Updated default vref to be NAN. Made vref an optional constructor arg

drivers/AnalogIn.h

@@ -25,6 +25,8 @@
 #include "platform/SingletonPtr.h"
 #include "platform/PlatformMutex.h"
 
+#include <cmath>
+
 namespace mbed {
 /** \defgroup mbed-os-public Public API */
 
@@ -71,14 +73,14 @@ public:
      *
      * @param pinmap reference to structure which holds static pinmap.
      */
-    AnalogIn(const PinMap &pinmap);
-    AnalogIn(const PinMap &&) = delete; // prevent passing of temporary objects
+    AnalogIn(const PinMap &pinmap, float vref = MBED_CONF_TARGET_DEFAULT_ADC_VREF);
+    AnalogIn(const PinMap &&, float vref = MBED_CONF_TARGET_DEFAULT_ADC_VREF) = delete; // prevent passing of temporary objects
 
     /** Create an AnalogIn, connected to the specified pin
      *
      * @param pin AnalogIn pin to connect to
      */
-    AnalogIn(PinName pin);
+    AnalogIn(PinName pin, float vref = MBED_CONF_TARGET_DEFAULT_ADC_VREF);
 
     /** Read the input voltage, represented as a float in the range [0.0, 1.0]
      *
@@ -161,7 +163,7 @@ protected:
     analogin_t _adc;
     static SingletonPtr<PlatformMutex> _mutex;
 
-    float vref;
+    float _vref;
 
 #endif //!defined(DOXYGEN_ONLY)
 

drivers/source/AnalogIn.cpp

@@ -23,21 +23,21 @@ namespace mbed {
 
 SingletonPtr<PlatformMutex> AnalogIn::_mutex;
 
-AnalogIn::AnalogIn(PinName pin) : vref(MBED_CONF_TARGET_DEFAULT_ADC_VREF)
+
+AnalogIn::AnalogIn(PinName pin, float vref) : _vref(vref)
 {
     lock();
     analogin_init(&_adc, pin);
     unlock();
 }
 
-AnalogIn::AnalogIn(const PinMap &pinmap) : vref(MBED_CONF_TARGET_DEFAULT_ADC_VREF)
+AnalogIn::AnalogIn(const PinMap &pinmap, float vref) : _vref(vref)
 {
     lock();
     analogin_init_direct(&_adc, &pinmap);
     unlock();
 }
 
-
 float AnalogIn::read()
 {
     lock();
@@ -56,17 +56,17 @@ unsigned short AnalogIn::read_u16()
 
 float AnalogIn::read_voltage()
 {
-    return (this->read() * this->vref);
+    return (this->read() * this->_vref);
 }
 
 void AnalogIn::set_reference_voltage(float vref)
 {
-    this->vref = vref;
+    this->_vref = vref;
 }
 
 float AnalogIn::get_reference_voltage(void)
 {
-    return this->vref;
+    return this->_vref;
 }
 
 } // namespace mbed

targets/targets.json

@@ -83,7 +83,7 @@
             },
             "default-adc-vref": {
                 "help": "Default reference voltage for ADC (float)",
-                "value": "3.3f"
+                "value": "NAN"
             }
         }
     },