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#define VBAT_PIN (A7)
#define VBAT_MV_PER_LSB (0.73242188F) // 3.0V ADC range and 12-bit ADC resolution = 3000mV/4096
#define VBAT_DIVIDER (0.71275837F) // 2M + 0.806M voltage divider on VBAT = (2M / (0.806M + 2M))
#define VBAT_DIVIDER_COMP (1.403F) // Compensation factor for the VBAT divider
int readVBAT(void) {
int raw;
// Set the analog reference to 3.0V (default = 3.6V)
analogReference(AR_INTERNAL_3_0);
// Set the resolution to 12-bit (0..4095)
analogReadResolution(12); // Can be 8, 10, 12 or 14
// Let the ADC settle
delay(1);
// Get the raw 12-bit, 0..3000mV ADC value
raw = analogRead(VBAT_PIN);
// Set the ADC back to the default settings
analogReference(AR_DEFAULT);
analogReadResolution(10);
return raw;
}
uint8_t mvToPercent(float mvolts) {
uint8_t battery_level;
if (mvolts >= 3000)
{
battery_level = 100;
}
else if (mvolts > 2900)
{
battery_level = 100 - ((3000 - mvolts) * 58) / 100;
}
else if (mvolts > 2740)
{
battery_level = 42 - ((2900 - mvolts) * 24) / 160;
}
else if (mvolts > 2440)
{
battery_level = 18 - ((2740 - mvolts) * 12) / 300;
}
else if (mvolts > 2100)
{
battery_level = 6 - ((2440 - mvolts) * 6) / 340;
}
else
{
battery_level = 0;
}
return battery_level;
}
void setup() {
Serial.begin(115200);
while ( !Serial ) delay(10); // for nrf52840 with native usb
// Get a single ADC sample and throw it away
readVBAT();
}
void loop() {
// Get a raw ADC reading
int vbat_raw = readVBAT();
// Convert from raw mv to percentage (based on LIPO chemistry)
uint8_t vbat_per = mvToPercent(vbat_raw * VBAT_MV_PER_LSB);
// Convert the raw value to compensated mv, taking the resistor-
// divider into account (providing the actual LIPO voltage)
// ADC range is 0..3000mV and resolution is 12-bit (0..4095),
// VBAT voltage divider is 2M + 0.806M, which needs to be added back
float vbat_mv = (float)vbat_raw * VBAT_MV_PER_LSB * VBAT_DIVIDER_COMP;
// Display the results
Serial.print("ADC = ");
Serial.print(vbat_raw * VBAT_MV_PER_LSB);
Serial.print(" mV (");
Serial.print(vbat_raw);
Serial.print(") ");
Serial.print("LIPO = ");
Serial.print(vbat_mv);
Serial.print(" mV (");
Serial.print(vbat_per);
Serial.println("%)");
delay(1000);
}
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