The idea is to build a very low cost energy monitoring system.
Sensors will be located at the point of use- typically either at an electrical
outlet or light socket. Both types will be small and pass-through and easily
user installable. Target price point for a sensor is single digit dollars.
Collector will collect data from all the sensors and relay to a PC or network
connection. Only one controller per site it needed. Price point for collector is
$10-$50 depending on functionality (cheapest being a simple USB gateway into an
existing PC).
Communication between sensors and controller is over the existing power lines
using a variant of the X-10 protocol.
Each sensor has a unique serial number and is transmit-only and is connected
directly to the AC lines. It uses the same connection for internal power, for
communications, and for monitoring.
Each sensor has three blocks- (1) power supply which provides operating power
for the sensor itself, (2) power measurement circuit which measures the power
being used by the connected load, and (3) communications circuit which lets the
sensor send its measurements out over the connected power line.
These three blocks would be implemented using a single low-end PIC
microcontroller and a handful of discrete components.
Notes on the implementation the power supply block here…
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011013
Notes on the implementation of the communications block here (only send stage
needed for this application)…
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en012050
Notes on the implementation of the AC power measurement block here (very simple
and cheap, but relatively unknown technique)…
http://electronicdesign.com/article/test-and-measurement/simple-digital-ac-wattmeter6411.aspx
All of these technologies are old enough to be unencumbered by patents now.
There is some design work to integrate these blocks into this application, but
it is straightforward. The sensors also need embedded software to make the
measurements and send the results, but again this is mostly cut-and-paste work.
The collector would need only an X-10 communications receiver. The simplest one
is just a gateway to an attached PC. A PC or a web application will present and
publish the collected data. You can buy off-the-shelf X10 gateways for less than
$20…
http://www.thehomeautomationstore.com/psc05.html
Higher-end collector models could have an embedded web server. Again, there are
off-the-shelf products that would work here.
I think that’s it. No really hard parts. Very easy to put together working
prototypes of everything. Innovation comes mostly in putting the blocks
together efficiently so you can hit the price point, and making the UI software
compelling. Some challenges could also come in getting regulatory approval (UL)
and scaling manufacturing, but they are well down the road.
I’d imagined that the initial products would look something like these…
(pardon my horrible freehand mouse drawing).
First is a plug adapter. You’d plug this into the wall and then plug a load
(desk lamp, computer, air conditioner) into it and it would watch the power
flowing through it. Second is a screw in adapter for light fixtures. Again, you
screw this into a light socket, then screw the light bulb into it and it watches
the power flowing though. Both contain the PIC (a tiny one) and all the other
necessary parts to measure the power and send the data over the power lines.
They are molded plastic, hopefully much nicer looking than my horrible freehand
mouse drawings.
11/2/2011: Published
11/08/2011: Added drawings