#include <Wire.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_GFX.h>
#define OLED_ADDR   0x3C
Adafruit_SSD1306 display(-1);  // -1 = no reset pin
float Vin=0,Vout=0;
float R1 = 10000;              // R1 = 10K ohm                                       
float R2 = 1000;               // R2 =  1K ohm 
void setup()
{
  
display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR);
display.clearDisplay();
display.display();
Serial.begin(9600);
}

void loop() 
{
  
float A=analogRead(A0);       //read from A0
Vout = A*(5.0/1024.0);        //convert into voltage
Vin = Vout*((R1+R2)/R2);      //voltage divider equation 
Serial.print("A= ");
Serial.print(A);              //Serial print ADC value
Serial.print(" Vout ");
Serial.print(Vout);           //Serial print arduino input (voltage divider out put)voltage
Serial.print(" Vin ");
Serial.println(Vin);          //Serial print voltage divider input voltage(Supply voltage)
display.clearDisplay();
display.setTextSize(2);
display.setTextColor(WHITE);
display.setCursor(10,10);
display.print(Vin,3);         // display Supply voltage on OLED
display.print(" V");
display.display();
delay(1000);
}