260 lines
8.4 KiB
C++
260 lines
8.4 KiB
C++
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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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#include "DHT.h"
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#define MIN_INTERVAL 2000
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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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// Note that count is now ignored as the DHT reading algorithm adjusts itself
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// basd on the speed of the processor.
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}
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void DHT::begin(void) {
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// set up the pins!
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pinMode(_pin, INPUT_PULLUP);
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// Using this value makes sure that millis() - lastreadtime will be
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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 = -MIN_INTERVAL;
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DEBUG_PRINT("Max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC);
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}
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//boolean S == Scale. True == Fahrenheit; False == Celcius
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float DHT::readTemperature(bool S, bool force) {
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float f = NAN;
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if (read(force)) {
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switch (_type) {
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case DHT11:
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f = data[2];
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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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case DHT22:
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case DHT21:
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f = data[2] & 0x7F;
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f *= 256;
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f += data[3];
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f *= 0.1;
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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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f = convertCtoF(f);
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}
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break;
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}
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}
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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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float DHT::convertFtoC(float f) {
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return (f - 32) * 0.55555;
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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()) {
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switch (_type) {
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case DHT11:
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f = data[0];
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break;
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case DHT22:
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case DHT21:
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f = data[0];
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f *= 256;
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f += data[1];
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f *= 0.1;
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break;
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}
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}
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return f;
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}
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//boolean isFahrenheit: True == Fahrenheit; False == Celcius
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float DHT::computeHeatIndex(float temperature, float percentHumidity, 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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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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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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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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else if((percentHumidity > 85.0) && (temperature >= 80.0) && (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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boolean 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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uint32_t currenttime = millis();
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if (!force && ((currenttime - _lastreadtime) < 2000)) {
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return _lastresult; // return last correct measurement
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}
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_lastreadtime = currenttime;
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// Reset 40 bits of received data to zero.
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data[0] = data[1] = data[2] = data[3] = data[4] = 0;
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// Send start signal. See DHT datasheet for full signal diagram:
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// http://www.adafruit.com/datasheets/Digital%20humidity%20and%20temperature%20sensor%20AM2302.pdf
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// Go into high impedence state to let pull-up raise data line level and
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// start the reading process.
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digitalWrite(_pin, HIGH);
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delay(250);
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// First set data line low for 20 milliseconds.
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pinMode(_pin, OUTPUT);
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digitalWrite(_pin, LOW);
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delay(20);
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uint32_t cycles[80];
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{
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// Turn off interrupts temporarily because the next sections are timing critical
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// and we don't want any interruptions.
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InterruptLock lock;
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// End the start signal by setting data line high for 40 microseconds.
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digitalWrite(_pin, HIGH);
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delayMicroseconds(40);
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// Now start reading the data line to get the value from the DHT sensor.
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pinMode(_pin, INPUT_PULLUP);
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delayMicroseconds(10); // Delay a bit to let sensor pull data line low.
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// First expect a low signal for ~80 microseconds followed by a high signal
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// for ~80 microseconds again.
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if (expectPulse(LOW) == 0) {
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DEBUG_PRINTLN(F("Timeout waiting for start signal low pulse."));
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_lastresult = false;
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return _lastresult;
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}
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if (expectPulse(HIGH) == 0) {
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DEBUG_PRINTLN(F("Timeout waiting for start signal high pulse."));
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_lastresult = false;
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return _lastresult;
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}
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// Now read the 40 bits sent by the sensor. Each bit is sent as a 50
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// microsecond low pulse followed by a variable length high pulse. If the
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// high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds
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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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}
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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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if ((lowCycles == 0) || (highCycles == 0)) {
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DEBUG_PRINTLN(F("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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// 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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}
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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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// stored data.
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}
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DEBUG_PRINTLN(F("Received:"));
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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_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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DEBUG_PRINTLN(F("Checksum failure!"));
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_lastresult = false;
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return _lastresult;
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}
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}
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// Expect the signal line to be at the specified level for a period of time and
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// return a count of loop cycles spent at that level (this cycle count can be
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// used to compare the relative time of two pulses). If more than a millisecond
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// ellapses without the level changing then the call fails with a 0 response.
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// This is adapted from Arduino's pulseInLong function (which is only available
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// in the very latest IDE versions):
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// https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/wiring_pulse.c
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uint32_t DHT::expectPulse(bool level) {
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uint32_t count = 0;
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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 0; // 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 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 0; // Exceeded timeout, fail.
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}
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}
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#endif
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return count;
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}
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