fix negative temperature (from DHTNew) (#13)

DHTStable.cpp

@@ -1,12 +1,13 @@
 //
 //    FILE: DHTStable.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 1.0.1
+// VERSION: 1.1.0
 // PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
 //     URL: https://github.com/RobTillaart/DHTstable
 //
 //  HISTORY:
 
+//  1.1.0   2021-11-06  fix DHTNew-#67 negative temperature 
 //  1.0.1   2021-06-01  change architecture to fix incompatible flag.
 //  1.0.0   2021-05-26  rename files and class to DHTStable to fix incompatible flag.
 //                      changed temperature and humidity to private
@@ -82,16 +83,16 @@ int DHTStable::read11(uint8_t pin)
     }
 
     // CONVERT AND STORE
-    _humidity = bits[0] + bits[1] * 0.1;
-    _temperature = (bits[2] & 0x7F) + bits[3] * 0.1;
-    if (bits[2] & 0x80)  // negative temperature
+    _humidity = _bits[0] + _bits[1] * 0.1;
+    _temperature = (_bits[2] & 0x7F) + _bits[3] * 0.1;
+    if (_bits[2] & 0x80)  // negative temperature
     {
         _temperature = -_temperature;
     }
 
     // TEST CHECKSUM
-    uint8_t sum = bits[0] + bits[1] + bits[2] + bits[3];
-    if (bits[4] != sum)
+    uint8_t sum = _bits[0] + _bits[1] + _bits[2] + _bits[3];
+    if (_bits[4] != sum)
     {
       return DHTLIB_ERROR_CHECKSUM;
     }
@@ -111,19 +112,28 @@ int DHTStable::read(uint8_t pin)
     if (_disableIRQ) interrupts();
     if (rv != DHTLIB_OK)
     {
-        _humidity    = DHTLIB_INVALID_VALUE;  // NaN prefered?
-        _temperature = DHTLIB_INVALID_VALUE;  // NaN prefered?
+        _humidity    = DHTLIB_INVALID_VALUE;  // NaN preferred?
+        _temperature = DHTLIB_INVALID_VALUE;  // NaN preferred?
         return rv; // propagate error value
     }
-
     // CONVERT AND STORE
-    _humidity  = word(bits[0], bits[1]) * 0.1;
-    int16_t t = bits[2] * 256 + bits[3];
-    _temperature = t * 0.1;
-
+    _humidity  = word(_bits[0], _bits[1]) * 0.1;
+    int16_t t = ((_bits[2] & 0x7F) * 256 + _bits[3]);
+    if (t == 0)
+    {
+      _temperature = 0.0;     // prevent -0.0;
+    }
+    else
+    {
+      _temperature = t * 0.1;
+      if((_bits[2] & 0x80) == 0x80 )
+      {
+        _temperature = -_temperature;
+      }
+    }
     // TEST CHECKSUM
-    uint8_t sum = bits[0] + bits[1] + bits[2] + bits[3];
-    if (bits[4] != sum)
+    uint8_t sum = _bits[0] + _bits[1] + _bits[2] + _bits[3];
+    if (_bits[4] != sum)
     {
         return DHTLIB_ERROR_CHECKSUM;
     }
@@ -146,7 +156,7 @@ int DHTStable::_readSensor(uint8_t pin, uint8_t wakeupDelay)
     uint8_t idx = 0;
 
     // EMPTY BUFFER
-    for (uint8_t i = 0; i < 5; i++) bits[i] = 0;
+    for (uint8_t i = 0; i < 5; i++) _bits[i] = 0;
 
     // REQUEST SAMPLE
     pinMode(pin, OUTPUT);
@@ -168,7 +178,7 @@ int DHTStable::_readSensor(uint8_t pin, uint8_t wakeupDelay)
         if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;
     }
 
-    // READ THE OUTPUT - 40 BITS => 5 BYTES
+    // READ THE OUTPUT - 40 _bits => 5 BYTES
     for (uint8_t i = 40; i != 0; i--)
     {
         loopCnt = DHTLIB_TIMEOUT;
@@ -187,7 +197,7 @@ int DHTStable::_readSensor(uint8_t pin, uint8_t wakeupDelay)
 
         if ((micros() - t) > 40)
         {
-            bits[idx] |= mask;
+            _bits[idx] |= mask;
         }
         mask >>= 1;
         if (mask == 0)   // next byte?

DHTStable.h

@@ -2,7 +2,7 @@
 //
 //    FILE: DHTStable.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 1.0.1
+// VERSION: 1.1.0
 // PURPOSE: DHT Temperature & Humidity Sensor library for Arduino
 //     URL: https://github.com/RobTillaart/DHTstable
 //
@@ -13,7 +13,7 @@
 
 #include "Arduino.h"
 
-#define DHTSTABLE_LIB_VERSION           (F("1.0.1 - DHTStable"))
+#define DHTSTABLE_LIB_VERSION           (F("1.1.0 - DHTStable"))
 
 
 const int DHTLIB_OK              = 0;
@@ -26,8 +26,8 @@ const int DHTLIB_DHT_WAKEUP      = 1;
 
 
 // max timeout is 100usec.
-// For a 16Mhz proc that is max 1600 clock cycles
-// loops using TIMEOUT use at least 4 clock cycli
+// For a 16Mhz processor that is max 1600 clock cycles
+// loops using TIMEOUT use at least 4 clock cycles
 // so 100 us takes max 400 loops
 // so by dividing F_CPU by 40000 we "fail" as fast as possible
 const int DHTLIB_TIMEOUT = (F_CPU/40000);
@@ -54,7 +54,7 @@ class DHTStable
     inline int read44(uint8_t pin)   { return read(pin); };   // ok
     inline int read2301(uint8_t pin) { return read(pin); };   // ok
     inline int read2302(uint8_t pin) { return read(pin); };   // ok
-    inline int read2320(uint8_t pin) { return read(pin); };   //.ok
+    inline int read2320(uint8_t pin) { return read(pin); };   // ok
     inline int read2322(uint8_t pin) { return read(pin); };   // ok
 
     // read values from cache, call read() to refresh!
@@ -65,7 +65,7 @@ class DHTStable
     void  setDisableIRQ(bool b )       { _disableIRQ = b; };
 
 private:
-    uint8_t bits[5];  // buffer to receive data
+    uint8_t _bits[5];  // buffer to receive data
     int     _readSensor(uint8_t pin, uint8_t wakeupDelay);
     bool    _disableIRQ = false;
     float   _humidity;

library.json

@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/DHTstable.git"
   },
-  "version": "1.0.1",
+  "version": "1.1.0",
   "license": "MIT",
   "frameworks": "arduino",
   "platforms": "*"

library.properties

@@ -1,5 +1,5 @@
 name=DHTStable
-version=1.0.1
+version=1.1.0
 author=Rob Tillaart <[email protected]>
 maintainer=Rob Tillaart <[email protected]>
 sentence=Stable version of library for DHT Temperature & Humidity Sensor