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Fix voltage calculation - Update mkr-battery-app-note.md #1501

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Fix voltage calculation - Update mkr-battery-app-note.md #1501

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Update mkr-battery-app-note.md
fl43 Nov 16, 2023
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Update mkr-battery-app-note.md
fl43 Nov 16, 2023
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12 changes: 6 additions & 6 deletions .../01.boards/mkr-wifi-1010/tutorials/mkr-battery-app-note/mkr-battery-app-note.md
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -185,12 +185,12 @@ 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.
```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.
Expand Down Expand Up @@ -266,7 +266,7 @@ 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
Expand Down Expand Up @@ -303,8 +303,8 @@ 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

Expand Down