user16946: How do we measure 100 Volts Arduino LCD Proje
#include <LiquidCrystal.h>
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
int analogInput = 0;
float vout = 0.0;
float vin = 0.0;
float R1 = 100000.0; // 100K ohm direnç
float R2 = 10000.0; // 10K ohm direnç
int value = 0;
void setup(){
   pinMode(analogInput, INPUT);
   lcd.begin(16, 2);
   lcd.print("DC VOLTMETRE-PROJEHOCAM");
}
void loop(){
   // read the value at analog input
   value = analogRead(analogInput);
   vout = (value * 5.0) / 1024.0; 
   vin = vout / (R2/(R1+R2)); 
   if (vin<0.09) {
   vin=0.0;
} 
lcd.setCursor(0, 1);
lcd.print("VOLTAJ V= ");
lcd.print(vin);
delay(500);
}


user6945: The project that you show as your reference : link in your question,  shows this picture :  
 
Change R1 to 200 K ohms.   The Arduino will receive 4.76 volts when the input is 100 volts.   
You will also need to change your program line for float R1 = 100000.0;
CAUTION :  Beware of high voltage.  Also, the Arduino is not isolated from the 100 volts. 

16946: <p>How do we measure 100 Volts Arduino LCD <a href="http://www.projehocam.com/arduino-lcd-voltmetre-yapimi/" rel="nofollow">Proje</a></p>

<pre><code>#include &lt;LiquidCrystal.h&gt;
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
int analogInput = 0;
float vout = 0.0;
float vin = 0.0;
float R1 = 100000.0; // 100K ohm direnç
float R2 = 10000.0; // 10K ohm direnç
int value = 0;
void setup(){
   pinMode(analogInput, INPUT);
   lcd.begin(16, 2);
   lcd.print("DC VOLTMETRE-PROJEHOCAM");
}
void loop(){
   // read the value at analog input
   value = analogRead(analogInput);
   vout = (value * 5.0) / 1024.0; 
   vin = vout / (R2/(R1+R2)); 
   if (vin&lt;0.09) {
   vin=0.0;
} 
lcd.setCursor(0, 1);
lcd.print("VOLTAJ V= ");
lcd.print(vin);
delay(500);
}
</code></pre>
 6945: <p>The project that you show as your reference : <a href="http://www.projehocam.com/arduino-lcd-voltmetre-yapimi/" rel="nofollow noreferrer">link in your question</a>,  shows this picture :  </p>

<p><a href="https://i.stack.imgur.com/5Dxpa.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5Dxpa.jpg" alt="enter image description here"></a>  </p>

<p>Change R1 to 200 K ohms.   The Arduino will receive 4.76 volts when the input is 100 volts.   </p>

<p>You will also need to change your program line for float R1 = 100000.0;</p>

<p><strong>CAUTION :  Beware of high voltage.  Also, the Arduino is not isolated from the 100 volts.</strong> </p>
