# Watts Up?

A project log for ESP8266 Current Monitor

Basic energy monitor using the ESP8266 and the ATMega328

Patrick McDonnell 01/07/2015 at 17:440 Comments

Today has already been a very good day for the energy monitor. I've got a very basic current sensing system running off of a basic circuit, and it seems to be within +/- 7% accuracy. Using an old set of christmas lights as a load, I was able to see the ac current fluctuate by 30mV, which equates out to 0.21A, or 24.8 watts, which is right around what google said is the wattage of a string of 50 lights.

Today I will be attempting to come up with a function that calculates the RMS amperage of the alternating current. I'll most likely be taking the average difference between the high and low voltages and calculating amperage that way.

The arduino and breadboard circuit, consisting of a 1k resistor, 4.7uf capacitor, and a 3.3v connection from the arduino board.

The CT sensor and festive holiday decorations made a perfect match. I needed something with separated live and neutral wires, and these fit the bill.

The raw analogRead values coming from the arduino. 688 - 655 = 33 * 4.8mv/unit = 0.15V /1000KΩ * 2000:1 CT ratio = 0.31A / sqrt(2) = 0.22 A * 120V = 26.4W! Math, dawg!

Stay tuned for more complex math and other fun things.