All posts by scruss

The Yonge & St Clair Autoharp Guy

This guy sets up on the SE corner of Yonge & St Clair most afternoons, and plays endless variations on the above recording. He’s playing an autoharp with the chord bars removed, and run through a homebrew battery-powered amplifier with much reverb and distortion. A bunch of the burbly noises are 8kbit/s voice recorder artifacts from my phone.

Although the themes seem repetitive, I don’t think they repeat exactly every time. He seems to be in a happy place playing them.

Log your electricity consumption with Powermon433

NB: this is in the  early stages of development, but does work. It’s by no means a plug-and-play solution. You’re going to have to do some coding, and perhaps some soldering. Undaunted? Read on …

I really like the Blue Line Innovations PowerCost Monitor™ (aka the Black & Decker Power Monitor EM100B). I bought one long before the OPA started to give them away free to Ontario households as part of their peaksaver PLUS program. It’s a little device that clamps to your hydro meter and sends instantaneous power readings to a display.

PowerMonitor-displays
Power Monitor displays — Black & Decker on the left, Blueline on the right

Wouldn’t it be so much better if you could log and analyze these data? So a day’s power consumption might graph to something like this:

PowerMonitor-20140929Yup, this is my real electricity consumption, as logged from the PowerCost Monitor. You can see the fridge cycling on and off, and I think the big mid-day spike was either the AC or the dryer; someone was home on that Monday. The rather blocky green line is Toronto Hydro’s hourly smart meter data. It really hasn’t got the resolution to show really detailed power use.

That spike at 06:30; what’s that? Let’s take a look:

PowerMonitor-20140929-kettleThat’s me boiling the kettle. You can see that the time resolution is better than a minute, and the power is to the watt. Mmm, coffee …

All of this is recorded using a simple Arduino-based solution, originally cooked up by Bryan Mayland. I’ve forked his code and added some instructions: scruss/Powermon433. Here’s the rig I’ve been using to log data over a USB serial link:

Arduino FIO compatible + RFM69W board + FTDI serial
Arduino FIO compatible + RFM69W board + FTDI serial

That’s a particularly ugly rig, due to the limitations of the 3.3 V receiver board I was using. There are other options that work with more normal Arduino boards up on github.

Here’s a sample of the data I’m logging, including the kettle incident:

Datetime Elapsed_s Energy_Wh Power_W Temp_C
2014-09-29T06:27:44 23241.7 25876 289 15
2014-09-29T06:28:16 23273.6 25876 290 15
2014-09-29T06:28:48 23305.5 25876 291 15
2014-09-29T06:29:20 23337.4 25892 294 15
2014-09-29T06:29:52 23369.2 25892 286 15
2014-09-29T06:30:24 23401.1 25892 277 15
2014-09-29T06:30:56 23433.0 25892 357 15
2014-09-29T06:31:28 23464.9 25892 1844 15
2014-09-29T06:32:00 23496.8 25892 1836 15
2014-09-29T06:32:31 23528.5 25952 1829 15
2014-09-29T06:33:03 23560.2 25952 1818 15
2014-09-29T06:33:35 23592.1 25952 1836 15
2014-09-29T06:34:07 23624.0 25952 1836 15
2014-09-29T06:34:39 23655.8 25952 1836 15
2014-09-29T06:35:11 23687.7 25952 1848 15
2014-09-29T06:35:43 23719.6 26048 1832 15
2014-09-29T06:36:15 23751.5 26048 2000 15
2014-09-29T06:36:46 23783.4 26048 2000 15
2014-09-29T06:37:18 23815.2 26048 2000 15
2014-09-29T06:37:50 23846.9 26048 368 15

You’ll see that I’m recording:

  • a system timestamp
  • the elapsed logging time, from the Arduino’s clock
  • instantaneous meter readings in watt-hours. Note that not every row has an update
  • the average power since the last record. The product of this and the time between records adds up to the energy consumption
  • the outside temperature in °C. This is not very accurate (in full sun it over-reads vastly) but better than nothing.

Compare that to the smart meter data:

DateTime Hour KwhUsage Cost Rate
2014-09-29 05:00:00 5 0.29 $0.02 $0.075
2014-09-29 06:00:00 6 0.31 $0.02 $0.075
2014-09-29 07:00:00 7 0.59 $0.04 $0.075

Not much data there, is there? Certainly not enough resolution to tell if a kettle has been running.

Even though this interface is homebrew and cheap, it is accurate. Here’s how four days of continuous readings stack up against Toronto Hydro’s meter:

  Power Monitor ndToronto Hydro Smart Meter
Day First Reading / Wh Last Reading / Wh Total Consumption / kWh No of readings Daily Total / kWh No of readings
2014-09-29 23896 43668 19.772 2711 19.77 24
2014-09-30 43668 52500 8.832 2710 8.82 24
2014-10-01 52500 68004 15.504 2711 15.51 24
2014-10-02 68004 81996 13.992 2712 13.99 24

The difference looks to me like aliasing; THES’s reporting is much more granular.

I’m going to develop this further to turn it into an easy (or at least, easier) to use logging platform. It’s taken us a few years to get here, but there’s nothing quite like a project finally working!