Temp and Humidity sensor device driver.
Dependents: temp_hum IAC_send Smart_Home_sensors
Fork of DHT by
DHT.cpp
- Committer:
- sam_grove
- Date:
- 2016-05-28
- Revision:
- 4:6937e130feca
- Parent:
- 2:df22ddf10d75
File content as of revision 4:6937e130feca:
/* * 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 40 DHT::DHT(PinName pin, eType DHTtype) { _pin = pin; _DHTtype = DHTtype; _firsttime = true; } DHT::~DHT() { } eError DHT::stall(DigitalInOut &io, int const level, int const max_time) { int cnt = 0; while (level == io) { if (cnt > max_time) { return ERROR_NO_PATIENCE; } cnt++; wait_us(1); } return ERROR_NONE; } eError DHT::readData() { uint8_t i = 0, j = 0, b = 0, data_valid = 0; uint32_t bit_value[DHT_DATA_BIT_COUNT] = {0}; eError err = ERROR_NONE; time_t currentTime = time(NULL); DigitalInOut DHT_io(_pin); // IO must be in hi state to start if (ERROR_NONE != stall(DHT_io, 0, 250)) { return BUS_BUSY; } // start the transfer DHT_io.output(); DHT_io = 0; wait_ms(18); DHT_io = 1; wait_us(30); DHT_io.input(); // wait till the sensor grabs the bus if (ERROR_NONE != stall(DHT_io, 1, 100)) { return ERROR_NOT_PRESENT; } // sensor should signal low 80us and then hi 80us if (ERROR_NONE != stall(DHT_io, 0, 100)) { return ERROR_SYNC_TIMEOUT; } if (ERROR_NONE != stall(DHT_io, 1, 100)) { return ERROR_NO_PATIENCE; } // capture the data for (i = 0; i < 5; i++) { for (j = 0; j < 8; j++) { if (ERROR_NONE != stall(DHT_io, 0, 75)) { return ERROR_DATA_TIMEOUT; } // logic 0 is 28us max, 1 is 70us wait_us(40); bit_value[i*8+j] = DHT_io; if (ERROR_NONE != stall(DHT_io, 1, 50)) { return ERROR_DATA_TIMEOUT; } } } // store the data for (i = 0; i < 5; i++) { b=0; for (j=0; j<8; j++) { if (bit_value[i*8+j] == 1) { b |= (1 << (7-j)); } } DHT_data[i]=b; } // uncomment to see the checksum error if it exists //printf(" 0x%02x + 0x%02x + 0x%02x + 0x%02x = 0x%02x \n", DHT_data[0], DHT_data[1], DHT_data[2], DHT_data[3], DHT_data[4]); data_valid = DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3]; if (DHT_data[4] == data_valid) { _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 const celsius) { return celsius * 9 / 5 + 32; } float DHT::ConvertCelciustoKelvin(float const celsius) { return celsius + 273.15f; } // dewPoint function NOAA // reference: http://wahiduddin.net/calc/density_algorithms.htm float DHT::CalcdewPoint(float const celsius, float const humidity) { float A0= 373.15f/(273.15f + celsius); float SUM = -7.90298 * (A0-1); SUM += 5.02808f * log10(A0); SUM += -1.3816e-7 * (pow(10, (11.344f*(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/0.61078f); // temp var return (241.88f * T) / (17.558f-T); } // delta max = 0.6544 wrt dewPoint() // 5x faster than dewPoint() // reference: http://en.wikipedia.org/wiki/Dew_point float DHT::CalcdewPointFast(float const celsius, float const 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; }