mirror of
https://github.com/adafruit/DHT-sensor-library.git
synced 2023-10-23 22:20:38 +03:00
documented DHT
This commit is contained in:
Jan Hoffmann
264
DHT.cpp
264
DHT.cpp
@@ -1,29 +1,62 @@
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/* DHT library
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MIT license
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written by Adafruit Industries
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*/
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/*!
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* @file DHT.cpp
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*
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* @mainpage DHT series of low cost temperature/humidity sensors.
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*
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* @section intro_sec Introduction
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*
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* This is a library for DHT series of low cost temperature/humidity sensors.
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*
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* You must have Adafruit Unified Sensor Library library installed to use this
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* class.
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*
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* Adafruit invests time and resources providing this open source code,
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* please support Adafruit andopen-source hardware by purchasing products
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* from Adafruit!
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*
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* @section author Author
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*
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* Written by Adafruit Industries.
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*
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* @section license License
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*
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* MIT license, all text above must be included in any redistribution
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*/
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#include "DHT.h"
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#define MIN_INTERVAL 2000
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#define TIMEOUT -1
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#define MIN_INTERVAL 2000 /**< min interval value */
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#define TIMEOUT -1 /**< timeout on */
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/*!
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* @brief Instantiates a new DHT class
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* @param pin
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* pin number that sensor is connected
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* @param type
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* type of sensor
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* @param count
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* number of sensors
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*/
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DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
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_pin = pin;
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_type = type;
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#ifdef __AVR
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_bit = digitalPinToBitMask(pin);
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_port = digitalPinToPort(pin);
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#endif
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_maxcycles = microsecondsToClockCycles(1000); // 1 millisecond timeout for
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// reading pulses from DHT sensor.
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#ifdef __AVR
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_bit = digitalPinToBitMask(pin);
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_port = digitalPinToPort(pin);
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#endif
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_maxcycles =
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microsecondsToClockCycles(1000); // 1 millisecond timeout for
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// reading pulses from DHT sensor.
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// Note that count is now ignored as the DHT reading algorithm adjusts itself
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// based on the speed of the processor.
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}
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// Optionally pass pull-up time (in microseconds) before DHT reading starts.
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// Default is 55 (see function declaration in DHT.h).
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/*!
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* @brief Setup sensor pins and set pull timings
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* @param usec
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* Optionally pass pull-up time (in microseconds) before DHT reading
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*starts. Default is 55 (see function declaration in DHT.h).
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*/
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void DHT::begin(uint8_t usec) {
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// set up the pins!
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pinMode(_pin, INPUT_PULLUP);
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@@ -31,11 +64,21 @@ void DHT::begin(uint8_t usec) {
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// >= MIN_INTERVAL right away. Note that this assignment wraps around,
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// but so will the subtraction.
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_lastreadtime = millis() - MIN_INTERVAL;
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DEBUG_PRINT("DHT max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC);
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DEBUG_PRINT("DHT max clock cycles: ");
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DEBUG_PRINTLN(_maxcycles, DEC);
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pullTime = usec;
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}
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//boolean S == Scale. True == Fahrenheit; False == Celcius
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/*!
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* @brief Read temperature
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* @param S
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* Scale. Boolean value:
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* - true = Fahrenheit
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* - false = Celcius
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* @param force
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* true if in force mode
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* @return Temperature value in selected scale
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*/
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float DHT::readTemperature(bool S, bool force) {
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float f = NAN;
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@@ -44,10 +87,10 @@ float DHT::readTemperature(bool S, bool force) {
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case DHT11:
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f = data[2];
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if (data[3] & 0x80) {
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f = -1 - f ;
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f = -1 - f;
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}
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f += (data[3] & 0x0f) * 0.1;
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if(S) {
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if (S) {
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f = convertCtoF(f);
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}
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break;
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@@ -57,7 +100,7 @@ float DHT::readTemperature(bool S, bool force) {
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if (data[2] & 0x80) {
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f *= -1;
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}
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if(S) {
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if (S) {
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f = convertCtoF(f);
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}
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break;
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@@ -68,7 +111,7 @@ float DHT::readTemperature(bool S, bool force) {
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if (data[2] & 0x80) {
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f *= -1;
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}
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if(S) {
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if (S) {
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f = convertCtoF(f);
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}
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break;
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@@ -77,14 +120,28 @@ float DHT::readTemperature(bool S, bool force) {
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return f;
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}
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float DHT::convertCtoF(float c) {
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return c * 1.8 + 32;
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}
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/*!
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* @brief Converts Celcius to Fahrenheit
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* @param c
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* value in Celcius
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* @return float value in Fahrenheit
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*/
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float DHT::convertCtoF(float c) { return c * 1.8 + 32; }
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float DHT::convertFtoC(float f) {
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return (f - 32) * 0.55555;
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}
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/*!
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* @brief Converts Fahrenheit to Celcius
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* @param f
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* value in Fahrenheit
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* @return float value in Celcius
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*/
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float DHT::convertFtoC(float f) { return (f - 32) * 0.55555; }
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/*!
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* @brief Read Humidity
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* @param force
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* force read mode
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* @return float value - humidity in percent
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*/
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float DHT::readHumidity(bool force) {
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float f = NAN;
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if (read(force)) {
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@@ -103,46 +160,71 @@ float DHT::readHumidity(bool force) {
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return f;
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}
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//boolean isFahrenheit: True == Fahrenheit; False == Celcius
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/*!
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* @brief Compute Heat Index
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* Simplified version that reads temp and humidity from sensor
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* @param isFahrenheit
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* true if fahrenheit, false if celcius (default
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*true)
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* @return float heat index
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*/
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float DHT::computeHeatIndex(bool isFahrenheit) {
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float hi = computeHeatIndex(readTemperature(isFahrenheit), readHumidity(),
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isFahrenheit);
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isFahrenheit);
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return hi;
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}
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//boolean isFahrenheit: True == Fahrenheit; False == Celcius
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/*!
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* @brief Compute Heat Index
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* Using both Rothfusz and Steadman's equations
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* (http://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml)
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* @param temperature
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* temperature in selected scale
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* @param percentHumidity
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* humidity in percent
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* @param isFahrenheit
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* true if fahrenheit, false if celcius
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* @return float heat index
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*/
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float DHT::computeHeatIndex(float temperature, float percentHumidity,
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bool isFahrenheit) {
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// Using both Rothfusz and Steadman's equations
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// http://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml
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bool isFahrenheit) {
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float hi;
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if (!isFahrenheit)
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temperature = convertCtoF(temperature);
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hi = 0.5 * (temperature + 61.0 + ((temperature - 68.0) * 1.2) + (percentHumidity * 0.094));
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hi = 0.5 * (temperature + 61.0 + ((temperature - 68.0) * 1.2) +
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(percentHumidity * 0.094));
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if (hi > 79) {
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hi = -42.379 +
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2.04901523 * temperature +
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10.14333127 * percentHumidity +
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-0.22475541 * temperature*percentHumidity +
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-0.00683783 * pow(temperature, 2) +
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-0.05481717 * pow(percentHumidity, 2) +
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0.00122874 * pow(temperature, 2) * percentHumidity +
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0.00085282 * temperature*pow(percentHumidity, 2) +
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-0.00000199 * pow(temperature, 2) * pow(percentHumidity, 2);
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hi = -42.379 + 2.04901523 * temperature + 10.14333127 * percentHumidity +
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-0.22475541 * temperature * percentHumidity +
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-0.00683783 * pow(temperature, 2) +
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-0.05481717 * pow(percentHumidity, 2) +
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0.00122874 * pow(temperature, 2) * percentHumidity +
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0.00085282 * temperature * pow(percentHumidity, 2) +
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-0.00000199 * pow(temperature, 2) * pow(percentHumidity, 2);
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if((percentHumidity < 13) && (temperature >= 80.0) && (temperature <= 112.0))
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hi -= ((13.0 - percentHumidity) * 0.25) * sqrt((17.0 - abs(temperature - 95.0)) * 0.05882);
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if ((percentHumidity < 13) && (temperature >= 80.0) &&
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(temperature <= 112.0))
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hi -= ((13.0 - percentHumidity) * 0.25) *
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sqrt((17.0 - abs(temperature - 95.0)) * 0.05882);
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else if((percentHumidity > 85.0) && (temperature >= 80.0) && (temperature <= 87.0))
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else if ((percentHumidity > 85.0) && (temperature >= 80.0) &&
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(temperature <= 87.0))
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hi += ((percentHumidity - 85.0) * 0.1) * ((87.0 - temperature) * 0.2);
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}
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return isFahrenheit ? hi : convertFtoC(hi);
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}
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/*!
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* @brief Read value from sensor or return last one from less than two
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*seconds.
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* @param force
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* true if using force mode
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* @return float value
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*/
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bool DHT::read(bool force) {
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// Check if sensor was read less than two seconds ago and return early
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// to use last reading.
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@@ -156,7 +238,7 @@ bool DHT::read(bool force) {
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data[0] = data[1] = data[2] = data[3] = data[4] = 0;
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#if defined(ESP8266)
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yield(); // Handle WiFi / reset software watchdog
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yield(); // Handle WiFi / reset software watchdog
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#endif
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// Send start signal. See DHT datasheet for full signal diagram:
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@@ -170,15 +252,15 @@ bool DHT::read(bool force) {
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// First set data line low for a period according to sensor type
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pinMode(_pin, OUTPUT);
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digitalWrite(_pin, LOW);
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switch(_type) {
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case DHT22:
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case DHT21:
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delayMicroseconds(1100); // data sheet says "at least 1ms"
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break;
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case DHT11:
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default:
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delay(20); //data sheet says at least 18ms, 20ms just to be safe
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break;
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switch (_type) {
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case DHT22:
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case DHT21:
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delayMicroseconds(1100); // data sheet says "at least 1ms"
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break;
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case DHT11:
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default:
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delay(20); // data sheet says at least 18ms, 20ms just to be safe
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break;
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}
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uint32_t cycles[80];
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@@ -214,29 +296,29 @@ bool DHT::read(bool force) {
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// then it's a 1. We measure the cycle count of the initial 50us low pulse
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// and use that to compare to the cycle count of the high pulse to determine
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// if the bit is a 0 (high state cycle count < low state cycle count), or a
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// 1 (high state cycle count > low state cycle count). Note that for speed all
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// the pulses are read into a array and then examined in a later step.
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for (int i=0; i<80; i+=2) {
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cycles[i] = expectPulse(LOW);
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cycles[i+1] = expectPulse(HIGH);
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// 1 (high state cycle count > low state cycle count). Note that for speed
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// all the pulses are read into a array and then examined in a later step.
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for (int i = 0; i < 80; i += 2) {
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cycles[i] = expectPulse(LOW);
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cycles[i + 1] = expectPulse(HIGH);
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}
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} // Timing critical code is now complete.
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// Inspect pulses and determine which ones are 0 (high state cycle count < low
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// state cycle count), or 1 (high state cycle count > low state cycle count).
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for (int i=0; i<40; ++i) {
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uint32_t lowCycles = cycles[2*i];
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uint32_t highCycles = cycles[2*i+1];
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for (int i = 0; i < 40; ++i) {
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uint32_t lowCycles = cycles[2 * i];
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uint32_t highCycles = cycles[2 * i + 1];
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if ((lowCycles == TIMEOUT) || (highCycles == TIMEOUT)) {
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DEBUG_PRINTLN(F("DHT timeout waiting for pulse."));
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_lastresult = false;
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return _lastresult;
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}
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data[i/8] <<= 1;
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data[i / 8] <<= 1;
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// Now compare the low and high cycle times to see if the bit is a 0 or 1.
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if (highCycles > lowCycles) {
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// High cycles are greater than 50us low cycle count, must be a 1.
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data[i/8] |= 1;
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data[i / 8] |= 1;
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}
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// Else high cycles are less than (or equal to, a weird case) the 50us low
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// cycle count so this must be a zero. Nothing needs to be changed in the
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@@ -244,19 +326,23 @@ bool DHT::read(bool force) {
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}
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DEBUG_PRINTLN(F("Received from DHT:"));
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DEBUG_PRINT(data[0], HEX); DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[1], HEX); DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[2], HEX); DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[3], HEX); DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[4], HEX); DEBUG_PRINT(F(" =? "));
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DEBUG_PRINT(data[0], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[1], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[2], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[3], HEX);
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DEBUG_PRINT(F(", "));
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DEBUG_PRINT(data[4], HEX);
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DEBUG_PRINT(F(" =? "));
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DEBUG_PRINTLN((data[0] + data[1] + data[2] + data[3]) & 0xFF, HEX);
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// Check we read 40 bits and that the checksum matches.
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if (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
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_lastresult = true;
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return _lastresult;
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}
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else {
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} else {
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DEBUG_PRINTLN(F("DHT checksum failure!"));
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_lastresult = false;
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return _lastresult;
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@@ -276,24 +362,24 @@ uint32_t DHT::expectPulse(bool level) {
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#else
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uint16_t count = 0; // To work fast enough on slower AVR boards
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#endif
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// On AVR platforms use direct GPIO port access as it's much faster and better
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// for catching pulses that are 10's of microseconds in length:
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#ifdef __AVR
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uint8_t portState = level ? _bit : 0;
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while ((*portInputRegister(_port) & _bit) == portState) {
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if (count++ >= _maxcycles) {
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return TIMEOUT; // Exceeded timeout, fail.
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}
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// On AVR platforms use direct GPIO port access as it's much faster and better
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// for catching pulses that are 10's of microseconds in length:
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#ifdef __AVR
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uint8_t portState = level ? _bit : 0;
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while ((*portInputRegister(_port) & _bit) == portState) {
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if (count++ >= _maxcycles) {
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return TIMEOUT; // Exceeded timeout, fail.
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}
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// Otherwise fall back to using digitalRead (this seems to be necessary on ESP8266
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// right now, perhaps bugs in direct port access functions?).
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#else
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while (digitalRead(_pin) == level) {
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if (count++ >= _maxcycles) {
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return TIMEOUT; // Exceeded timeout, fail.
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}
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}
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// Otherwise fall back to using digitalRead (this seems to be necessary on
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// ESP8266 right now, perhaps bugs in direct port access functions?).
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#else
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while (digitalRead(_pin) == level) {
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if (count++ >= _maxcycles) {
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return TIMEOUT; // Exceeded timeout, fail.
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}
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#endif
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}
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#endif
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return count;
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}
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