My buddy Frank (the guy talking way too fast above) and I designed an open source energy meter. It is still in early beta, but Frank’s about to be commissioned in the Navy, and I have a three month Merchant Marine cruise coming up, so neither of us will have time to work on it for a while. Anyways, it’s pretty awesome if I do say so myself. It’s similar to the Kill A Watt, but it’s wireless, uses mesh networking, and is scalable from a metering a single outlet to service as building’s primary energy meter.
Features
- Uses current transformer for shuntless current measurements
- Wireless (ZigBee)
- True RMS voltage and current measurements, for accurate readings with noisy loads
- Power factor calculated with Fast Fourier Transform, with possibility of using FFT for Total Harmonic Distortion calculation
- 8 core Propeller microcontroller running at 80 MHz allows for lots of number crunching
Also, I wrote an OS X Cocoa application for an interface to sensors. Currently, it only recognizes one sensor, but with a little modification I’ll make it handle any number of sensors. We even configured the sensors to occasionally send current and voltage waveforms. That’s mostly eye-candy, but could be useful to a utility to identify problems or particularly noisy loads.
;)
TODO
- Design a board that fits a standard size box
- Add the ability to switch out current transformer’s burden resistance on the fly, depending on amperage, to allow for a wider range of current. Currently we’re getting accurate measurements from 10 mA to about 12 A, after that it starts clipping at the input of the op amp. For a house, there’s a much wider range of currents.
- Find wireless modules that allow for huge mesh networks. Big enough for all the houses in a small town to pass occasional readings to the utility.
If you’re interested in getting involved, let us know. You can check out the live code at our Google Code page.
Downloads
Design Summary from APPA Conference