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.

J3 Pinout

Pin Function
2 +3.3V
3 Ground
6 RX


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:

  1. Snoop the 433MHz signal with another receiver and log the data from the sensor directly
  2. 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.

mikepotts64 (not verified) Tue, 22/09/2009 - 10:50

Great find!

I have 2 of these on my Solar grid-tie, one measuring PV production, the other measuring house consumption. I would be grateful for any news on progress here.... 

My PV web site Here

Paul Metcalfe (not verified) Thu, 31/12/2009 - 22:47

In reply to by mikepotts64 (not verified)

Good morning,


Regarding the Efergy energy meters they are sold as two distinct models here in the UK.

The first only does an instantaneous display, the second also logs and has a USB port which interfaces to a dedicated software package which is free.

The logging version (Efergy elite)accepts up to 3 different current transformers (CT's) which are very cheap to buy and can monitor 3 different circuits or 3 different phases.


regards, Paul

Kevin Whitefoot (not verified) Wed, 06/01/2010 - 05:01

I also have one of these devices.  It is not necessary to hack the receiver.  Because the clamp is in fact a current transformer, you can simply put a resistor across a spare one and plug it into the microphone input on a sound card.  Sample at, say, one kilohertz for a second, calculate the root mean square and you have a value proportional to the current.  Linearity depends on the sound card, some have compression built in so you either need a calibration curve or, as in my case, decide that the only value of real interest is the fuse rating.  I use it to limit the household current by turning off space and water heating when the current exceeds the fuse rating.

Of course hacking the receiver makes sense if you want it wireless.  In my case the minimum six second measurement cycle would result in a lot of blown fuses, my computer reacts in less than one second.  In case anyone is interested the computer in question is an ancient 200Mhz dinosaur running Windows 98.  The program was written in VB6 (source code gone missing unfortunately, I keep promising myself to write a new version for GNU/Linux).

One final thing.  It doesn't measure VA either, it measures current.  It reads VA so long as the system voltage actually is the value you set.  In rural areas and areas where load various greatly according to season the system voltage can vary by several percent.  I have seen 240V in Norway in the summer, the nominal is 230V.

Rich (not verified) Mon, 06/12/2010 - 04:42


Seeing any signal loss? maybe due to weak signal..

The signal drop-out I'm seeing gives me '-----' on the LCD..

After seeing some photos, I see a problem. The receiver ant is vertical,
and the transmitter ant is horizontal. Cross Polarization is a signal killer.

Cross-Pol can cut your signal up a theoretical 20dB. Which is a massive loss. (-3dB=50% loss).

If the transmitter is installed sideways, it might help out a bit..