A Flash in the Meter Box

Dennis Smith

Issue 8, February 2018

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Concerned about the impact of a new air conditioner on his energy bills, Dennis found a genius way to keep track of power consumption.

Even for those of us who know electronics, the lack of authority to deal with anything inside the meter box leaves it much of a mystery regarding exactly what goes on inside. For safety (and legality) we don’t want to touch it, but Dennis created a great hack to take readings from his household energy meter.

Your device is a great, no-contact method of tracking energy usage. What made you embark on this project?

I was doing some painting in the house and needed to turn off the power so I could safely paint around a power point, when I noticed a red light pulsing on the meter box. I wondered what it was and so decided to Google it. At first I thought it was a coded series of rapid pulses, used to perform an electronic read of total energy consumed, but it turns out that most meters put out a single pulse for every Watt Hour of electricity as its consumed. I thought it would assist with monitoring electricity usage, as I had just purchased an air conditioner and was feeling nervous about the bill.

"Mr Google told me all I needed to know."

Did you have a working knowledge of electricity meters that you could bring to this project, or did you have to research things first?

I have an extensive background in electricity and electronics (45 years as a computer mainframe engineer) but no first-hand experience with electricity meters. Mr Google told me all I needed to know.

It’s always good when a little homework is all it takes! Did you have immediate success with your photo diode circuit, or did you need to make some modifications along the way?

The photo diode circuit was the tricky part and is still not as good as I would like it. I found the difficulty is in balancing sensitivity with immunity against ambient light changes. The pulses from the meter are in the visible spectrum, not infrared, so I had to use a BPW34 instead of an IR photo diode.

That’s a challenge, but nothing some light-proofing couldn’t assist with. Counting pulses is a great no-contact method to capture the data. Are there any caveats to this method that you’ve identified?

Only missed or false triggering causing the count to be wrong. Taping the photo cell to the meter box’s LED and covering it to block out light helps, but I have yet to find out what the electricity company think about that option! It’s not tampering with the equipment so should be okay, unless you get a disagreeable meter reader, of course!

Yes, there’s a fine line there for sure. Is this your first ESP8266 project?

Yes, it’s my first major project, but I have been playing around with the ESP8266 and the ESP32 for a little while now.

They’re a great piece of hardware, that’s for sure! Have you qualified the accuracy of the data logging? How does it compare to your energy bill’s assessment?

The accuracy is spot on, since the pulse is also used to step the meter’s mechanical counters, just so long as no false triggering occurs, as previously mentioned.


Solar charging is a nice potential upgrade. How are you powering the system right now?

Just batteries. Three Li-Ion cells in parallel will last around two weeks and are easily charged, though a solar charger could reduce the need for multiple cells in parallel.

Sounds simple enough! We’ve seen a few GPO outlets in power boxes, but they don’t seem to be terribly common, so batteries work! What would you change if creating the circuit from scratch a second time around?

I would design a PCB and encapsulate the hardware, potted to keep out moisture. Software updates can now be done over WiFi, so I’d look for Arduino Over The Air (OTA) programming. I have included code to do this, so removing the unit to perform software updates is not necessary.

Oh that’s a valid point - moisture is bound to end up inside the power box at some point, and OTA updates is always awesome! What other exciting project are you working on at the moment?

I’m in the process of renovating a house and intend to replace all 230V lighting with 12V LEDs that are powered by batteries, which are charged by solar panels. I’ll be using remote WiFi-controlled switches based on the ESP8266 and connected via MQTT. Sonoff (look on eBay) produce very nice touch-sensitive 230V switches, which are easily modified to run off 12V, and they use ESP8266 for the smarts.

Interesting - there’s definitely some amazing things that can be done with that! Thanks for taking us through your energy meter project, Dennis.

Dennis Smith

Dennis Smith

Retired Computer Mainframe Engineer.