Added API call to return ADC reading in volts, scaled by configurable system ADC reference voltage.

Author: AGlass0fMilk

drivers/AnalogIn.h

@@ -93,6 +93,16 @@ 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: Vin == Vref when ADC output == ADC_MAX_VALUE)
+     *
+     * The target's ADC reference voltage can be configured by overriding "drivers.adc_vref"
+     *
+     * @returns A floating-point value representing the current input voltage, measured in volts.
+     */
+    float read_volts();
+
     /** An operator shorthand for read()
      *
      * The float() operator can be used as a shorthand for read() to simplify common code sequences

drivers/mbed_lib.json

@@ -41,6 +41,9 @@
         "qspi_csn": {
             "help": "QSPI chip select pin",
             "value": "QSPI_FLASH1_CSN"
-        }
+        },
+        "adc_vref": {
+            "help": "Reference voltage for ADC (float)",
+            "value": 3.3f
     }
 }

drivers/source/AnalogIn.cpp

@@ -54,6 +54,11 @@ unsigned short AnalogIn::read_u16()
     return ret;
 }
 
+float AnalogIn::read_volts() {
+    float ret = this->read();
+    return (ret*MBED_CONF_DRIVERS_ADC_VREF);
+}
+
 } // namespace mbed
 
 #endif