Async

DHT.cpp

@@ -33,32 +33,11 @@ void DHT::begin(void) {
 
 //boolean S == Scale.  True == Fahrenheit; False == Celcius
 float DHT::readTemperature(bool S, bool force) {
-  float f = NAN;
-
-  if (read(force)) {
-    switch (_type) {
-    case DHT11:
-      f = data[2];
-      if(S) {
-        f = convertCtoF(f);
-      }
-      break;
-    case DHT22:
-    case DHT21:
-      f = data[2] & 0x7F;
-      f *= 256;
-      f += data[3];
-      f *= 0.1;
-      if (data[2] & 0x80) {
-        f *= -1;
-      }
-      if(S) {
-        f = convertCtoF(f);
-      }
-      break;
-    }
-  }
-  return f;
+  //Argument <<force>> is kept only for back-compatibility
+  if(S) 
+    return this->convertCtoF(this->_temperature);
+  else
+    return this->_temperature;
 }
 
 float DHT::convertCtoF(float c) {
@@ -70,22 +49,8 @@ float DHT::convertFtoC(float f) {
 }
 
 float DHT::readHumidity(bool force) {
-  float f = NAN;
-  if (read()) {
-    switch (_type) {
-    case DHT11:
-      f = data[0];
-      break;
-    case DHT22:
-    case DHT21:
-      f = data[0];
-      f *= 256;
-      f += data[1];
-      f *= 0.1;
-      break;
-    }
-  }
-  return f;
+  //Argument <<force>> is kept only for back-compatibility
+  return this->_humidity;
 }
 
 //boolean isFahrenheit: True == Fahrenheit; False == Celcius
@@ -120,30 +85,53 @@ float DHT::computeHeatIndex(float temperature, float percentHumidity, bool isFah
   return isFahrenheit ? hi : convertFtoC(hi);
 }
 
-boolean DHT::read(bool force) {
-  // Check if sensor was read less than two seconds ago and return early
-  // to use last reading.
+
+void DHT::loop(){
   uint32_t currenttime = millis();
-  if (!force && ((currenttime - _lastreadtime) < 2000)) {
-    return _lastresult; // return last correct measurement
-  }
-  _lastreadtime = currenttime;
+  switch(this->state){
+    case IDLE:
+      // Check if sensor was read less than two seconds ago and return early
+      // to use last reading.
+      if((currenttime - _lastreadtime) < 2000)
+        return;
+      this->_lastreadtime = currenttime;
+      this->state = WAITING;
+
+      // Reset 40 bits of received data to zero.
+      data[0] = data[1] = data[2] = data[3] = data[4] = 0;
+
+      // 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);
+      break;
+
+    case WAITING:
+      if((currenttime-_lastreadtime) < 250)
+        return;
+      // First set data line low for 20 milliseconds.
+      pinMode(_pin, OUTPUT);
+      digitalWrite(_pin, LOW);
 
-  // Reset 40 bits of received data to zero.
-  data[0] = data[1] = data[2] = data[3] = data[4] = 0;
+      this->_lastreadtime = currenttime;
+      this->state = READING;
+      break;
 
-  // Send start signal.  See DHT datasheet for full signal diagram:
-  //   http://www.adafruit.com/datasheets/Digital%20humidity%20and%20temperature%20sensor%20AM2302.pdf
+    case READING:
+      if((currenttime-_lastreadtime) < 20)
+        return;
+      this->read();
+      this->state = IDLE;
+
+  }
+}
 
-  // Go into high impedence state to let pull-up raise data line level and
-  // start the reading process.
-  digitalWrite(_pin, HIGH);
-  delay(250);
+boolean DHT::isValid(){
+  return this->_lastresult;
+}
 
-  // First set data line low for 20 milliseconds.
-  pinMode(_pin, OUTPUT);
-  digitalWrite(_pin, LOW);
-  delay(20);
+boolean DHT::read() {
 
   uint32_t cycles[80];
   {
@@ -217,6 +205,20 @@ boolean DHT::read(bool force) {
 
   // Check we read 40 bits and that the checksum matches.
   if (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
+    float t,h;
+    switch (_type) {
+      case DHT11:
+        this->_temperature = data[2];
+        this->_humidity = data[0];
+        break;
+      case DHT22:
+      case DHT21:
+        t = (data[2] & 0x7F) * 256 + data[3];
+        this->_temperature = t * 0.1 * ((data[2] & 0x80) ? -1 : 1);
+        h = data[0] * 256 + data[1];
+        this->_humidity = h * 0.1;
+        break;
+    }
     _lastresult = true;
     return _lastresult;
   }

DHT.h

@@ -44,7 +44,9 @@ class DHT {
    float convertFtoC(float);
    float computeHeatIndex(float temperature, float percentHumidity, bool isFahrenheit=true);
    float readHumidity(bool force=false);
-   boolean read(bool force=false);
+   boolean read();
+   boolean isValid();
+   void loop();
 
  private:
   uint8_t data[5];
@@ -57,7 +59,17 @@ class DHT {
   uint32_t _lastreadtime, _maxcycles;
   bool _lastresult;
 
+  float _temperature, _humidity;
+
+  enum readingStatus{
+    IDLE,
+    WAITING,
+    READING
+  };
+
   uint32_t expectPulse(bool level);
+
+  readingStatus state = IDLE;
 
 };
 

examples/DHT_Unified_Sensor/DHT_Unified_Sensor.ino

@@ -5,7 +5,7 @@
 
 // Depends on the following Arduino libraries:
 // - Adafruit Unified Sensor Library: https://github.com/adafruit/Adafruit_Sensor
-// - DHT Sensor Library: https://github.com/adafruit/DHT-sensor-library
+// - DHT Sensor Library: https://github.com/nos86/DHT-sensor-library#async
 
 #include <Adafruit_Sensor.h>
 #include <DHT.h>
@@ -24,6 +24,7 @@
 DHT_Unified dht(DHTPIN, DHTTYPE);
 
 uint32_t delayMS;
+float lastReading = 0;
 
 void setup() {
   Serial.begin(9600); 
@@ -58,27 +59,30 @@ void setup() {
 }
 
 void loop() {
+  dht.loop();
   // Delay between measurements.
-  delay(delayMS);
-  // Get temperature event and print its value.
-  sensors_event_t event;  
-  dht.temperature().getEvent(&event);
-  if (isnan(event.temperature)) {
-    Serial.println("Error reading temperature!");
-  }
-  else {
-    Serial.print("Temperature: ");
-    Serial.print(event.temperature);
-    Serial.println(" *C");
-  }
-  // Get humidity event and print its value.
-  dht.humidity().getEvent(&event);
-  if (isnan(event.relative_humidity)) {
-    Serial.println("Error reading humidity!");
-  }
-  else {
-    Serial.print("Humidity: ");
-    Serial.print(event.relative_humidity);
-    Serial.println("%");
+  if(mills()-lastReading>delayMS){
+    lastReading = millis();
+    // Get temperature event and print its value.
+    sensors_event_t event;  
+    dht.temperature().getEvent(&event);
+    if (isnan(event.temperature)) {
+      Serial.println("Error reading temperature!");
+    }
+    else {
+      Serial.print("Temperature: ");
+      Serial.print(event.temperature);
+      Serial.println(" *C");
+    }
+    // Get humidity event and print its value.
+    dht.humidity().getEvent(&event);
+    if (isnan(event.relative_humidity)) {
+      Serial.println("Error reading humidity!");
+    }
+    else {
+      Serial.print("Humidity: ");
+      Serial.print(event.relative_humidity);
+      Serial.println("%");
+    }
   }
 }

examples/DHTtester/DHTtester.ino

@@ -1,5 +1,5 @@
 // Example testing sketch for various DHT humidity/temperature sensors
-// Written by ladyada, public domain
+// Written by nos86, public domain
 
 #include "DHT.h"
 
@@ -22,6 +22,7 @@
 // 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);
+float lastReading = 0;
 
 void setup() {
   Serial.begin(9600);
@@ -32,38 +33,40 @@ void setup() {
 
 void loop() {
   // Wait a few seconds between measurements.
-  delay(2000);
-
-  // 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 (the default)
-  float t = dht.readTemperature();
-  // Read temperature as Fahrenheit (isFahrenheit = true)
-  float f = dht.readTemperature(true);
-
-  // Check if any reads failed and exit early (to try again).
-  if (isnan(h) || isnan(t) || isnan(f)) {
-    Serial.println("Failed to read from DHT sensor!");
-    return;
+  dht.loop();
+  if(millis()-lastReading>2000){
+    lastReading = millis();
+    // 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 (the default)
+    float t = dht.readTemperature();
+    // Read temperature as Fahrenheit (isFahrenheit = true)
+    float f = dht.readTemperature(true);
+
+    // Check if any reads failed and exit early (to try again).
+    if (isnan(h) || isnan(t) || isnan(f)) {
+      Serial.println("Failed to read from DHT sensor!");
+      return;
+    }
+
+    // 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);
+    Serial.print(" %\t");
+    Serial.print("Temperature: ");
+    Serial.print(t);
+    Serial.print(" *C ");
+    Serial.print(f);
+    Serial.print(" *F\t");
+    Serial.print("Heat index: ");
+    Serial.print(hic);
+    Serial.print(" *C ");
+    Serial.print(hif);
+    Serial.println(" *F");
   }
-
-  // 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);
-  Serial.print(" %\t");
-  Serial.print("Temperature: ");
-  Serial.print(t);
-  Serial.print(" *C ");
-  Serial.print(f);
-  Serial.print(" *F\t");
-  Serial.print("Heat index: ");
-  Serial.print(hic);
-  Serial.print(" *C ");
-  Serial.print(hif);
-  Serial.println(" *F");
 }

keywords.txt

@@ -19,4 +19,5 @@ convertFtoC KEYWORD2
 computeHeatIndex KEYWORD2
 readHumidity KEYWORD2
 read KEYWORD2
-
+loop KEYWORD2
+isValid KEYWORD2