Practical case: solar battery monitor, Arduino UNO

#include <LiquidCrystal.h>

// LCD pins: RS, E, D4, D5, D6, D7
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

// Analog pins
const uint8_t PIN_BATTERY = A0;
const uint8_t PIN_CURRENT = A1;

// ADC reference
const float ADC_REF_VOLTAGE = 5.0;
const int ADC_MAX = 1023;

// Voltage divider values
const float R1 = 47000.0; // ohms, top resistor
const float R2 = 10000.0; // ohms, bottom resistor

// ACS712 settings
// Set according to your module:
// 5A module  -> 185.0 mV/A
// 20A module -> 100.0 mV/A
// 30A module -> 66.0  mV/A
const float ACS712_MV_PER_AMP = 185.0;

// Calibration values
float currentZeroVoltage = 2.50;   // Will be refined during startup calibration
float voltageCalibrationFactor = 1.000; // Adjust after comparing to multimeter if needed
float currentCalibrationFactor = 1.000; // Adjust after comparing to multimeter if needed

// Sampling
const int NUM_SAMPLES_VOLTAGE = 20;
const int NUM_SAMPLES_CURRENT = 100;

// Timing
unsigned long lastDisplayUpdate = 0;
const unsigned long DISPLAY_INTERVAL_MS = 500;

// Optional status thresholds
const float LOW_BATTERY_VOLTAGE = 11.8;
const float IDLE_CURRENT_THRESHOLD = 0.08;

float readAverageVoltageAtPin(uint8_t pin, int samples) {
  long sum = 0;
  for (int i = 0; i < samples; i++) {
    sum += analogRead(pin);
    delay(2);
  }
  float adc = sum / (float)samples;
  return (adc * ADC_REF_VOLTAGE) / ADC_MAX;
}

float readBatteryVoltage() {
  float dividedVoltage = readAverageVoltageAtPin(PIN_BATTERY, NUM_SAMPLES_VOLTAGE);
  float batteryVoltage = dividedVoltage * ((R1 + R2) / R2);
  batteryVoltage *= voltageCalibrationFactor;
  return batteryVoltage;
}

float readCurrent() {
  float sensorVoltage = readAverageVoltageAtPin(PIN_CURRENT, NUM_SAMPLES_CURRENT);
  float deltaVoltage = sensorVoltage - currentZeroVoltage; // volts
  float current = (deltaVoltage * 1000.0) / ACS712_MV_PER_AMP; // amps
  current *= currentCalibrationFactor;
  return current;
}

void calibrateCurrentZero() {
  // Assumes no current is flowing through ACS712 during startup.
  float total = 0.0;
  const int rounds = 10;
  for (int i = 0; i < rounds; i++) {
    total += readAverageVoltageAtPin(PIN_CURRENT, 50);
    delay(20);
  }
  currentZeroVoltage = total / rounds;
}

const char* stateText(float current, float batteryVoltage) {
  if (current > IDLE_CURRENT_THRESHOLD) {
    return "CHARGING";
  } else if (current < -IDLE_CURRENT_THRESHOLD) {
    return "DISCHARGE";
  } else if (batteryVoltage < LOW_BATTERY_VOLTAGE) {
    return "LOW BAT";
  } else {
    return "IDLE";
  }
}

void printPadded(String text, uint8_t width) {
  if (text.length() >= width) {
    lcd.print(text.substring(0, width));
  } else {
    lcd.print(text);
    for (uint8_t i = text.length(); i < width; i++) {
      lcd.print(' ');
    }
  }
}

void setup() {
  lcd.begin(16, 2);
  Serial.begin(9600);

  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Solar Battery");
  lcd.setCursor(0, 1);
  lcd.print("Monitor Start");
  delay(1200);

  calibrateCurrentZero();

  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Zero I V=");
  lcd.print(currentZeroVoltage, 3);
  delay(1500);

  Serial.println("solar-battery-lcd-monitor");
  Serial.print("Current zero voltage = ");
  Serial.println(currentZeroVoltage, 4);
}

void loop() {
  if (millis() - lastDisplayUpdate >= DISPLAY_INTERVAL_MS) {
    lastDisplayUpdate = millis();

    float batteryVoltage = readBatteryVoltage();
    float current = readCurrent();
    float power = batteryVoltage * current;
    const char* state = stateText(current, batteryVoltage);

    // LCD line 1: Voltage and current
    lcd.setCursor(0, 0);
    String line1 = "V:";
    line1 += String(batteryVoltage, 2);
    line1 += " I:";
    line1 += String(current, 2);
    printPadded(line1, 16);

    // LCD line 2: Power and state
    lcd.setCursor(0, 1);
    String line2 = "P:";
    line2 += String(power, 1);
    line2 += " ";
    line2 += state;
    printPadded(line2, 16);

    // Serial output for validation
    Serial.print("Battery_V=");
    Serial.print(batteryVoltage, 3);
    Serial.print(", Current_A=");
    Serial.print(current, 3);
    Serial.print(", Power_W=");
    Serial.print(power, 3);
    Serial.print(", State=");
    Serial.println(state);
  }
}