Extend AnalogIn API: read_voltage

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 */
 
@@ -70,15 +72,21 @@ class AnalogIn {
     /** Create an AnalogIn, connected to the specified pin
      *
      * @param pinmap reference to structure which holds static pinmap.
+     * @param vref (optional) Reference voltage of this AnalogIn instance (defaults to target.default-adc-vref).
+     *
+     * @note An input voltage at or above the given vref value will produce a 1.0 result when `read` is called
      */
-    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
+     * @param vref (optional) Reference voltage of this AnalogIn instance (defaults to target.default-adc-vref).
+     *
+     * @note An input voltage at or above the given vref value will produce a 1.0 result when `read` is called
      */
-    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]
      *
@@ -93,6 +101,35 @@ class AnalogIn {
      */
     unsigned short read_u16();
 
+    /**
+     * Read the input voltage in volts. The output depends on the target board's
+     * ADC reference voltage (typically equal to supply voltage). The ADC reference voltage
+     * sets the maximum voltage the ADC can quantify (ie: ADC output == ADC_MAX_VALUE when Vin == Vref)
+     *
+     * The target's default ADC reference voltage is determined by the configuration
+     * option target.default-adc_vref. The reference voltage for a particular input
+     * can be manually specified by either the constructor or `AnalogIn::set_reference_voltage`.
+     *
+     * @returns A floating-point value representing the current input voltage, measured in volts.
+     */
+    float read_voltage();
+
+    /**
+     * Sets this AnalogIn instance's reference voltage.
+     *
+     * The AnalogIn's reference voltage is used to scale the output when calling AnalogIn::read_volts
+     *
+     * @param[in] vref New ADC reference voltage for this AnalogIn instance.
+     */
+    void set_reference_voltage(float vref);
+
+    /**
+     * Gets this AnalogIn instance's reference voltage.
+     *
+     * @returns A floating-point value representing this AnalogIn's reference voltage, measured in volts.
+     */
+    float get_reference_voltage() const;
+
     /** An operator shorthand for read()
      *
      * The float() operator can be used as a shorthand for read() to simplify common code sequences
@@ -131,6 +168,9 @@ class AnalogIn {
 
     analogin_t _adc;
     static SingletonPtr<PlatformMutex> _mutex;
+
+    float _vref;
+
 #endif //!defined(DOXYGEN_ONLY)
 
 };

drivers/source/AnalogIn.cpp

@@ -23,21 +23,21 @@ namespace mbed {
 
 SingletonPtr<PlatformMutex> AnalogIn::_mutex;
 
-AnalogIn::AnalogIn(PinName pin)
+
+AnalogIn::AnalogIn(PinName pin, float vref) : _vref(vref)
 {
     lock();
     analogin_init(&_adc, pin);
     unlock();
 }
 
-AnalogIn::AnalogIn(const PinMap &pinmap)
+AnalogIn::AnalogIn(const PinMap &pinmap, float vref) : _vref(vref)
 {
     lock();
     analogin_init_direct(&_adc, &pinmap);
     unlock();
 }
 
-
 float AnalogIn::read()
 {
     lock();
@@ -54,6 +54,21 @@ unsigned short AnalogIn::read_u16()
     return ret;
 }
 
+float AnalogIn::read_voltage()
+{
+    return read() * _vref;
+}
+
+void AnalogIn::set_reference_voltage(float vref)
+{
+    _vref = vref;
+}
+
+float AnalogIn::get_reference_voltage(void) const
+{
+    return _vref;
+}
+
 } // namespace mbed
 
 #endif

targets/targets.json

@@ -80,6 +80,10 @@
             "xip-enable": {
                 "help": "Enable Execute In Place (XIP) on this target. Value is only significant if the board has executable external storage such as QSPIF. If this is enabled, customize the linker file to choose what text segments are placed on external storage",
                 "value": false
+            },
+            "default-adc-vref": {
+                "help": "Default reference voltage for ADC (float)",
+                "value": "NAN"
             }
         }
     },

tools/test/travis-ci/doxy-spellchecker/ignore.en.pws

@@ -114,4 +114,6 @@ api
 uart
 chrono
 Hinnant
+Vin
+Vref
 _doxy_