Fix merge conflict with interrupt disable lock.

Cause interrupts to be reenabled if a timeout occurs while waiting for the sensor

DHT.cpp

@@ -9,8 +9,13 @@ written by Adafruit Industries
 DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
   _pin = pin;
   _type = type;
-  _count = count;
-  firstreading = true;
+  _firstreading = true;
+  _bit = digitalPinToBitMask(pin);
+  _port = digitalPinToPort(pin);
+  _maxcycles = microsecondsToClockCycles(1000);  // 1 millisecond timeout for
+                                                 // reading pulses from DHT sensor.
+  // Note that count is now ignored as the DHT reading algorithm adjusts itself
+  // basd on the speed of the processor.
 }
 
 void DHT::begin(void) {
@@ -18,36 +23,38 @@ void DHT::begin(void) {
   pinMode(_pin, INPUT);
   digitalWrite(_pin, HIGH);
   _lastreadtime = 0;
+  DEBUG_PRINT("Max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC);
 }
 
-//boolean S == Scale.  True == Farenheit; False == Celcius
+//boolean S == Scale.  True == Fahrenheit; False == Celcius
 float DHT::readTemperature(bool S) {
-  float f;
+  float f = NAN;
 
   if (read()) {
     switch (_type) {
     case DHT11:
       f = data[2];
-      if(S)
+      if(S) {
         f = convertCtoF(f);
-      	
-      return f;
+      }
+      break;
     case DHT22:
     case DHT21:
       f = data[2] & 0x7F;
       f *= 256;
       f += data[3];
       f /= 10;
-      if (data[2] & 0x80)
+      if (data[2] & 0x80) {
         f *= -1;
-      if(S)
+      }
+      if(S) {
         f = convertCtoF(f);
-
+      }
+      break;
+    }
+  }
   return f;
 }
-  }
-  return NAN;
-}
 
 float DHT::convertCtoF(float c) {
   return c * 9 / 5 + 32;
@@ -58,122 +65,193 @@ float DHT::convertFtoC(float f) {
 }
 
 float DHT::readHumidity(void) {
-  float f;
+  float f = NAN;
   if (read()) {
     switch (_type) {
     case DHT11:
       f = data[0];
-      return f;
+      break;
     case DHT22:
     case DHT21:
       f = data[0];
       f *= 256;
       f += data[1];
       f /= 10;
+      break;
+    }
+  }
   return f;
 }
-  }
-  return NAN;
-}
 
-float DHT::computeHeatIndex(float tempFahrenheit, float percentHumidity) {
+//boolean isFahrenheit: True == Fahrenheit; False == Celcius
+float DHT::computeHeatIndex(float temperature, float percentHumidity, bool isFahrenheit) {
   // Adapted from equation at: https://github.com/adafruit/DHT-sensor-library/issues/9 and
   // Wikipedia: http://en.wikipedia.org/wiki/Heat_index
+  if (!isFahrenheit) {
+    // Celsius heat index calculation.
+    return -8.784695 +
+             1.61139411 * temperature +
+             2.338549   * percentHumidity +
+            -0.14611605 * temperature*percentHumidity +
+            -0.01230809 * pow(temperature, 2) +
+            -0.01642482 * pow(percentHumidity, 2) +
+             0.00221173 * pow(temperature, 2) * percentHumidity +
+             0.00072546 * temperature*pow(percentHumidity, 2) +
+            -0.00000358 * pow(temperature, 2) * pow(percentHumidity, 2);
+  }
+  else {
+    // Fahrenheit heat index calculation.
     return -42.379 +
-           2.04901523 * tempFahrenheit + 
+             2.04901523 * temperature +
             10.14333127 * percentHumidity +
-          -0.22475541 * tempFahrenheit*percentHumidity +
-          -0.00683783 * pow(tempFahrenheit, 2) +
+            -0.22475541 * temperature*percentHumidity +
+            -0.00683783 * pow(temperature, 2) +
             -0.05481717 * pow(percentHumidity, 2) +
-           0.00122874 * pow(tempFahrenheit, 2) * percentHumidity + 
-           0.00085282 * tempFahrenheit*pow(percentHumidity, 2) +
-          -0.00000199 * pow(tempFahrenheit, 2) * pow(percentHumidity, 2);
+             0.00122874 * pow(temperature, 2) * percentHumidity +
+             0.00085282 * temperature*pow(percentHumidity, 2) +
+            -0.00000199 * pow(temperature, 2) * pow(percentHumidity, 2);
+  }
 }
 
-
 boolean DHT::read(void) {
-  uint8_t laststate = HIGH;
-  uint8_t counter = 0;
-  uint8_t j = 0, i;
-  unsigned long currenttime;
-
   // Check if sensor was read less than two seconds ago and return early
   // to use last reading.
-  currenttime = millis();
+  uint32_t currenttime = millis();
   if (currenttime < _lastreadtime) {
     // ie there was a rollover
     _lastreadtime = 0;
   }
-  if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
-    return true; // return last correct measurement
-    //delay(2000 - (currenttime - _lastreadtime));
+  if (!_firstreading && ((currenttime - _lastreadtime) < 2000)) {
+    return _lastresult; // return last correct measurement
   }
-  firstreading = false;
-  /*
-    Serial.print("Currtime: "); Serial.print(currenttime);
-    Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
-  */
+  _firstreading = false;
   _lastreadtime = millis();
 
+  // Reset 40 bits of received data to zero.
   data[0] = data[1] = data[2] = data[3] = data[4] = 0;
 
-  // pull the pin high and wait 250 milliseconds
+  // Send start signal.  See DHT datasheet for full signal diagram:
+  //   http://www.adafruit.com/datasheets/Digital%20humidity%20and%20temperature%20sensor%20AM2302.pdf
+
+  // Go into high impedence state to let pull-up raise data line level and
+  // start the reading process.
   digitalWrite(_pin, HIGH);
   delay(250);
 
-  // now pull it low for ~20 milliseconds
+  // First set data line low for 20 milliseconds.
   pinMode(_pin, OUTPUT);
   digitalWrite(_pin, LOW);
   delay(20);
-  noInterrupts();
+
+  uint32_t cycles[80];
+  {
+    // Turn off interrupts temporarily because the next sections are timing critical
+    // and we don't want any interruptions.
+    InterruptLock lock;
+
+    // End the start signal by setting data line high for 40 microseconds.
     digitalWrite(_pin, HIGH);
     delayMicroseconds(40);
+
+    // Now start reading the data line to get the value from the DHT sensor.
     pinMode(_pin, INPUT);
+    delayMicroseconds(10);  // Delay a bit to let sensor pull data line low.
 
-  // read in timings
-  for ( i=0; i< MAXTIMINGS; i++) {
-    counter = 0;
-    while (digitalRead(_pin) == laststate) {
-      counter++;
-      delayMicroseconds(1);
-      if (counter == 255) {
-        break;
+    // First expect a low signal for ~80 microseconds followed by a high signal
+    // for ~80 microseconds again.
+    if (expectPulse(LOW) == 0) {
+      DEBUG_PRINTLN(F("Timeout waiting for start signal low pulse."));
+      _lastresult = false;
+      return _lastresult;
     }
-    }
-    laststate = digitalRead(_pin);
-
-    if (counter == 255) break;
-
-    // ignore first 3 transitions
-    if ((i >= 4) && (i%2 == 0)) {
-      // shove each bit into the storage bytes
-      data[j/8] <<= 1;
-      if (counter > _count)
-        data[j/8] |= 1;
-      j++;
+    if (expectPulse(HIGH) == 0) {
+      DEBUG_PRINTLN(F("Timeout waiting for start signal high pulse."));
+      _lastresult = false;
+      return _lastresult;
     }
 
+    // Now read the 40 bits sent by the sensor.  Each bit is sent as a 50
+    // microsecond low pulse followed by a variable length high pulse.  If the
+    // high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds
+    // then it's a 1.  We measure the cycle count of the initial 50us low pulse
+    // and use that to compare to the cycle count of the high pulse to determine
+    // if the bit is a 0 (high state cycle count < low state cycle count), or a
+    // 1 (high state cycle count > low state cycle count). Note that for speed all
+    // the pulses are read into a array and then examined in a later step.
+    for (int i=0; i<80; i+=2) {
+      cycles[i]   = expectPulse(LOW);
+      cycles[i+1] = expectPulse(HIGH);
+    }
+  } // Timing critical code is now complete.
+
+  // Inspect pulses and determine which ones are 0 (high state cycle count < low
+  // state cycle count), or 1 (high state cycle count > low state cycle count).
+  for (int i=0; i<40; ++i) {
+    uint32_t lowCycles  = cycles[2*i];
+    uint32_t highCycles = cycles[2*i+1];
+    if ((lowCycles == 0) || (highCycles == 0)) {
+      DEBUG_PRINTLN(F("Timeout waiting for pulse."));
+      _lastresult = false;
+      return _lastresult;
+    }
+    data[i/8] <<= 1;
+    // Now compare the low and high cycle times to see if the bit is a 0 or 1.
+    if (highCycles > lowCycles) {
+      // High cycles are greater than 50us low cycle count, must be a 1.
+      data[i/8] |= 1;
+    }
+    // Else high cycles are less than (or equal to, a weird case) the 50us low
+    // cycle count so this must be a zero.  Nothing needs to be changed in the
+    // stored data.
   }
 
-  interrupts();
+  DEBUG_PRINTLN(F("Received:"));
+  DEBUG_PRINT(data[0], HEX); DEBUG_PRINT(F(", "));
+  DEBUG_PRINT(data[1], HEX); DEBUG_PRINT(F(", "));
+  DEBUG_PRINT(data[2], HEX); DEBUG_PRINT(F(", "));
+  DEBUG_PRINT(data[3], HEX); DEBUG_PRINT(F(", "));
+  DEBUG_PRINT(data[4], HEX); DEBUG_PRINT(F(" =? "));
+  DEBUG_PRINTLN((data[0] + data[1] + data[2] + data[3]) & 0xFF, HEX);
 
-  /*
-  Serial.println(j, DEC);
-  Serial.print(data[0], HEX); Serial.print(", ");
-  Serial.print(data[1], HEX); Serial.print(", ");
-  Serial.print(data[2], HEX); Serial.print(", ");
-  Serial.print(data[3], HEX); Serial.print(", ");
-  Serial.print(data[4], HEX); Serial.print(" =? ");
-  Serial.println(data[0] + data[1] + data[2] + data[3], HEX);
-  */
-
-  // check we read 40 bits and that the checksum matches
-  if ((j >= 40) && 
-      (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) {
-    return true;
+  // Check we read 40 bits and that the checksum matches.
+  if (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
+    _lastresult = true;
+    return _lastresult;
+  }
+  else {
+    DEBUG_PRINTLN(F("Checksum failure!"));
+    _lastresult = false;
+    return _lastresult;
+  }
 }
 
-
-  return false;
-
+// Expect the signal line to be at the specified level for a period of time and
+// return a count of loop cycles spent at that level (this cycle count can be
+// used to compare the relative time of two pulses).  If more than a millisecond
+// ellapses without the level changing then the call fails with a 0 response.
+// This is adapted from Arduino's pulseInLong function (which is only available
+// in the very latest IDE versions):
+//   https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/wiring_pulse.c
+uint32_t DHT::expectPulse(bool level) {
+  uint32_t count = 0;
+  // On AVR platforms use direct GPIO port access as it's much faster and better
+  // for catching pulses that are 10's of microseconds in length:
+  #ifdef __AVR
+    uint8_t portState = level ? _bit : 0;
+    while ((*portInputRegister(_port) & _bit) == portState) {
+      if (count++ >= _maxcycles) {
+        return 0; // Exceeded timeout, fail.
+      }
+    }
+  // Otherwise fall back to using digitalRead (this seems to be necessary on ESP8266
+  // right now, perhaps bugs in direct port access functions?).
+  #else
+    while (digitalRead(_pin) == level) {
+      if (count++ >= _maxcycles) {
+        return 0; // Exceeded timeout, fail.
+      }
+    }
+  #endif
+
+  return count;
 }

DHT.h

@@ -1,41 +1,71 @@
+/* DHT library
+
+MIT license
+written by Adafruit Industries
+*/
 #ifndef DHT_H
 #define DHT_H
+
 #if ARDUINO >= 100
  #include "Arduino.h"
 #else
  #include "WProgram.h"
 #endif
 
-/* DHT library 
 
-MIT license
-written by Adafruit Industries
-*/
+// Uncomment to enable printing out nice debug messages.
+//#define DHT_DEBUG
 
-// how many timing transitions we need to keep track of. 2 * number bits + extra
-#define MAXTIMINGS 85
+// Define where debug output will be printed.
+#define DEBUG_PRINTER Serial
 
+// Setup debug printing macros.
+#ifdef DHT_DEBUG
+  #define DEBUG_PRINT(...) { DEBUG_PRINTER.print(__VA_ARGS__); }
+  #define DEBUG_PRINTLN(...) { DEBUG_PRINTER.println(__VA_ARGS__); }
+#else
+  #define DEBUG_PRINT(...) {}
+  #define DEBUG_PRINTLN(...) {}
+#endif
+
+// Define types of sensors.
 #define DHT11 11
 #define DHT22 22
 #define DHT21 21
 #define AM2301 21
 
-class DHT {
- private:
-  uint8_t data[6];
-  uint8_t _pin, _type, _count;
-  unsigned long _lastreadtime;
-  boolean firstreading;
 
+class DHT {
   public:
    DHT(uint8_t pin, uint8_t type, uint8_t count=6);
    void begin(void);
    float readTemperature(bool S=false);
    float convertCtoF(float);
    float convertFtoC(float);
-  float computeHeatIndex(float tempFahrenheit, float percentHumidity);
+   float computeHeatIndex(float temperature, float percentHumidity, bool isFahrenheit=true);
    float readHumidity(void);
    boolean read(void);
 
+ private:
+  uint8_t data[6];
+  uint8_t _pin, _type, _bit, _port;
+  uint32_t _lastreadtime, _maxcycles;
+  bool _firstreading;
+  bool _lastresult;
+
+  uint32_t expectPulse(bool level);
+
 };
+
+class InterruptLock {
+  public:
+   InterruptLock() {
+    noInterrupts();
+   }
+   ~InterruptLock() {
+    interrupts();
+   }
+
+};
+
 #endif

examples/DHTtester/DHTtester.ino

@@ -17,16 +17,11 @@
 // Connect pin 4 (on the right) of the sensor to GROUND
 // Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor
 
-// Initialize DHT sensor for normal 16mhz Arduino
+// Initialize DHT sensor.
+// Note that older versions of this library took an optional third parameter to
+// tweak the timings for faster processors.  This parameter is no longer needed
+// as the current DHT reading algorithm adjusts itself to work on faster procs.
 DHT dht(DHTPIN, DHTTYPE);
-// NOTE: For working with a faster chip, like an Arduino Due or Teensy, you
-// might need to increase the threshold for cycle counts considered a 1 or 0.
-// You can do this by passing a 3rd parameter for this threshold.  It's a bit
-// of fiddling to find the right value, but in general the faster the CPU the
-// higher the value.  The default for a 16mhz AVR is a value of 6.  For an
-// Arduino Due that runs at 84mhz a value of 30 works.
-// Example to initialize DHT sensor for Arduino Due:
-//DHT dht(DHTPIN, DHTTYPE, 30);
 
 void setup() {
   Serial.begin(9600);
@@ -42,9 +37,9 @@ void loop() {
   // Reading temperature or humidity takes about 250 milliseconds!
   // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
   float h = dht.readHumidity();
-  // Read temperature as Celsius
+  // Read temperature as Celsius (the default)
   float t = dht.readTemperature();
-  // Read temperature as Fahrenheit
+  // Read temperature as Fahrenheit (isFahrenheit = true)
   float f = dht.readTemperature(true);
 
   // Check if any reads failed and exit early (to try again).
@@ -53,9 +48,10 @@ void loop() {
     return;
   }
 
-  // Compute heat index
-  // Must send in temp in Fahrenheit!
-  float hi = dht.computeHeatIndex(f, h);
+  // Compute heat index in Fahrenheit (the default)
+  float hif = dht.computeHeatIndex(f, h);
+  // Compute heat index in Celsius (isFahreheit = false)
+  float hic = dht.computeHeatIndex(t, h, false);
 
   Serial.print("Humidity: ");
   Serial.print(h);
@@ -66,6 +62,8 @@ void loop() {
   Serial.print(f);
   Serial.print(" *F\t");
   Serial.print("Heat index: ");
-  Serial.print(hi);
+  Serial.print(hic);
+  Serial.print(" *C ");
+  Serial.print(hif);
   Serial.println(" *F");
 }

keywords.txt

@@ -0,0 +1,22 @@
+###########################################
+# Syntax Coloring Map For DHT-sensor-library
+###########################################
+
+###########################################
+# Datatypes (KEYWORD1)
+###########################################
+
+DHT	KEYWORD1
+
+###########################################
+# Methods and Functions (KEYWORD2)
+###########################################
+
+begin KEYWORD2
+readTemperature KEYWORD2
+convertCtoF KEYWORD2
+convertFtoC KEYWORD2
+computeHeatIndex KEYWORD2
+readHumidity KEYWORD2
+read KEYWORD2
+

library.properties

@@ -1,5 +1,5 @@
 name=DHT sensor library
-version=1.0.0
+version=1.1.1
 author=Adafruit
 maintainer=Adafruit <info@adafruit.com>
 sentence=Arduino library for DHT11, DHT22, etc Temp & Humidity Sensors