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Hi folks,

Here is a shot at getting some battery information using only the voltage divider - which is all I have implemented so far.

Comments, criticism, hints, more than welcome.

Thanks in advance.

Andrew.

/*
** Andrew Scott Solar Monitor 11-Sept-2012
*/

// libraries
#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>

// Define LCD I2C address and pins
#define I2C_ADDR    0x3F
#define BACKLIGHT_PIN     3
#define En_pin  2
#define Rw_pin  1
#define Rs_pin  0
#define D4_pin  4
#define D5_pin  5
#define D6_pin  6
#define D7_pin  7

// For LCD healthcheck. LCD sometimes seems to freeze. This 
// seems to be a problem after uploading code and rebooting 
// when running from USB power only. 
boolean lcdHealthCheck = false;


// Setup LCD
LiquidCrystal_I2C       lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);

void setup()
{

  // Initialize LCD
  lcd.begin (20,4);

  // Switch on LCD the backlight
  lcd.setBacklightPin(BACKLIGHT_PIN,POSITIVE);
  lcd.setBacklight(HIGH);

  // Static LCD characters
  lcd.setCursor ( 0, 0 );
  lcd.print("BATT: ");
  lcd.setCursor ( 11, 0 );
  lcd.print("V");

}

void loop(){

  // ADC value from voltage divider
  // R1 = 10K, R2 = 1K, resolution 0.05V
  int battVRaw;

  // Lazy division on the ADC value, matches DMM
  float battDivideBy = 18.45;

  // Actual voltage
  float battVActual;

  // Value for making battery charge bar
  float chargeBar;

  // Read A2 to get ADC value for battery voltage
  battVRaw = analogRead(A2);

  // Do lazy maths to calculate actual battery voltage
  battVActual = (battVRaw / battDivideBy);

  // Print actual battery voltage
  lcd.setCursor ( 6, 0);
  lcd.print(battVActual);

  // Print ADC value for debugging - temporary
  lcd.setCursor ( 13, 0 );
  lcd.print("A2: ");
  lcd.print(battVRaw);

  // Print charge status, or battery level if not charging
  
  // Position cursor at 3rd line, 5th char from left.
  lcd.setCursor ( 4, 2 );
  
  // If voltage < 13.19, probably not charging
  // This should probably be verified by checking solar current
  // sensor when installed. 
  //
  // DMM shows 13V stable when full, and inverter auto shutdown
  // happens at < 12V, so that can be minimum for now. 
  // A nice easy 10 segment bar graph.
  
  if(battVActual < 13.19){
    lcd.print("E");
    chargeBar = 12.0;
    while(chargeBar < battVActual){
      lcd.print(char(255));
      chargeBar = chargeBar + 0.1;
    }
    lcd.setCursor ( 14, 2);
    lcd.print("F");
  }  
  
  // Print charge status, cover all cases above 13.19V
  // Measurement accuracy seems good enough to identify these states
  // May require tweaking!
  
  else if(battVActual > 13.19 & battVActual < 13.81){
    lcd.print("FLOAT CHARGING");
  }
  else if(battVActual > 13.81 & battVActual < 14.39){   
    lcd.print("ABOVE FLOAT CHG.");
  }
  else if(battVActual > 14.39 & battVActual < 14.41){
    lcd.print("BOOST CHARGING");
  }
  else if(battVActual > 14.41 & battVActual < 14.59){
    lcd.print("ABOVE BOOST CHG.");
  }
  else if(battVActual > 14.59 & battVActual < 14.61){
    lcd.print("EQUALIZE CHARGE");
  }  
  else if(battVActual > 14.61){
    lcd.print("CHG. OVER VOLT!");
 
  }

  // Blinking star in the bottom right corner
  // for LCD health check
  lcd.setCursor ( 19, 3 );
  if(lcdHealthCheck == false){
    lcdHealthCheck = true;
    lcd.print("*");
  }else{
    lcdHealthCheck = false;
    lcd.print(" ");
  }

delay(2000);
}