I just bought an Efergy wireless power meter on Ebay. It consists of a hall effect current meter clamp that clips around the mains line to your house, an RF transmitter module, and a receiver module with an LCD display that shows various bits of information that it gathers. The same meter was also sold at Aldi recently under the brand "Trade Power".
The goal of the unit is to show your instantaneous (well, to 6 second resolution) power consumption for your home. Its not quite accurate, as it is actually measuring VA rather than Watts, as such, it will always read higher than your actual power consumption, since the best case is that VA = Watts when the power factor is 1.
One thing the device is missing is the ability to connect to a PC to allow for logging of data. Of course, the first thing I did when I got the machine was to open it up.
The circuit is quite straightforward, a 433MHz RF receiver module, an NEC D78F0511 microcontroller (44 pin), a PCF 8562 LCD driver, and a small IC that I can't identify (labelled L16 6Q02W). There is empty space on the circuit board for an alternate RF reciever, as well as what appears to be a serial to USB IC and mini USB connector.
Interesting, perhaps this has the ability to output data on the serial port? Checking the datasheet for the microcontroller, there are 2 serial ports available. One is connected to the RF module, the other appears on header J3.
Connecting the port up to the computer at 115200 (8,n,1, no flow control) produces the following output (in hex) repeated every 6 seconds:
2e 9e d1 20 ff 20 1 2e 9e d1
These values do not change with varying power usage, so I'm not convinced at this point that the data is available.
I have a couple of other options:
- Snoop the 433MHz signal with another receiver and log the data from the sensor directly
- Monitor the (segmented) LCD lines and "read" the contents of the LCD
Update 13 October 2009
No real progress made here (I'm busy with other things), but someone else has the same idea to snoop the 433MHz signal. Unfortunately, at the time of writing, they haven't made any progress either.