Ardu Voltmeter

#include <Wire.h>
#include <Adafruit_ADS1015.h>

int r1 = 20000;
int r2 = 5000;
float Voltage;
float supply;

Adafruit_ADS1115 ads;  /* Use this for the 16-bit version */
void setup(void)
{

  Serial.begin(9600);
  Serial.println("Hello!");

  Serial.println("Getting differential reading from AIN0 (P) and AIN1 (N)");
  Serial.println("ADC Range: +/- 6.144V (1 bit = 3mV/ADS1015, 0.1875mV/ADS1115)");

  // ads.setGain(GAIN_TWOTHIRDS);  // 2/3x gain +/- 6.144V  1 bit = 3mV      0.1875mV (default)


  ads.begin();
}

void loop(void)
{
  float results;
  float multiplier = 0.1875F; /* ADS1115  @ +/- 6.144V gain (16-bit results) */

  results = ads.readADC_Differential_0_1();
  Voltage = results * multiplier;
  supply = (Voltage*(r1+r2))/r2;

  Serial.print("Differential: ");
  Serial.print(results);
  Serial.print("(");
  Serial.print(Voltage);
  Serial.println("mV)");
  Serial.println(supply);

  delay(2000);
}