Configurable pullup delay time, default 55 usec

Author: PaintYourDragon

DHT.cpp

@@ -22,14 +22,17 @@ DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
   // based on the speed of the processor.
 }
 
-void DHT::begin(void) {
+// Optionally pass pull-up time (in microseconds) before DHT reading starts.
+// Default is 55 (see function declaration in DHT.h).
+void DHT::begin(uint8_t usec) {
   // set up the pins!
   pinMode(_pin, INPUT_PULLUP);
   // Using this value makes sure that millis() - lastreadtime will be
   // >= MIN_INTERVAL right away. Note that this assignment wraps around,
   // but so will the subtraction.
   _lastreadtime = millis() - MIN_INTERVAL;
   DEBUG_PRINT("DHT max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC);
+  pullTime = usec;
 }
 
 //boolean S == Scale.  True == Fahrenheit; False == Celcius
@@ -179,8 +182,10 @@ bool DHT::read(bool force) {
     // End the start signal by setting data line high for 40 microseconds.
     pinMode(_pin, INPUT_PULLUP);
 
+    // Delay a moment to let sensor pull data line low.
+    delayMicroseconds(pullTime);
+
     // Now start reading the data line to get the value from the DHT sensor.
-    delayMicroseconds(40);  // Delay a bit to let sensor pull data line low.
 
     // Turn off interrupts temporarily because the next sections
     // are timing critical and we don't want any interruptions.

DHT.h

@@ -39,7 +39,7 @@ written by Adafruit Industries
 class DHT {
   public:
    DHT(uint8_t pin, uint8_t type, uint8_t count=6);
-   void begin(void);
+   void begin(uint8_t usec=55);
    float readTemperature(bool S=false, bool force=false);
    float convertCtoF(float);
    float convertFtoC(float);
@@ -58,6 +58,7 @@ class DHT {
   #endif
   uint32_t _lastreadtime, _maxcycles;
   bool _lastresult;
+  uint8_t pullTime; // Time (in usec) to pull up data line before reading
 
   uint32_t expectPulse(bool level);
 

library.properties

@@ -1,5 +1,5 @@
 name=DHT sensor library
-version=1.3.2
+version=1.3.3
 author=Adafruit
 maintainer=Adafruit <[email protected]>
 sentence=Arduino library for DHT11, DHT22, etc Temp & Humidity Sensors