baterry-level-reader.ino

/*
 * AJ Alves (aj.alves@zerokol.com)
*/
#define BATERRY_LEVEL_IN A0 // Arduino analogic pin
#define ANALOGIC_RESOLUTION 1024 // The analogic board resolution, for example, Arduino Uno is 10 bit (from 0 to 1023)
#define REFERENCE_VOLTAGE 5.0 // The reference voltage, for example, Arduino Uno works in 5 V reference voltage by default
#define R1 3000000.0 // resistance of R1 (3 MR)
#define R2 1000000.0 // resistance of R2 (1 MR)
#define EXPECTED_V_OUT 12 // The intented voltage, 12 V

void setup() {
  Serial.begin(9600); // Setup Serial Port
}

void loop() {
  int value = analogRead(BATERRY_LEVEL_IN); // Read value at analog input
  float vOut = (value * REFERENCE_VOLTAGE) / ANALOGIC_RESOLUTION; // Calculate output voltage with rule of three formula
  float vIn = vOut / (R2 / (R1 + R2)); // Calculate input voltage with voltage divider formula
  int percent = vIn * 100 / EXPECTED_V_OUT; // Calculating baterry level percentage with rule of three formula
  Serial.print("Baterry level is: ");
  Serial.print(vIn);
  Serial.print("V (");
  Serial.print(percent);
  Serial.println("%);\n");
  delay(3000); // Wait 3 seconds
}