anything from 35-75us) // 0 -> high volage within 26-28us (actually could be 10-40us) // 1 -> high volage within 70us (actually could be 60-85us) // See http://www.sparkfun.com/products/10167#comment-4f118d6e757b7f536e000000 for (i = 0; i < 5; i++) { for (j = 0; j < 8; j++) { // Instead of relying on the data sheet, just wait while the RHT03 pin is low retryCount = 0; do { if (retryCount > 75) { printf("DHT22 timeout waiting for data!\r\n"); err = DHT_ERROR_DATA_TIMEOUT; } retryCount++; wait_us(1); } while (DATA == 0); // We now wait for 40us wait_us(40); if (DATA == 1) { // If pin is still high, bit value is a 1 bitTimes[i*8+j] = 1; } else { // The bit value is a 0 bitTimes[i*8+j] = 0; } int count = 0; while (DATA == 1 && count < 100) { wait_us(1); // Delay for 1 microsecond count++; } } } // Re-init DHT22 pin DATA.output(); DATA = 1; // Now bitTimes have the actual bits // that were needed to find the end of each data bit // Note: the bits are offset by one from the data sheet, not sure why currentHumidity = 0; currentTemperature = 0; checkSum = 0; // First 16 bits is Humidity for (i=0; i<16; i++) { //printf("bit %d: %d ", i, bitTimes[i+1]); if (bitTimes[i+1] > 0) { currentHumidity |= ( 1 << (15-i)); } } // Second 16 bits is Temperature for (i=0; i<16; i ++) { //printf("bit %d: %d ", i+16, bitTimes[i+17]); if (bitTimes[i+17] > 0) { currentTemperature |= (1 <<(15-i)); } } // Last 8 bit is Checksum for (i=0; i<8; i++) { //printf("bit %d: %d ", i+32, bitTimes[i+33]); if (bitTimes[i+33] > 0) { checkSum |= (1 << (7-i)); } } _lastHumidity = (float(currentHumidity) / 10.0); // if first bit of currentTemperature is 1, it is negative value. if ((currentTemperature & 0x8000)==0x8000) { _lastTemperature = (float(currentTemperature & 0x7FFF) / 10.0) * -1.0; } else { _lastTemperature = float(currentTemperature) / 10.0; } // Calculate Check Sum csPart1 = currentHumidity >> 8; csPart2 = currentHumidity & 0xFF; csPart3 = currentTemperature >> 8; csPart4 = currentTemperature & 0xFF; //if (checkSum == ((csPart1 + csPart2 + csPart3 + csPart4) & 0xFF)) { _lastReadTime = currentTime; //printf("OK-->Temperature:%.1f, Humidity:%.1f\r\n", _lastTemperature, _lastHumidity); err = DHT_ERROR_NONE; /*} else { printf("DHT22 Checksum error!\r\n"); printf("Calculate check sum is %d\r\n",(csPart1 + csPart2 + csPart3 + csPart4) & 0xFF); printf("Reading check sum is %d\r\n",checkSum); err = DHT_ERROR_CHECKSUM; }*/ return err; } float DHT22::getTemperatureC() { return _lastTemperature; } float DHT22::getHumidity() { return _lastHumidity; }