Serial printf removed in other to use the nRF52 without BLE Serial
Fork of DHT22 by
DHT22.cpp
- Committer:
- DuyLionTran
- Date:
- 2017-11-03
- Revision:
- 3:78e428144d16
- Parent:
- 2:340957cc8fef
File content as of revision 3:78e428144d16:
/* DHT22.cpp - DHT22 sensor library Developed by HO WING KIT 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 Beata test */ #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, retryCount; int currentTemperature=0; int currentHumidity=0; unsigned int checkSum = 0, csPart1, csPart2, csPart3, csPart4; unsigned int bitTimes[DHT22_DATA_BIT_COUNT]; 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) { return DHT_ERROR_TOOQUICK; } retryCount = 0; // Pin needs to start HIGH, wait unit it is HIGH with a timeout do { if (retryCount > 125) { return DHT_BUS_HUNG; } retryCount ++; wait_us(2); } while (DATA==0); // exit on DHT22 retrun '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, plesee check the electrical connection status. // DATA = 0; // MCU send out start signal to DHT22 wait_us(1100); // 1.1 ms DATA = 1; // MCU pull up wait_us(30); // 30 us // Find the start of the ACK Pulse retryCount = 0; do { if (retryCount > 40) {// (Spec is 80 us, 40*2 == 80us return DHT_ERROR_NOT_PRESENT; } retryCount ++; wait_us(2); } while (DATA==1); // Exit on DHT22 pull low within 80us // Find the last of the ACK Pulse retryCount = 0; do { if (retryCount > 40) {// (Spec is 80 us, 40 * 2 == 100us) return DHT_ERROR_ACK_TOO_LONG; } retryCount++; wait_us(2); } while (DATA==0); // Exit on DHT22 pull high within 80us // Reading the 40 bit data stream // Step 2: DHT22 send data to MCU // Start bit -> low volage within 50us // 0 -> high volage within 26-28 us // 1 -> high volage within 70us // for (i=0; i < DHT22_DATA_BIT_COUNT; i++) { retryCount = 0; do { // Getting start bit signal if (retryCount > 25) { // spec is 50 u, 25*2 = 50 us return DHT_ERROR_SYNC_TIMEOUT; } retryCount ++; wait_us(2); } while (DATA==0); // Exit on high volage within 50us // Measure the width of the data pulse retryCount = 0; do { if (retryCount > 40) { // spec is 80us, 50*2 == 100us return DHT_ERROR_DATA_TIMEOUT; } retryCount++; wait_us(2); } while (DATA==1); // Exit on low volage below 80us bitTimes[i] = retryCount; // Assign bitTimes in us } // Now bitTimes have the number of retries (us *2) // that were needed to find the end of each data bit // Spec: 0 is 26 to 28 us // Spec: 1 is 70 us // bitTimes[x] <= 14 is a 0 (14x2us = 28us) // bitTimes[x] > 15 is a 1 (15x2us = 30us) // Note: the bits are offset by one from the data sheet, not sure why currentHumidity = 0; currentTemperature = 0; checkSum = 0; // First 16 bit is Humidity for (i=0; i<16; i++) { if (bitTimes[i] > 14) { currentHumidity |= ( 1 << (15-i)); } } // Second 16 bit is Temperature for (i=0; i<16; i ++) { if (bitTimes[i+16] > 14) { currentTemperature |= (1 <<(15-i)); } } // Last 8 bit is Checksum for (i=0; i<8; i++) { if (bitTimes[i+32] > 14) { 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; return DHT_ERROR_NONE; } return DHT_ERROR_CHECKSUM; } float DHT22::getTemperatureC() { return _lastTemperature; } float DHT22::getHumidity() { return _lastHumidity; }