i'm doing voltage indicator but the input voltage is different from output voltage show on lcd display. can someone help me how to solve the problem?

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 6, A0, A1, A2, A3);

int analogPin = A4;
float vout = 0.0;
float vin = 0.0;
float R1 = 100000.0; // resistance of R1 (100K)
float R2 = 10000.0; // resistance of R2 (10K)
int value = 0;
int a[5] = {};

int greenLed = 10;
int blueLed = 11;
int yellowLed = 12;
int redLed = 13;
int sound = 8;

void setup()
{
  pinMode(greenLed, OUTPUT);
  pinMode(blueLed, OUTPUT);
  pinMode(yellowLed,OUTPUT);
  pinMode(redLed,OUTPUT);
 
  pinMode(A0,OUTPUT);
  pinMode(A1,OUTPUT);
  pinMode(A2,OUTPUT);
  pinMode(A3,OUTPUT);
 
  pinMode(A4,INPUT);
 
  Serial.begin(9600);
  lcd.begin(16, 2);
  lcd.setCursor(1, 0);
  lcd.print("VOLT INDICATOR");
  lcd.setCursor(6, 1);
  lcd.print("BLIS");
  delay(3000);
  lcd.clear();
}

void loop()
{
 // LCD DISPLAY
 
 lcd.print("Voltage Level");
 // read the value at analog input
 value = analogRead(A4);
 vout = (value * 5) / 1024.0;
 vin = vout / (R2 / (R1 + R2));
 Serial.println (vin);
 
 if (vin < 0.09)
 {
  vin = 0.0;
 }
 
 lcd.setCursor(0, 1);
 lcd.print("Voltage V :");
 lcd.print(vin);
 delay(3000);
 //lcd.clear();
 
// LED & BUZZER
 
if(vin <= 11.3)
{
 digitalWrite(redLed, HIGH);
 //delay (1000);
 tone(sound, 1000, 250);             
 delay(1000);                             
 digitalWrite(redLed, LOW);
 //delay (1000);
 tone(sound, 2000, 250);             
 delay(1000);                               
}
 
  if(vin <= 11.60 && vin > 11.3)
{
 digitalWrite(greenLed,LOW);
 digitalWrite(blueLed,LOW);
 digitalWrite(yellowLed,HIGH);
 digitalWrite(redLed,HIGH);
}
 
  if(vin <= 12.1 && vin > 11.6)
{
  digitalWrite(greenLed,LOW);
  digitalWrite(blueLed,HIGH);
  digitalWrite(yellowLed,HIGH);
  digitalWrite(redLed,HIGH);
}

if(vin > 12.1)
{
  digitalWrite(greenLed,HIGH);
  digitalWrite(blueLed,HIGH);
  digitalWrite(yellowLed,HIGH);
  digitalWrite(redLed,HIGH);
}
}

 

Welcome to AAC!

the input voltage is different from output voltage show on lcd display

By how much do they differ?
Is the difference a constant percentage of the correct value?

 

. . .
value = analogRead(A4);
// donno if theres any help but you can try
vout = 2.5/512;
vout = vout*value;
// vout = (value * 5) / 1024.0;
// vin = vout / (R2 / (R1 + R2));
vin = vout * (R1/R2 + 1);
Serial.println (vin); // ? sending floating point value over serial . . . good question is -- what is been sent ?
. . .
lcd.setCursor(0, 1);
lcd.print("Voltage V :");
lcd.print(vin); // ? does the lcd.print() detect the float and convert it to anything reasonable display value . . . ?
. . .

 

Can you supply a schematic of the external wiring to the Nano?

I’m trying to figure out how you are using R1 & R2?