Simple Arduino Battery Capacity Tester

/*
 * Li-Ion capacity tester.
 * set up:
 * 8 Ohm discharge load
 * ~190mA discharge rate.
 * I2C LCD.
 * MOSFET for discharge control.
 * 
 * software from e-battle.blogspot.com
 *
 * SCl pin = A5
 * SDA pin = A4
 *
 */


#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

//LCD set-up
LiquidCrystal_I2C lcd(0x27,20,4);  // set the LCD address to 0x27 for a 20 chars and 4 line lcd

// definitions

#define STATE_WAITING 0
#define STATE_MEASURING 1
#define STATE_MEASURING_ENDED 2
#define BAT_LI 0
#define BAT_NI 1
#define BAT_UNREC 2
#define BAT_LI_DISCHARGED 3

//variables

float vtgBatLoaded; //shows the drop in cell V under load
float vtgBatUnloaded; //cell V for no load
float vtgLoad;
float vtgDropOnLoad;
float vtgDropRin; 
float rLoad=8; //resistanse of the load in Ohms
float rIn; //calculated cell internal resistance
float batCurrent;
float mAh; //running total cell capacity
uint8_t FET_Base=7; //otherwise known as the Gate.
uint8_t button = 6; 
uint8_t speaker= 5;
uint8_t state=STATE_WAITING;
float LiChargedVtg=4.35;
float LiCutoffVtg=2.9;
float NiChargedVtg=1.45;  
float NiCutoffVtg=1.1;
float cutoff;
uint8_t BatteryType;
boolean DischargeAllowed=false;
String BatTypeString;

void setup()
{
  pinMode(FET_Base,OUTPUT);
  pinMode(button,INPUT); //can be changed in the circuit to active low,
                         // will need to turn on the internal pull-up
  pinMode(speaker,OUTPUT);
  digitalWrite(FET_Base,LOW);
  noTone(speaker);
  lcd.init();
  lcd.backlight();
}

void loop()
{
   if (state==STATE_MEASURING)
   {
  
  vtgBatUnloaded=analogRead(0)*5.0/1024.0; //get the voltage of UNLOADED battery
  
  if (vtgBatUnloaded<cutoff)
  {
    state=STATE_MEASURING_ENDED;
    DischargeAllowed=false;
    for (uint8_t i=0;i<4;++i)
    {tone(speaker,2000,500); delay(500);noTone(5);delay(300);}
  }
  digitalWrite(FET_Base,HIGH); //turn the MOSFET on
  delay(1000);
  vtgBatLoaded=analogRead(0)*5.0/1024.0;   //get the voltage of LOADED battery
  vtgLoad=analogRead(1)*5.0/1024.0;
  digitalWrite(FET_Base,LOW);//turn the MOSFET off
  vtgDropOnLoad=vtgBatLoaded-vtgLoad;
  if(vtgDropOnLoad>0) batCurrent=vtgDropOnLoad/rLoad;
   else batCurrent=0;
  vtgDropRin=vtgBatUnloaded-vtgBatLoaded;
  if(batCurrent>0) rIn=vtgDropRin/batCurrent;
  else rIn=0;
  mAh+=batCurrent/3.6; //*1000.0/3600.0;
  lcd.clear();
  lcdState();
    lcd.setCursor(0,0);
    lcd.print(" Bat   Load    I ");
  lcd.setCursor(0,1);
  lcd.print(vtgBatUnloaded); lcd.print("V  ");lcd.print(vtgBatLoaded); lcd.print("V  ");lcd.print(batCurrent); lcd.print("A");
  lcd.setCursor(0,2);
  lcd.print("Rin= "); lcd.print(rIn); lcd.setCursor(11,2); lcd.print(" Ohm");
  lcd.setCursor(0,3);
  lcd.print("Cap= "); lcd.print(mAh); lcd.print(" mA/h"); 
  delay(500);
   } 
   else if (state==STATE_WAITING)
   {
     digitalWrite(FET_Base,LOW);//turn the MOSFET off
     vtgBatUnloaded=analogRead(0)*5.0/1024.0; //get the voltage of UNLOADED battery
     DefBatteryType();
     lcd.clear();
     lcdState();
     lcd.setCursor(0,0);
     lcd.print("Bat= "); lcd.print(vtgBatUnloaded); lcd.print(" V");
     lcd.setCursor(0,1);
     lcd.print(BatTypeString);
     lcd.setCursor(0,2);
     lcd.print("Test ");
     if (DischargeAllowed) lcd.print("allowed");
     else lcd.print("denied");
     CheckButtons();
     delay(500);
   }
   else if (state==STATE_MEASURING_ENDED)
   {
     digitalWrite(FET_Base,LOW);//turn the MOSFET off
     vtgBatUnloaded=analogRead(0)*5.0/1024.0; //get the voltage of UNLOADED battery
     lcd.clear();
     lcdState();
     lcd.setCursor(0,0);
     lcd.print("Bat= "); lcd.print(vtgBatUnloaded); lcd.print(" V");
     lcd.setCursor(0,1);
     lcd.print("Cap= ");lcd.print(mAh); lcd.print(" mA/h");     
     CheckButtons();
     delay(500);
   }
}

void CheckButtons(void) {
   
   if (digitalRead(button)==HIGH){ // if changed to active low.....you know what to do!
    switch (state){
      
    case STATE_WAITING : DefBatteryType();
    if (DischargeAllowed){ mAh=0; state=STATE_MEASURING;
    tone(speaker,1000,500); delay(500);noTone(5);}
    break;
    
    case STATE_MEASURING : state=STATE_MEASURING_ENDED;
    break;
    
    case STATE_MEASURING_ENDED : state=STATE_WAITING;
    break;
   }
 }
 }


void lcdState(void){
   String stateString;
   lcd.setCursor(0,0);
   if(state==STATE_WAITING) stateString="Waiting       ";
   if(state==STATE_MEASURING) stateString="Measuring     ";
   if(state==STATE_MEASURING_ENDED) stateString="Measuring done";
   lcd.print(stateString);
 }
    
void DefBatteryType(void){
   
       if (vtgBatUnloaded>LiCutoffVtg&&vtgBatUnloaded<LiChargedVtg)
       {BatteryType=BAT_LI; DischargeAllowed=true;BatTypeString="Li-ion battery";cutoff=LiCutoffVtg;}
       if (vtgBatUnloaded>NiCutoffVtg&&vtgBatUnloaded<NiChargedVtg)
       {BatteryType=BAT_NI; DischargeAllowed=true;BatTypeString="Ni-MH battery ";cutoff=NiCutoffVtg;}
       if (vtgBatUnloaded<LiCutoffVtg&&vtgBatUnloaded>NiChargedVtg)
       {BatteryType=BAT_LI_DISCHARGED; DischargeAllowed=false;BatTypeString="Li-ion battery";}
       if (vtgBatUnloaded<NiCutoffVtg||vtgBatUnloaded>LiChargedVtg)
       {BatteryType=BAT_UNREC; DischargeAllowed=false;BatTypeString="UNKNOWN bat   ";}
 }