Barebone Arduino LCD Voltmeter

A simple voltage divider(5:1 i.e. for 5 Volts of input the output should be 1 Volt) is used to Keep the measuring voltage range i.e 0-30 volt within Arduino's ADC input voltage range, i.e. 0-5 Volt. Another Resistance of 1 Ohm is used to drop the voltage across it, which is proportional to the current through it. This voltage across the 1 Ohm resistor is measured by the ADC of the Arduino.

(Note: This is not a very reliable setup, as the current is limited to a maximum of 5 Ampere Theoretically, however in practice if your ammeter will drop about 5 Volt then of course the voltage source won't be very helpful. But for the small current circuit, it can be implemented very well.

#include "LiquidCrystal.h"

LiquidCrystal lcd(6, 5, 7, 4, 3, 2);

int VoltMeterProbe = A4;
int AmmeterProbe = A5;

void setup() {
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("  Energy Meter  ");
  lcd.setCursor(0, 1);
  lcd.print("  by Debashish  ");
  delay(3000);
  lcd.clear();
}

void loop() {
  float VoltMeterReading = analogRead(VoltMeterProbe);
  delay(50);
  VoltMeterReading = analogRead(VoltMeterProbe);
  //float Voltage = map(VoltMeterReading, 0, 1023, 0.00, 20.20);
  float Voltage = mapfloat(VoltMeterReading, 0, 1023, 0.00, 20.20);

  float AmmeterReading = analogRead(AmmeterProbe);
  delay(50);
  AmmeterReading = analogRead(AmmeterProbe);

  //float Current = map(AmmeterReading, 0, 1023, 0, 5000);
  float Current = mapfloat(AmmeterReading, 0, 1023, 0, 5000);

  lcd.setCursor(0, 0);
  lcd.print("Volts: ");
  lcd.setCursor(7, 0);
  lcd.print("        ");
  lcd.setCursor(7, 0);
  lcd.print(Voltage);
  lcd.setCursor(14, 0);
  lcd.print("V");

  lcd.setCursor(0, 1);
  lcd.print("Amps: ");
  lcd.setCursor(6, 1);
  lcd.print("        ");
  lcd.setCursor(6, 1);
  lcd.print(Current);
  lcd.setCursor(14, 1);
  lcd.print("mA");

  delay(900);
}

//A floating Point Map function
float mapfloat(long x, long in_min, long in_max, long out_min, long out_max)
{
  return (float)(x - in_min) * (out_max - out_min) / (float)(in_max - in_min) + out_min;
}