#include <Wire.h>                                               
#include <LiquidCrystal_I2C.h>                                  
LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);    
float H=0;                                                       
float U=0;

void setup()   
{Serial.begin(9600);                                          
analogReference(INTERNAL);
lcd.begin(16,2);                                               
pinMode(13, OUTPUT);                                            
}                                              

void loop()                                                     
{lcd.setCursor(0,0);                                           
lcd.print("Napeti:");                                           
lcd.setCursor(15,0);                                            
lcd.print("V");                                                
lcd.setCursor(9,0);                                             
H=analogRead(14);                                              
U=((H*20)/1023);                                              
lcd.print(U);                                                                                                       
delay(500);                                                     
if (U<10.5)                                                      
{lcd.setCursor(0,1);                                            
lcd.print("Baterie vybita!!");                                  
digitalWrite(13, HIGH);                                        
delay(1000);}                                                    
lcd.clear();                                                    
digitalWrite(13, LOW);                                        
}