Comment by lhl | Hacker News Reader

Comment by lhl | Hacker News Reader

There's another pretty similar Kickstarter project going on right now. It's wifi (802.11n) vs BLE - looks pretty sharp. It lacks beaconing but has a similar open API and also looks pretty well designed: http://www.kickstarter.com/projects/plugaway/plugaway-your-s...

Both have online load/consumption monitoring (I wonder how exactly the Zuli stores/handles that when there's no app around?), which are probably the biggest thing separating them from existing remote power outlet products.

(For logging power, the only relatively cheap options I've found is hacking a Kill-A-Watt sensor chip (see: http://www.mikesmicromania.com/2013/04/moteino-kill-watt-har... ) or buying a Watts up? PRO - both are more much more expensive/involved solutions than either of these two new devices.)

I believe that one way to measure the current for relatively cheap would be to break the neutral line and throw a current-sensing resistor in it. It would create a small voltage drop across the resistor. If you know the voltage drop and the resistor value, it should be pretty trivial to determine the current through the neutral line. Equation to do that would be:

lineCurrent = (Voltage of the current-sense resistor) / (resistance of the current-sense resistor)

Considering a current sense resistor is fairly cheap (http://octopart.com/13fr200e-ohmite-988758) it shouldn't be terribly expensive to do. You should be able to throw that between a Vin- and Vin+ on a linear optoisolator and send the values back to a microcontroller to be reported.

I'm not an EE though, so grain of salt.

Yeah, in theory you could build your own but having something UL rated is an advantage. AC is a lot more dangerous than DC, so you should really know what you're doing before mucking around.

There are a few more components for building a basic board: https://instruct1.cit.cornell.edu/courses/ee476/FinalProject... http://enerjar.net/Hardware.html

Building a more accurate power meter is pretty involved: http://coolarduino.wordpress.com/2013/02/08/power-meter/ http://coolarduino.wordpress.com/2013/02/27/power-energy-met...

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