Fork of DHT repo with checksum fixes.
Fork of DHT by
DHT.cpp
- Committer:
- Wimpie
- Date:
- 2012-07-09
- Revision:
- 0:9b5b3200688f
- Child:
- 1:932d451474dc
File content as of revision 0:9b5b3200688f:
/* * DHT Library for Digital-output Humidity and Temperature sensors * * Works with DHT11, DHT22 * SEN11301P, Grove - Temperature&Humidity Sensor (Seeed Studio) * SEN51035P, Grove - Temperature&Humidity Sensor Pro (Seeed Studio) * AM2302 , temperature-humidity sensor * HM2303 , Digital-output humidity and temperature sensor * * Copyright (C) Wim De Roeve * based on DHT22 sensor library by HO WING KIT * Arduino DHT11 library * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documnetation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS OR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ #include "DHT.h" #define DHT_DATA_BIT_COUNT 41 DHT::DHT(PinName pin,int DHTtype) { _pin = pin; _DHTtype = DHTtype; _firsttime=true; } DHT::~DHT() { } int DHT::readData() { int i, j, retryCount,b; unsigned int bitTimes[DHT_DATA_BIT_COUNT]; eError err = ERROR_NONE; time_t currentTime = time(NULL); DigitalInOut DHT_io(_pin); for (i = 0; i < DHT_DATA_BIT_COUNT; i++) { bitTimes[i] = 0; } if (!_firsttime) { if (int(currentTime - _lastReadTime) < 2) { err = ERROR_NO_PATIENCE; return err; } } else { _firsttime=false; _lastReadTime=currentTime; } retryCount = 0; do { if (retryCount > 125) { err = BUS_BUSY; return err; } retryCount ++; wait_us(2); } while ((DHT_io==0)); DHT_io.output(); DHT_io = 0; wait_ms(18); DHT_io = 1; wait_us(40); DHT_io.input(); retryCount = 0; do { if (retryCount > 40) { err = ERROR_NOT_PRESENT; return err; } retryCount++; wait_us(1); } while ((DHT_io==1)); if (err != ERROR_NONE) { return err; } wait_us(80); for (i = 0; i < 5; i++) { for (j = 0; j < 8; j++) { retryCount = 0; do { if (retryCount > 75) { err = ERROR_DATA_TIMEOUT; return err; } retryCount++; wait_us(1); } while (DHT_io == 0); wait_us(40); bitTimes[i*8+j]=DHT_io; int count = 0; while (DHT_io == 1 && count < 100) { wait_us(1); count++; } } } DHT_io.output(); DHT_io = 1; for (i = 0; i < 5; i++) { b=0; for (j=0; j<8; j++) { if (bitTimes[i*8+j+1] > 0) { b |= ( 1 << (7-j)); } } DHT_data[i]=b; } if (DHT_data[4] == ((DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3]) & 0xFF)) { _lastReadTime = currentTime; _lastTemperature=CalcTemperature(); _lastHumidity=CalcHumidity(); } else { err = ERROR_CHECKSUM; } return err; } float DHT::CalcTemperature() { int v; switch (_DHTtype) { case DHT11: v = DHT_data[2]; return float(v); case DHT22: v = DHT_data[2] & 0x7F; v *= 256; v += DHT_data[3]; v /= 10; if (DHT_data[2] & 0x80) v *= -1; return float(v); } return 0; } float DHT::ReadHumidity() { return _lastHumidity; } float DHT::ConvertCelciustoFarenheit(float celsius) { return celsius * 9 / 5 + 32; } float DHT::ConvertCelciustoKelvin(float celsius) { return celsius + 273.15; } // dewPoint function NOAA // reference: http://wahiduddin.net/calc/density_algorithms.htm float DHT::CalcdewPoint(float celsius, float humidity) { float A0= 373.15/(273.15 + celsius); float SUM = -7.90298 * (A0-1); SUM += 5.02808 * log10(A0); SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ; SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ; SUM += log10(1013.246); float VP = pow(10, SUM-3) * humidity; float T = log(VP/0.61078); // temp var return (241.88 * T) / (17.558-T); } // delta max = 0.6544 wrt dewPoint() // 5x faster than dewPoint() // reference: http://en.wikipedia.org/wiki/Dew_point float DHT::CalcdewPointFast(float celsius, float humidity) { float a = 17.271; float b = 237.7; float temp = (a * celsius) / (b + celsius) + log(humidity/100); float Td = (b * temp) / (a - temp); return Td; } float DHT::ReadTemperature(eScale Scale) { if (Scale == FARENHEIT) return ConvertCelciustoFarenheit(_lastTemperature); else if (Scale == KELVIN) return ConvertCelciustoKelvin(_lastTemperature); else return _lastTemperature; } float DHT::CalcHumidity() { int v; switch (_DHTtype) { case DHT11: v = DHT_data[0]; return float(v); case DHT22: v = DHT_data[0]; v *= 256; v += DHT_data[1]; v /= 10; return float(v); } return 0; }