Merge pull request #1501 from fl43/patch-1

Fix voltage calculation - Update mkr-battery-app-note.md

Author: jhansson-ard

content/hardware/01.mkr/01.boards/mkr-wifi-1010/tutorials/mkr-battery-app-note/mkr-battery-app-note.md

@@ -124,7 +124,7 @@ We will go through the lines needed to create a Sketch to read the battery value
 **4.** We will now create a variable to store the maximum source voltage `max_Source_voltage` as well as the upper (`batteryFullVoltage`) and lower (`batteryEmptyVoltage`) values for the battery. We will also define the battery capacity as `batteryCapacity` so as to determine the charging current. Since we are using a 750 mAh battery in this example, we will set the value to `0.750`.
 
 ```arduino
-  int max_Source_voltage;
+  float max_Source_voltage;
 
   float batteryFullVoltage = 4.2;
   float batteryEmptyVoltage = 3.3;
@@ -185,12 +185,13 @@ void loop()
 **13.** In order to convert `rawADC` into a voltage reading (`voltADC`) we will divide `rawADC` by 4095 and then multiply it by the analog reference voltage (3.3V). 
 
 ```arduino
-voltADC = rawADC * (3.3/4095.0);
+voltADC = rawADC * 3.3 / 4096.0;
 ```
 
-**14.** The `voltADC` variable gives us the voltage sensed directly on the PB09 pin. This voltage is passed through the voltage divider, so it is a fraction of the actual battery voltage. We can then calculate the equivilanet battery voltage as follows.
+**14.** The `voltADC` variable gives us the voltage sensed directly on the PB09 pin. This voltage is passed through the voltage divider, so it is a fraction of the actual battery voltage. We can then calculate the equivalent battery voltage as follows.
+
 ```arduino
-voltBat = voltADC * (max_Source_voltage/3.3);
+voltBat = max_Source_voltage * rawADC / 4096.0;
 ```
 
 **15.** We can approximate the battery voltage to be proportional to the capacity level. Since the `map()` function does not work with float variables, we will manually map the values.
@@ -266,7 +267,7 @@ float voltBat;          //calculated voltage on battery
 int R1 =  330000;       // resistor between battery terminal and SAMD pin PB09
 int R2 = 1000000;       // resistor between SAMD pin PB09 and ground
 
-int max_Source_voltage; // upper source voltage for the battery
+float max_Source_voltage; // upper source voltage for the battery
 
 // define voltage at which battery is full/empty
 float batteryFullVoltage = 4.2;   //upper voltage limit for battery
@@ -303,8 +304,8 @@ void loop()
 {
   
   rawADC = analogRead(ADC_BATTERY);                     //the value obtained directly at the PB09 input pin
-  voltADC = rawADC * (3.3/4095.0);                      //convert ADC value to the voltage read at the pin
-  voltBat = voltADC * (max_Source_voltage/3.3);         //we cannot use map since it requires int inputs/outputs
+  voltADC = rawADC * 3.3 / 4096.0;                      //convert ADC value to the voltage read at the pin
+  voltBat = max_Source_voltage * rawADC / 4096.0;       //we cannot use map since it requires int inputs/outputs
   
   int new_batt = (voltBat - batteryEmptyVoltage) * (100) / (batteryFullVoltage - batteryEmptyVoltage);    //custom float friendly map function