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

udev rules for Current Costs

Update Oct 11th 2012

It may not be necessary to add a new udev rule to access a CurrentCost (or program a Nanode). Instead it may just be necessary to add yourself to the dialout group. Haven't tested this on a new installation yet.

udev manages the /dev/ filesystem on a modern Linux machine. When you first connect a Current Cost USB cable to a Linux machine, you may find that the relevant /dev/ttyUSB[0-9] file has not got the correct permissions to allow you to access it as a normal user.

These are the steps that allowed me to connect my Current Cost to my Ubuntu Server 12.04 machine:

  1. I added my username, jack, to the fuse group with the command sudo usermod -a -G fuse jack. (The -a (append) is ESSENTIAL! If you forget the -a then your username will only be in the fuse group. If you accidentally forget the -a then boot into Ubuntu recovery mode, then run a disk check (to mount the filesystem as read/write), then drop into root command line mode, then issue the comman usermod -a -G sudo username as per the instructions here and then you can add yourself to the default groups listed here.)
  2. Log out and log back in again for the group changes to take effect (it isn't sufficient to close the terminal and open it again).
  3. I created a new file /etc/udev/rules.d/current-cost.rules. This file contains the following text:
    SUBSYSTEM!="usb_device", ACTION!="add", GOTO="currentcost_rules_end"
    # Current Cost (the following rule should be all on one line)
    ATTRS{idVendor}=="067b", ATTRS{idProduct}=="2303", MODE="660", GROUP:="fuse" 
  4. After saving this file, I unplugged all Current Cost EnviR monitors from my machine and plugged them in again. (Note that running sudo service udev restart doesn't appear to be sufficient or necessary to start using the new udev rules.)
  5. Check that the permissions have been set correctly by running ls -ld /dev/ttyUSB?. The result should be something like this: crw-rw---- 1 root fuse 188, 0 Aug 10 08:43 /dev/ttyUSB0 (the crucial things to check are that group has read and write permissions and that the group is set to fuse)

A quick explanation of the udev rules

Each line is a rule. udev checks the truth of all == and !=; if those checks all succeed then it evaluates the assignment operators = and := (the second of which ensures that the value assigned to that key isn't changed by a subsequent rule). Let's consider the line which starts ATTRS.... This will set MODE="660" (owner and group have read and write permissions) and will set GROUP:="fuse" (:= ensures that the group will not be changed later) for all devices where ATTRS{idVendor}=="067b" and ATTRS{idProduct}=="2303".

How do we which attributes to check for? If we only care about idVendor and idProduct then plug the device in and run lsusb

jack@lenovo:~/workingcopies/iam_logger$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 004: ID 5986:0241 Acer, Inc BisonCam, NB Pro
Bus 001 Device 006: ID 0bda:0158 Realtek Semiconductor Corp. USB 2.0 multicard reader
Bus 002 Device 026: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port
Bus 003 Device 002: ID 0a5c:2150 Broadcom Corp. BCM2046 Bluetooth Device

The line Bus 002 Device 026: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port is my Current Cost USB cable. If we want finer control then run udevadm info --name=/dev/ttyUSB0 --attribute-walk to see a long list of key, value pairs you could use in your udev rules.

More info:

Windows Notes

Just some random notes about using Windows

Backup batch script

Below is the batch script I use to achieve the following behaviour:

  • Copy files from hard disk to a USB disk.
  • The backup procress must never delete a file from either source or destination, except for the Photos director.
  • The end result is that the destination ends up having more files than the source because files are never deleted by the backup process. But the Photos directory on both disks should be exact copies.
REM tutorial:
REM options:
REM /e    = copy all sub-folders, even empty ones
REM /mir  = mirror (check the files in the destination, and only copy newer files)
REM /np   = no progress counter
REM /log: = create a logfile
REM /xo   = exclude older files
REM /xd   = exclude directory
robocopy D:\ I:\Backup\Storage /e /np /log:backup_log.txt /xo /xd $RECYCLE.BIN RECYCLER "System 
Volume Information" Photos
robocopy D:\Photos I:\Backup\Storage\Photos /e /mir /np /log:backup_photos_log.txt

Setting up Emacs for Python development

  • Ubuntu packages to install: emacs autocutsel texinfo git mercurial (git and texinfo are required by el-get; mercurial is required to install pymacs)
  • To set the font size for just this session: press M-: and then type (set-face-attribute 'default nil :height 100) (taken from stack overflow)


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