# How to build an Arduino energy monitor – measuring mains voltage and current

This guide details how to build a simple electricity energy monitor on that can be used to measure how much electrical energy you use in your home. It measures voltage with an AC to AC power adapter and current with a clip on CT sensor, making the setup quite safe as no high voltage work is needed.

The energy monitor can calculate real power, apparent power, power factor, rms voltage, rms current. All the calculations are done in the digital domain on an Arduino.

### Step One – Gather Components

You will need:

1x Arduino

Voltage sensing electronics:

1x 9V AC-AC Power Adapter

1x 100kOhm resistor for step down voltage divider.

1x 10kOhm resistor for step down voltage divider.

2x 470kOhm (for voltage divider, any matching value resistor pair down to 10K)

1x 10uF capacitor

Current sensing electronics

1x CT sensor SCT-013-000

1x Burden resistor 18 Ohms if supply voltage is 3.3V or 33 Ohms if supply voltage is 5V.

2x 470kOhm (for voltage divider, any matching value resistor pair down to 10K)

1x 10uF capacitor

Other

1x A breadboard and some single core wire.

Oomlout do a good arduino + breadboard bundle here £29

### Step Two – Assemble the electronics

The electronics consist of the sensors (which produce signals proportional to the mains voltage and current) and the sensor electronics that convert these signals into a form the Arduino is happy with.

#include “EmonLib.h”             // Include Emon Library
EnergyMonitor emon1;             // Create an instance

void setup()
{
Serial.begin(9600);

emon1.voltage(2, 234.26, 1.7);  // Voltage: input pin, calibration, phase_shift
emon1.current(1, 111.1);       // Current: input pin, calibration.}

void loop() {  emon1.calcVI(20,2000);         // Calculate all. No.of wavelengths, time-out
emon1.serialprint();           // Print out all variables}

For more detail:  How to build an Arduino energy monitor – measuring mains voltage and current

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