ESP32_Feather_Vbat_Test.ino

/*
  ESP32 Feather Battery Voltage Monitor.
  This example code is in the public domain.
  Daniel deBeer
*/

#define BAT_SENSE 2     // Sense resistor control pin
#define RLED 13         // Red LED pin
#define ADC_Ch 35       // ADC Used for measuring the battery voltage.  The voltage is divided by 2.0 +- 1%.

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(BAT_SENSE, OUTPUT);
  Serial.begin(115200);
  pinMode(RLED, OUTPUT);
    
}

double ReadVoltage(byte  pin )
{
  double reading = analogRead( pin ) ; // Reference voltage is 3v3 so maximum reading is 3v3 = 4095 in range 0 to 4095
  if( reading < 1 || reading > 4095) {
    return 0 ;
   }
  // Return the voltage after fixin the ADC non-linearity
  return -0.000000000000016 * pow( reading, 4 ) + 0.000000000118171 * pow( reading, 3 )- 0.000000301211691 * pow( reading,2 )+ 0.001109019271794 * reading + 0.034143524634089 ;
} 

double x = 7600.0 ;
int i = 0 ;

void loop() {
  // Turning on the "Serial Plotter" tool shows the cell voltage as a graph
  digitalWrite(BAT_SENSE, HIGH);   // turn the Sense resistors on
  delay(10);  
  // wait for divider to settle to the cell voltage  
  if ( i++ >= 10 ){  // 10 step moving average filter
    x = 0.9*x + 200.0*ReadVoltage( ADC_Ch );
    Serial.println( x/2.0, 3 ) ;
   }
  else{  
    accumulate the first 10 readings to prevent huge exponential attack on the output.
    x = x + 200*ReadVoltage( ADC_Ch );
  }  
  digitalWrite(RLED, LOW);
  digitalWrite(BAT_SENSE, LOW);    // turn thesense resistors off by making the voltage LOW
  delay(250);
  digitalWrite(RLED,HIGH );
  delay(250);
}