MPGuino-style open source kill-a-watt meter?

[Thalass]

Hey folks. I've been keeping an eye on the mpguino over at ecomodder for a while now. And i've been looking for something similar to the kill-a-watt power usage meter that's available in australia (and works on 240v). It occured to me tonight that it probably wouldn't be that great a leap from the arduino based mpguino to a watt-hour-guino-thingy. (wahuino?)

It's beyond me to design such a thing right now, though, but I thought I'd throw the idea out there. It would need to measure the voltage (between active and earth, and active and neutral to detect leakage) and current. And many, many times a second in order to get accurate figures. And I think calculating instantaneous watts, accumulated watt-hours, power factor, and also price if you can enter that into the machine.

I think the main thing I'd want is a computer interface - either usb or ethernet, which would up the price for sure but also could lighten the load on the arduino. The PC could do the crunching while the arduino just samples and sends. And you could log your figures.

Anyway, its asking alot I'm sure. But it's more of a wish than anything. I'm certain a basic version could be done for a reasonable price. And if they can do it with MPG in cars, why not kWh for homes?

[Ryland]

a bulky way to do this would be to get an old watt out meter like the power company uses, put a plug and an outlet on it, I've though about doing this for my water heater, otherwise you could put a few wraps of wire around one leg of your power cord, put it thru a rectifier and run a small dc clock, then calibrate it to work run as fast or slow as works well for your logging.

[NiHaoMike]

Use a transformer (must be good quality for good accuracy) and resistive divider for voltage sense and a Hall effect current sensor for current sensing. Put the two into the two channels of a sound card and use software to do it.

Or use something like a cheap FM transmitter and receiver (both must be stereo) so a simple resistive divider and a shunt can be used as the wireless link provides the isolation.