How Many Watts Are You Using?

One of the best smart home hacks is implementing an energy monitor of some kind. It’s easy enough to say that you’re trying to save energy, but without the cold hard data, it’s just talk. Plus, it’s easy and a great way to build up something DIY that the whole family can use.

[Bogdan] built up a simple whole-apartment power monitor from scratch over the weekend, and he’s been nice enough to walk us through the whole procedure, starting with picking up a split-core CT sensor and ending up with a finished project.

The brains of his project are an ESP8266 module, which means that he needed to adapt the CT sensor to put out a voltage that lies within the chip’s ADC range of 0 V to 3.3 V. If you’re undertaking an energy monitor project, it’s as easy as picking the right burden resistor value and then shifting the ground-centered voltage up by 1.6 V or so. We say it’s easy, but it’s nice to have a worked example and some scope shots. The microcontroller reads the ADC frequently, does a little math, and you’re done.

The rest of the code was borrowed from here or there. EmonLib takes care of the math, ArduinoOTA allows him to reflash the firmware over the air, and Blynk takes care of making a nice Android app for visualization. In the end, a nice dot-matrix LED display lets [Bogdan] obsess about every last Watt in his living room. Adding a second ADC channel to the ESP8266 so that he can get a bit more accuracy out by measuring the instantaneous voltage is probably a project for next weekend.

Filed under: home hacks

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