What is the formula for calculating battery voltage?

ahendml · August 19, 2024, 12:47pm

honvl/Seeed-Xiao-NRF52840-Battery/blob/main/xiaobattery.h

#include <Arduino.h>
#include <bluefruit.h>

#define BAT_HIGH_CHARGE 22  // HIGH for 50mA, LOW for 100mA
#define BAT_CHARGE_STATE 23 // LOW for charging, HIGH not charging

class Xiao {
public:
  Xiao();
  float GetBatteryVoltage();
  bool IsChargingBattery();
};

Xiao::Xiao() {
  pinMode(VBAT_ENABLE, OUTPUT);
  pinMode(BAT_CHARGE_STATE, INPUT);

  digitalWrite(BAT_HIGH_CHARGE, HIGH); // charge with 50mA
}

This file has been truncated. show original

I am trying to get the battery voltage using seeed xiao nrf52840
I use the library above and it works well
But how do I get the VBAT_MV_PER_LBS (0.003395996F) value here?
I know the formula for getting the battery voltage through the adc voltage division is as below. Am I wrong?
Thank you
Power voltage * adcValue / resolution (4096) * R2 / (R1 + R2)