Current Cost and EDF EcoManager RF protocols almost fully decoded

Thanks to the enormous help of Graham Murphy, Matt Thorpe and Paul Cooper, the wiki pages for the EDF EcoManager RF protocol and the Current Cost RF protocol are nearing completion. Of course, jump in if you have anything to add. Anyone with a github account can contribute.

And my EDF EcoManager C++ AVR code is ticking along. Still some distance from being usable "in the field" but getting there.

One quick random thought: for those of us who have been tinkering with the Current Cost RF protocol, it appeared rather odd that the data is "manchesterised". It occurred to me this afternoon that we can take advantage of this structure in the data to validate the data. A little more discussion on the wiki.

UPDATE 30/10/2012

Current Cost have asked me to remove the protocol documentation from the wiki. More details here.

EDF EcoManager wiki

I've started a wiki page for technical details of the EDF EcoManager protocol. Please feel free to edit!

UPDATE 30/10/2012

Current Cost have asked me to remove the protocol documentation from the wiki. More details here.

Success pinging EDF IAM and receiving response.

EDF IAM with NanaodeEDF IAM with Nanaode

Yesterday my first EDF Individual Appliance Monitor arrived. These are very, very similar to Current Cost IAMs except for several vital differences:

  1. Each EDF IAM can both send and receive (the CC IAMs can only send).
  2. Each EDF IAM will only report its wattage when polled by the EDF EcoManager base station. This is great for my application because I should be able to completely avoid RF collisions.
  3. Each EDF IAM also has a relay to turn the appliance on or off. This relay can be activated using the manual override switch on the EDF IAM or over RF
  4. The packets appear to include a simple checksum! (The CC Transmitters don't bother with a checksum.)

I've made good progress today. I think I can now reliably talk to my EDF IAM and get replies.

Success receiving Current Cost RF data using RFM01 and RFM12b

At last! Some successes! Yesterday I finally managed to receive Current Cost RF packets using an RFM01 (the receiver module used on the Current Cost EnviR) and today I got my RFM12b transciever successfully receiving packets too! The RFM01 code is here and the RFM12b code is here. The code is still rather scruffy because I'm still very much in the prototyping stage. I've started attempting to send pings to my new EDF IAM but haven't succeeded yet. I'll blog with more details soon.

Blew up my laptop sniffing SPI bus of IAM!

I did something dumb. And expensive. And potentially dangerous. I blew up my laptop! How did I achieve this amazing feat? By connecting a Current Cost Individual Appliance Monitor to my laptop via a Bus Pirate (note the burnt patch of PCB on the top right of the photo!). I took care to make sure I was connecting the correct SDI lines, just as I had successfully done when sniffing data from my EnviR.

So why did I blow my laptop by connecting to an IAM?

Sniffing SPI data from my Current Cost EnviR

I've successfully sniffed SPI data from my Current Cost EnviR (firmware v 1.29) using a Bus Pirate.

Here's the back of the EnviR PCB. I soldered some wires onto the RFM01 module to make it a little easier to sniff data from the device:

The Bus Pirate is wonderfully easy to use. Just connect it up to the EnviR. Once the Bus Pirate is connected to a laptop, you can start talking to it using screen /dev/ttyUSB0 115200. Put the Bus Pirate into SPI mode and then start sniffing by typing (1). Easy peasy. Below are the results from some SPI bus sniffing...

Other wireless kit in our home

These are just some quick notes where I aim to list all the wireless kit in our home and the frequency on which they operate, so I can be confident that the 433MHz packets I'm seeing are from Current Cost kit.

Current Cost EnviR tear down

I may have to reverse engineer some parts of the Current Cost RF protocol. The first step may be to sniff the SPI bus between the EnviR's PIC and the RF module. Hence I've taken the EnviR apart. Here's what it looks like inside...


It's very easy to pull apart. You just need to tease the back of the plastic case away from the front using a thin but wide screw driver:

Current Cost Individual Appliance Monitor v3 tear down


What does a Current Cost Individual Appliance Monitor v3 look like inside? Let's find out... (click on a photo to view it full-size on Flickr)

Hacking the Current Cost

I have almost 30 Current Cost Individual Appliance Monitors (I need to monitor the power consumption of every appliance in my home for my PhD project).  Unfortunately, I sometimes see drop-outs on a single channel lasting thousands of seconds, which is simply unacceptable.  I see these epic drop-outs even if the IAM is within a meter of its EnviR.  So data is being lost somewhere between the IAM transmitting its packet and it being sent via XML from the EnviR.  I think the IAMs simply squirt a reading onto the RF carrier every 6 seconds without waiting for a "ping" from the EnviR.  There are two possible places where the packets are being lost:  1) the EnviR drops packets or 2) RF collisions

1) EnviR drops packets
If the EnviR is busy processing a packet of RF data when a new packet of RF data arrives then maybe it will fail to receive the new packet.  So if two IAMs send packets in quick succession then the second to send will be ignored.   The RFM01 only has a 16 bit buffer so it could easily overflow.  I have experiemented with setting two EnviRs to receive data from a single IAM.  Sometimes both EnviRs receive a packet; sometimes only one will receive a packet and sometimes both will drop the packet.  I take this as evidence that sometimes an EnviR will drop a packet because it's too busy.
2) RF collisions
An alternative explanation for the long drop outs is that some of the failed IAM transmissions are caused by RF collisions. How likely are RF collisions?  Apparently the Current Cost devices use a 4kbps data rate.  So a single bit take 1/4000 of a second to transmit so a single byte takes 8/4000 seconds = 2ms.  The RF packets on the CC transmitter are 16 bytes long. So a single packet takes 16 x 2ms = 32ms.  So about 30 packets can fit into a second and 180 can fit into the 6 second gap between IAM transmissions.  Let's make the maths simple and assume that we have 180 discrete time slots per 6 second cycle.  The chance of a single IAM transmitting in any given time slot is 1/180.  If we had only two IAMs then the chance of them sharing a single time slot (and hence colliding) is 1/180 x 1/180 = 1/32400.  But we have 30 IAMs hence we have a total of 30-choose-2 pairs = 435 pairs, so the chance of any pair colliding is 435/32400 = 1.3%; which is rather too high for comfort given that I want this logging to run for months and months.  And of course there are several reasons to believe the chance of a collision is even higher: we don't have discrete time slots and collisions can happen between any set of transmitters, not just pairs.  Ick.
My plan

First I'm going to assume that the main problem is that the EnviR drops packets because it's too busy.  Hence I want to connect an RF receiver directly to my laptop in order to sniff IAM data directly from the air without having to use an EnviR.  I'm somewhat out of my depth here!  After  a bit of googling, I came across this Nanode IRC conversation about sniffing the SPI bus of a Current Cost to reverse engineer their protocol.  I assume I just need a Bus Pirate to sniff the SPI bus of the EnviR to get the initialisation commands the EnviR sends to its on-board RFM01 RF module; and then I can buy an RFM01 module and connect this to the bus pirate's SPI bus to communicate directly with the RFM01 from my laptop.

If I find that RF collisions are a major problem then I may investigate the EDF wireless transmitter plugs.  These are similar to the Current Cost IAMs except, crucially, the EDF models use transceivers and not just transmitters.  The EDF Eco Manager base station "pings" each transmitter plug in sequence and the transmitter plug responds within about 20ms.  This should totally avoid RF collisions.  The problem is that I already have 30 Current Cost IAMs!  I'm planning to take one apart to see if there's any possibility of converting it to a trasceiver type (the IAMs say "transmitter only" on the back).  If not then I guess I'll have to try to return or eBay my IAMs and buy EDF transmitter plugs.  I'll still have to build my own transciever because each Eco Manager can only handle 14 transmitter plugs.  If I use multiple Eco Managers then RF collisions will become possible again.

Below are some notes on tools and forums...

SPI to USB converters

Logic Analysers

RF modules

Forum threads and blog posts

Current Cost specs


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