Disable clock stretching

Since not all platforms support clock streching, use the
measurement commands with disabled clock streching

Author: psachs

SHTSensor.cpp

@@ -51,13 +51,14 @@ bool SHTSensorDriver::readSample()
 // class SHTI2cSensor
 //
 
-const uint8_t SHTI2cSensor::CMD_SIZE            = 2;
-const uint8_t SHTI2cSensor::EXPECTED_DATA_SIZE  = 6;
+const uint8_t SHTI2cSensor::CMD_SIZE             = 2;
+const uint8_t SHTI2cSensor::EXPECTED_DATA_SIZE   = 6;
 
 bool SHTI2cSensor::readFromI2c(uint8_t i2cAddress,
                                const uint8_t *i2cCommand,
                                uint8_t commandLength, uint8_t *data,
-                               uint8_t dataLength)
+                               uint8_t dataLength,
+                               uint8_t duration)
 {
   Wire.beginTransmission(i2cAddress);
   for (int i = 0; i < commandLength; ++i) {
@@ -70,6 +71,8 @@ bool SHTI2cSensor::readFromI2c(uint8_t i2cAddress,
     return false;
   }
 
+  delay(duration);
+
   Wire.requestFrom(i2cAddress, dataLength);
 
   // check if the same number of bytes are received that are requested.
@@ -113,7 +116,7 @@ bool SHTI2cSensor::readSample()
   cmd[1] = mI2cCommand & 0xff;
 
   if (!readFromI2c(mI2cAddress, cmd, CMD_SIZE, data,
-                   EXPECTED_DATA_SIZE)) {
+                   EXPECTED_DATA_SIZE, mDuration)) {
     return false;
   }
 
@@ -144,8 +147,8 @@ class SHTC1Sensor : public SHTI2cSensor
 {
 public:
     SHTC1Sensor()
-        // Using clock stretching, high precision, T first
-        : SHTI2cSensor(0x70, 0x7ca2, -45, 175, 65535, 100, 65535)
+        // clock stretching disabled, high precision, T first
+        : SHTI2cSensor(0x70, 0x7866, 15, -45, 175, 65535, 100, 65535)
     {
     }
 };
@@ -158,16 +161,21 @@ class SHTC1Sensor : public SHTI2cSensor
 class SHT3xSensor : public SHTI2cSensor
 {
 private:
-  static const uint16_t SHT3X_ACCURACY_HIGH    = 0x2c06;
-  static const uint16_t SHT3X_ACCURACY_MEDIUM  = 0x2c0d;
-  static const uint16_t SHT3X_ACCURACY_LOW     = 0x2c10;
+  static const uint16_t SHT3X_ACCURACY_HIGH    = 0x2400;
+  static const uint16_t SHT3X_ACCURACY_MEDIUM  = 0x240b;
+  static const uint16_t SHT3X_ACCURACY_LOW     = 0x2416;
+
+  static const uint8_t SHT3X_ACCURACY_HIGH_DURATION   = 15;
+  static const uint8_t SHT3X_ACCURACY_MEDIUM_DURATION = 6;
+  static const uint8_t SHT3X_ACCURACY_LOW_DURATION    = 4;
 
 public:
   static const uint8_t SHT3X_I2C_ADDRESS_44 = 0x44;
   static const uint8_t SHT3X_I2C_ADDRESS_45 = 0x45;
 
   SHT3xSensor(uint8_t i2cAddress = SHT3X_I2C_ADDRESS_44)
       : SHTI2cSensor(i2cAddress, SHT3X_ACCURACY_HIGH,
+                     SHT3X_ACCURACY_HIGH_DURATION,
                      -45, 175, 65535, 100, 65535)
   {
   }
@@ -177,12 +185,15 @@ class SHT3xSensor : public SHTI2cSensor
     switch (newAccuracy) {
       case SHTSensor::SHT_ACCURACY_HIGH:
         mI2cCommand = SHT3X_ACCURACY_HIGH;
+        mDuration = SHT3X_ACCURACY_HIGH_DURATION;
         break;
       case SHTSensor::SHT_ACCURACY_MEDIUM:
         mI2cCommand = SHT3X_ACCURACY_MEDIUM;
+        mDuration = SHT3X_ACCURACY_MEDIUM_DURATION;
         break;
       case SHTSensor::SHT_ACCURACY_LOW:
         mI2cCommand = SHT3X_ACCURACY_LOW;
+        mDuration = SHT3X_ACCURACY_LOW_DURATION;
         break;
       default:
         return false;

SHTSensor.h

@@ -202,11 +202,12 @@ class SHTI2cSensor : public SHTSensorDriver {
    * and the values `x' and `y' to convert the fixed-point humidity value
    * received by the sensor to a floating point value using the formula:
    * humidity = x * (rawHumidity / y)
+   * duration is the duration in milliseconds of one measurement
    */
-  SHTI2cSensor(uint8_t i2cAddress, uint16_t i2cCommand,
+  SHTI2cSensor(uint8_t i2cAddress, uint16_t i2cCommand, uint8_t duration,
                float a, float b, float c,
                float x, float y)
-      : mI2cAddress(i2cAddress), mI2cCommand(i2cCommand),
+      : mI2cAddress(i2cAddress), mI2cCommand(i2cCommand), mDuration(duration),
         mA(a), mB(b), mC(c), mX(x), mY(y)
   {
   }
@@ -219,6 +220,7 @@ class SHTI2cSensor : public SHTSensorDriver {
 
   uint8_t mI2cAddress;
   uint16_t mI2cCommand;
+  uint8_t mDuration;
   float mA;
   float mB;
   float mC;
@@ -230,7 +232,7 @@ class SHTI2cSensor : public SHTSensorDriver {
   static bool readFromI2c(uint8_t i2cAddress,
                           const uint8_t *i2cCommand,
                           uint8_t commandLength, uint8_t *data,
-                          uint8_t dataLength);
+                          uint8_t dataLength, uint8_t duration);
 };
 
 class SHT3xAnalogSensor