dht library
Fork of DHT by
Diff: DHT.cpp
- Revision:
- 1:a2bc4effa732
- Parent:
- 0:9b5b3200688f
--- a/DHT.cpp Mon Jul 09 19:47:43 2012 +0000 +++ b/DHT.cpp Sat May 13 16:27:52 2017 +0000 @@ -9,7 +9,7 @@ * * Copyright (C) Wim De Roeve * based on DHT22 sensor library by HO WING KIT - * Arduino DHT11 library + * 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 @@ -29,127 +29,114 @@ * 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) { + +#define DHT_DATA_BIT_COUNT 40 + +DHT::DHT(PinName pin, eType DHTtype) +{ _pin = pin; _DHTtype = DHTtype; - _firsttime=true; + _firsttime = true; } - -DHT::~DHT() { + +DHT::~DHT() +{ + } - -int DHT::readData() { - int i, j, retryCount,b; - unsigned int bitTimes[DHT_DATA_BIT_COUNT]; - + +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); - - for (i = 0; i < DHT_DATA_BIT_COUNT; i++) { - bitTimes[i] = 0; + + // IO must be in hi state to start + if (ERROR_NONE != stall(DHT_io, 0, 250)) { + return BUS_BUSY; } - - 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)); - - + + // start the transfer DHT_io.output(); DHT_io = 0; wait_ms(18); DHT_io = 1; - wait_us(40); + wait_us(30); 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 till the sensor grabs the bus + if (ERROR_NONE != stall(DHT_io, 1, 100)) { + return ERROR_NOT_PRESENT; } - - wait_us(80); - + // 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++) { - - retryCount = 0; - do { - if (retryCount > 75) { - err = ERROR_DATA_TIMEOUT; - return err; - } - retryCount++; - wait_us(1); - } while (DHT_io == 0); + if (ERROR_NONE != stall(DHT_io, 0, 75)) { + return ERROR_DATA_TIMEOUT; + } + // logic 0 is 28us max, 1 is 70us wait_us(40); - bitTimes[i*8+j]=DHT_io; - - int count = 0; - while (DHT_io == 1 && count < 100) { - wait_us(1); - count++; + bit_value[i*8+j] = DHT_io; + if (ERROR_NONE != stall(DHT_io, 1, 50)) { + return ERROR_DATA_TIMEOUT; } } } - DHT_io.output(); - DHT_io = 1; + // store the data 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)); + if (bit_value[i*8+j] == 1) { + 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)) { + + // 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(); - + _lastTemperature = CalcTemperature(); + _lastHumidity = CalcHumidity(); + } else { err = ERROR_CHECKSUM; } - + return err; - + } - -float DHT::CalcTemperature() { + +float DHT::CalcTemperature() +{ int v; - + switch (_DHTtype) { case DHT11: v = DHT_data[2]; @@ -165,46 +152,51 @@ } return 0; } - -float DHT::ReadHumidity() { + +float DHT::ReadHumidity() +{ return _lastHumidity; } - -float DHT::ConvertCelciustoFarenheit(float celsius) { + +float DHT::ConvertCelciustoFarenheit(float const celsius) +{ return celsius * 9 / 5 + 32; } - -float DHT::ConvertCelciustoKelvin(float celsius) { - return celsius + 273.15; + +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 celsius, float humidity) { - float A0= 373.15/(273.15 + celsius); +float DHT::CalcdewPoint(float const celsius, float const humidity) +{ + float A0= 373.15f/(273.15f + 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 += 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/0.61078); // temp var - return (241.88 * T) / (17.558-T); + 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 celsius, float humidity) +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 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) { + +float DHT::ReadTemperature(eScale Scale) +{ if (Scale == FARENHEIT) return ConvertCelciustoFarenheit(_lastTemperature); else if (Scale == KELVIN) @@ -212,10 +204,11 @@ else return _lastTemperature; } - -float DHT::CalcHumidity() { + +float DHT::CalcHumidity() +{ int v; - + switch (_DHTtype) { case DHT11: v = DHT_data[0];