A class to Measure the Battery

[hlehoux]

Hi all, for the sake of beginners like myself and to get advice on it, here is the code i have done to measure the battery of my sensors

based on @sundberg84 here: EasyNewbie-PCB-for-MySensors and articles i've read here

Please provide advice on how to manage switching analogReference()

Here is the class definition:

class MyBM {
  public:
    MyBM();
    MyBM(const float _VMIN, const float _VMAX);
    void setup(void);
    void MeasureBattery(void); //The battery calculations
  private:
    void burnreadings(void);
    float VBAT_PER_BITS;
    float VMIN;                          //  Vmin (radio Min Volt)=1.9V (564v)
    float VMAX;                          //  Vmax = (2xAA bat)=3.0V (892v)
    int batteryPcnt = 0;                 // Calc value for battery %
    int batLoop = 0;                     // Loop to help calc average
    int batArray[3];                     // Array to store value for average calc.
    unsigned int BATTERY_SENSE_PIN = A0; // select the input pin for the battery sense point
    int sValue;
    float Vbat;
};

You can change the values in the constructor MyBM() ; by default it is the resistors 1M and 470k for EasyPCB.

Following advice found on stackoverflow, i make 8 readings in burnreadings() when switching from analogReference(INTERNAL) to analogReference(DEFAULT) back & forth

MyBM::MyBM() {
  this->VMIN= 2.0 ;                   //  Vmin (radio Min Volt)=1.9V (564v)
  this->VMAX= 3.3;                    //  Vmax = (2xAA bat)=3.0V (892v)
  this->VBAT_PER_BITS= (1470/470)*(1.1/1024);
}

MyBM::MyBM(const float _VMIN, const float _VMAX) {
  MyBM();
  this->VMIN= _VMIN;
  this->VMAX= _VMAX;
}

void MyBM::burnreadings(void)
{
  for (int i = 0; i < 8; i++)
  {
    analogRead(BATTERY_SENSE_PIN);
  }
}

void MyBM::setup(void) {
  //=========================
  // BATTERY MEASURER
  
  //DEFAULT: the default analog reference of 5 volts (on 5V Arduino boards) or 3.3 volts (on 3.3V Arduino boards)
  //INTERNAL: an built-in reference, equal to 1.1 volts on the ATmega168 or ATmega328 and 2.56 volts on the ATmega8 (not available on the Arduino Mega)
  //EXTERNAL: the voltage applied to the AREF pin (0 to 5V only) is used as the reference.

  analogReference(INTERNAL);    // set the ADC reference to 1.1V
  burnreadings();            // make 8 readings but don't use them
  delay(10);                    // idle some time
 
  //Battery inital calc
  DPR("With Battery VMax (100%) = "); DPR(VMAX); DPR("volts and Vmin (0%) = "); DPR(VMIN); DPRLN(" volts");
  DPR("Battery Percent 25%/50%/75% calculates to: "); DPR(((VMAX - VMIN) / 4) + VMIN); DPR("/"); DPR(((VMAX - VMIN) / 2) + VMIN); DPR("/"); DPRLN(VMAX - ((VMAX - VMIN) / 4));
  sValue = analogRead(BATTERY_SENSE_PIN);
  DPR("Batterysens :"); DPRLN(sValue);
  Vbat  = sValue * VBAT_PER_BITS;
  batteryPcnt = static_cast<int>(((Vbat - VMIN) / (VMAX - VMIN)) * 100.);
  DPR("Current battery are measured to (please confirm!): "); DPR(batteryPcnt); DPR(" % - Or "); DPRLN(Vbat); DPRLN(" Volts");

  analogReference(DEFAULT);     // set the ADC reference back to internal
  burnreadings();            // make 8 readings but don't use them
  delay(10);                    // idle again
  
  //=========================
}

void MyBM::MeasureBattery() {
  analogReference(INTERNAL);    // set the ADC reference to 1.1V
  burnreadings();            // make 8 readings but don't use them
  delay(10);                    // idle some time
 
  // Battery monitoring reading
  sValue = analogRead(BATTERY_SENSE_PIN);
  DPR("Batterysens :"); DPRLN(sValue);
  //delay(500);

  // Calculate the battery in %
  Vbat  = sValue * VBAT_PER_BITS;
  batteryPcnt = static_cast<int>(((Vbat - VMIN) / (VMAX - VMIN)) * 100.);

  DPR("Battery percent: "); DPR(batteryPcnt); DPR(" %"); DPR("Battery Voltage: "); DPR(Vbat); DPRLN(" Volts");
  
  // Add it to array so we get an average of 3 (3x20min)
  batArray[batLoop] = batteryPcnt;

  if (batLoop > 2) {
    batteryPcnt = (batArray[0] + batArray[1] + batArray[2]);
    batteryPcnt = batteryPcnt / 3;

    if (batteryPcnt > 100) {
      batteryPcnt = 100;
    }
    DPR("Battery Average (Send): "); DPR(batteryPcnt); DPRLN(" %");
    sendBatteryLevel(batteryPcnt);
    batLoop = 0;
  }
  else
  {
    batLoop++;
  }

  analogReference(DEFAULT);     // set the ADC reference back to internal
  burnreadings();            // make 8 readings but don't use them
  delay(10);                    // idle again
}

Here is how i use it with a sensor that manages both interrupts and a sensor-specific timeout

// sdj is an object representing the sensor
MyBM bm;

void setup()
{
  sdj.setup();
  bm.setup();
}

void loop()
{
  if (tripped==0) {   
    the_switch= sdj.get();
  } else if (tripped==MY_WAKE_UP_BY_TIMER) {
    if (sdj.wait_next()) {
      // timeout needs to do something for the sensor
      sdj.resetCode();
    } else {
    // timeout , nothing occured for sensor
    bm.MeasureBattery();
    }
  }
  
  // Sleep until something happens with the sensor or timeout
  tripped= sdj.sleep(WAIT_LOOP);
}