How can I measure the battery level in a Lolin D32 pro?

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1

Hi,

How can I measure the battery level of a Lolin d32 pro?

I'm trying with this code

  int ADC_VALUE = analogRead(35);
  Serial.print("ADC VALUE = ");
  Serial.println(ADC_VALUE);
  int adc_percentage = int(100 * ADC_VALUE / 4095);
  float voltage_value = (ADC_VALUE * 3.3 ) / (4095);
  Serial.print("Voltage = ");
  Serial.print(voltage_value);
  Serial.println(" volts");

I get this output

ADC VALUE = 2485
Voltage = 2.00

that is correct?

Any suggestions are welcome.

Regards

2

A/D converters basically work by comparing your voltage with another voltage. Therefore, you will have to investigate how your A/D converter measures the battery voltage. Because if the battery voltage is the voltage the microcontroller uses as a reference in case it is its supply voltage, you will always measure the battery to be full.

You need to configure the A/D converter in a way that it gets a stable reference voltage. There are many that have an internal reference voltage (e.g. a bandgap reference voltage) or you can get an external one.

Have a look into the datasheet of your micro and then see how the library you are using is setting up the A/D converter.

3

The ESP8266 has a built-in voltage reference of about 1V, afaik the ESP32 works the same. The development boards add a voltage divider (typically 220k+100k) to give it a 3.3V range.

So measuring the battery voltage is no problem this way, just be aware of the on-board voltage divider when adding your own.

That just leaves the minor issue of there not being much of a relationship between battery voltage and battery charge level, making this voltage measurement kinda useless for determining battery level.