tp-link Smart Plugs with Energy Monitoring

Several years ago I picked up a TP-Link HS110 switch so that I could turn lights on and off on a schedule. It had an interesting feature of being able to monitor energy usage as well.

The HS110 has an unfortunate design that covers the second socket in a wall outlet and makes it unusable. I purchased several HS105 units over time because two can be plugged into a standard outlet with the only drawback being the extra distance the normal plug extends from the wall. The HS105 was on sale as multipack on a somewhat regular basis. The drawback of the HS105 is that it doesn’t offer energy monitoring.

I came across the HS300 power strip that offers six switched outlets plus energy monitoring for each outlet. It has a flat angled plug, allowing two devices to fit in a standard wall outlet.

Each of these devices seems to be rated at 15A (1875W) total. That should be fine, since most of the standard wall plugs they would be plugged into aren’t rated for more than that, but it’s interesting that the current handling of the largest devices is the same as the smallest.

The energy monitoring was an interesting feature, and I was hoping to get around to doing more than glancing at it from my phone occasionally. Nearly three years after my first purchase I finally got around to writing a program to do what I wanted to log the energy usage.

I’d come across when I first bought the HS110, and thought I would get around to doing what I wanted quickly, but as with so many projects, it was set aside as less important. With the transient nature of the web, I’m glad that this site is still visible, and the resulting github repository tools proved invaluable for me getting my project working.

There are several python projects for communicating with these devices which I also found useful, but I was hoping to build a small program with very few dependencies. Part of what I wanted to know was the communication protocol over the ethernet, and that took the most time to decipher. is my project, with all of the work done in a single threaded C++ file. I’ll hopefully describe what I know of the protocol in the future. As it is, I’m pulling data from multiple devices and logging it using MRTG. I know there are significantly better graphics dashboards available, but this requires very little infrastructure, and I’m logging the raw data in case I ever really want to revisit it.

MRTG graph of AC Power Usage

For most people these devices connect to Alexa or Google Home and the scheduling plus voice controls are all that they will ever use.

I was very happy with having lamps set to turn on at sunset and turn off at specific times. The fact that I live at a latitude where sunset changes from after 9pm in the peak of summer to before 5pm midwinter was plenty for me. I also use them for controlling fans to adjust the climate in my home when I’m not relying on air conditioning.

From a system monitoring perspective I’ve considered having two Raspberry Pi, each plugged into a HS105, monitoring each other and power cycling the other device if it can’t be reached for a designated period of time.

Here are some of the other sites I found useful in getting to my current state:

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