battery.h

/*
 Battery.h - Battery library
 Copyright (c) 2014 Roberto Lo Giacco.
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU Lesser General Public License as 
 published by the Free Software Foundation, either version 3 of the 
 License, or (at your option) any later version.
 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef BATTERY_H_
#define BATTERY_H_

#include <Arduino.h>

typedef uint8_t(*mapFn_t)(uint16_t, uint16_t, uint16_t);

class Battery {
  public:
    /**
     * Creates an instance to monitor battery voltage and level.
     * Initialization parameters depend on battery type and configuration.
     *
     * @param minVoltage is the voltage, expressed in millivolts, corresponding to an empty battery
     * @param maxVoltage is the voltage, expressed in millivolts, corresponding to a full battery
     * @param sensePin is the analog pin used for sensing the battery voltage
     */
    Battery(uint16_t minVoltage, uint16_t maxVoltage, uint8_t sensePin);

    /**
     * Initializes the library by optionally setting additional parameters.
     * To obtain the best results use a calibrated reference using the VoltageReference library or equivalent.
     * 
     * @param refVoltage is the board reference voltage, expressed in millivolts
     * @param dividerRatio is the multiplier used to obtain the real battery voltage
     * @param mapFunction is a pointer to the function used to map the battery voltage to the remaining capacity percentage (defaults to linear mapping)
     */
    void begin(uint16_t refVoltage, float dividerRatio, mapFn_t = 0);

    /**
     * Enables on-demand activation of the sensing circuit to limit battery consumption.
     *
     * @param activationPin is the pin which will be turned HIGH or LOW before starting the battery sensing
     * @param activationMode is the optional value to set on the activationPin to enable battery sensing, defaults to LOW
     *            useful when using a resistor divider to save on battery consumption, but it can be changed to HIGH in case
     *            you are using a P-CH MOSFET or a PNP BJT
     */
    void onDemand(uint8_t activationPin, uint8_t activationMode = LOW);

    /**
     * Activation pin value disabling the on-demand feature.
     */
    static const uint8_t ON_DEMAND_DISABLE = 0xFF;

    /**
     * Returns the current battery level as a number between 0 and 100, with 0 indicating an empty battery and 100 a
     * full battery.
     */
    uint8_t level();
    uint8_t level(uint16_t voltage);

    /**
     * Returns the current battery voltage in millivolts.
     */
    uint16_t voltage();

  private:
    uint16_t refVoltage;
    uint16_t minVoltage;
    uint16_t maxVoltage;
    float dividerRatio;
    uint8_t sensePin;
    uint8_t activationPin;
    uint8_t activationMode;
    mapFn_t mapFunction;
};

//
// Plots of the functions below available at
// https://www.desmos.com/calculator/x0esk5bsrk
//

/**
 * Symmetric sigmoidal approximation
 * https://www.desmos.com/calculator/7m9lu26vpy
 *
 * c - c / (1 + k*x/v)^3
 */
static inline uint8_t sigmoidal(uint16_t voltage, uint16_t minVoltage, uint16_t maxVoltage) {
  // slow
  // uint8_t result = 110 - (110 / (1 + pow(1.468 * (voltage - minVoltage)/(maxVoltage - minVoltage), 6)));

  // steep
  // uint8_t result = 102 - (102 / (1 + pow(1.621 * (voltage - minVoltage)/(maxVoltage - minVoltage), 8.1)));

  // normal
  uint8_t result = 105 - (105 / (1 + pow(1.724 * (voltage - minVoltage)/(maxVoltage - minVoltage), 5.5)));
  return result >= 100 ? 100 : result;
}

/**
 * Asymmetric sigmoidal approximation
 * https://www.desmos.com/calculator/oyhpsu8jnw
 *
 * c - c / [1 + (k*x/v)^4.5]^3
 */
static inline uint8_t asigmoidal(uint16_t voltage, uint16_t minVoltage, uint16_t maxVoltage) {
  uint8_t result = 101 - (101 / pow(1 + pow(1.33 * (voltage - minVoltage)/(maxVoltage - minVoltage) ,4.5), 3));
  return result >= 100 ? 100 : result;
}

/**
 * Linear mapping
 * https://www.desmos.com/calculator/sowyhttjta
 *
 * x * 100 / v
 */
static inline uint8_t linear(uint16_t voltage, uint16_t minVoltage, uint16_t maxVoltage) {
  return (unsigned long)(voltage - minVoltage) * 100 / (maxVoltage - minVoltage);
}




#endif // BATTERY_H_