Arduino Voltmeter Code

This arduino projects show how to make voltmeter with your arduino. It use voltage divider concept to estimate the voltage input.

Instruction;
1) Connect all jumper wire as shown in diagram.

Upload this code to your arduino

/*
  Voltmeter
  Voltmeter base on voltage divider concept.

  Code based on: http://www.clarenceho.net:8123/blog/articles/2009/05/17/arduino-test-voltmeter
  Coded by: arduinoprojects101.com
*/

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

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

// variables for input pin and control LED
  int analogInput = 1;
  float vout = 0.0;
  float vin = 0.0;
  float R1 = 50000.0;    // !! resistance of R1 !!
  float R2 = 4400.0;     // !! resistance of R2 !!

// variable to store the value 
  int value = 0;

void setup(){
  // declaration of pin modes
  pinMode(analogInput, INPUT);

  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  lcd.print("Vin=");
}

void loop(){
  // read the value on analog input
  value = analogRead(analogInput);

  vout = (value * 5.0) / 1024.0;
  vin = vout / (R2/(R1+R2));  

  // print result to lcd display
  lcd.setCursor(4, 0);
  lcd.print(vin);
  lcd.print("V");

  // sleep...
  delay(500);
}

Discussion;
a) You might saw some reading 0.06V even there is no Vin supply, this may caused by signal noise. You can add if statement to flush this reading. ie

if (vin<0.09) {
vin=0.0
}
add before print result to lcd display line.

For more detail: Arduino Voltmeter Code