Being rather jealous of the energy monitoring capability that my parents now have I went online to order my own Open Energy Monitoring (OEM) system. I was hoping to have a play as a Christmas project. Firstly when I did I was pleasantly surprised to discover that the price had come down and that they now had an even cleaner more logical way to determine what you need in the form of pre-built bundles emonTx V3 - Fully Assembled option in their store. Now these had been present previously but as a tick list and after completing the tick list the price was always significantly more than £60 result you get from the assembled bundle. I also needed a RFM12PiV2 (£22) to talk to the emonTx unit, AC-AC power supply (£10) and a CT cable (£10) [prices have been rounded as in the LightwaveRF case above]. So with shipping the total price came to around £108. Annoyingly I did not find the discount code -> GPDGZ0P66 <- until much later during the installation process otherwise I could have saved another 5%. I feel it should be something that is automatically triggered when you purchase the assembled bundle but such is life - supporting the cause and all.

I had resigned myself, due to the late ordering date, that I would not see the unit until after Christmas. With that in mind I was pleasantly surprised when the man from Royal Mail turned up with my parcel on Tuesday 24/12/2013 so I had the entire of Christmas to play.


Unpacking the unit all I needed to do was find a plug socket near my consumer box. Attach the CT cable to either the live or neutral lines and connect both cables to the emonTx unit. I was able to tweet @Openenergymon for advice as I was going along as well - which was pretty damn cool (note tweets to @LightwaveRF have still not been answered). So job done! Next I need to connect the RFM12PiV2 to my Raspberry Pi. This was a little more tricky as I had to struggle with my clear plastic Pi case and then decide which of the Pi logo holes to feed the RFM’s aerial through. With that done it then came down to setting up the software. Something I was honestly dreading after failing to get EmonCMS to work with my Pi previously. The hardest part was finding the correct guide on the EmonCMS website if I am honest. This appears to have been significantly updated in recent weeks but if you are interested I used the instructions:

Again this was confused by me making a typo and reading “add extension” to mean write “add extension” and not “extension” into a file - BERK. Plus a major mistake in that my Pi connector module was newer than my EmonCMS base. This happened because of they way all the modules are stored in separate GIT projects which means there is no simple way to get them all. Instead you must pull each GIT repo down. Which I did do but forgot to update the EmonCMS git itself. Modules I added included:

  • PacketGen, A new module for sending control packets.

  • Event module for sending Prowl, NMA, Curl, Twitter and Email notifications.

  • MQTT module for subscribing to MQTT topics containing data to be logged to emoncms.

  • Notify module sends an email if feeds become inactive

  • Energy module. Create a David MacKay style energy stack

  • OpenBEM module. Open Source Building Energy Model. Investigate the thermal performance of buildings.

  • Report module. Create’s electricity use reports including appliance list exercise.

To be honest I’m only really aware of this list as it comes directly from the emoncms instruction webpage - Raspberry Pi + Harddrive + Emoncms. Again this has changed significantly since before Christmas.

As soon as I had fixed the issue I found that my EmonCMS could see my emonTX and then I started to follow the guides for making the EmonCMS show something useful:

Screenshot_2014-01-12-09-04-49But I actually found the OEM setup page most useful source for links and instructions. Even now I’m not certain if I have missed a step with my feed setup and should have an input combing the AC and current measurements?

However once the feeds were in place and once I had followed the dashboard guide I could very nicely visualise my data using my phone. Of course all the Pi related setup actually took me about a day to undertake. This includes moving the database locations from my SD card and onto my portable drive.


emonsWell once setup the operation has mainly been me looking at the EmonCMS website on my Pi using all range of devices and looking at both real power usage in Watts or various other plots in kWh, kWhd, etc.

Actually making nice looking dashboards are very easy indeed - although you do reach a point where they get a bit samey. The one on the right here is my “live” usage. I have my total kWh my min/max, live power in W < 0.5 kW in the centre and kW as an inset. Not forgetting the live usage in W in a graph below. At the time of taking the image I was in the middle of doing a load of washing and of course this blog.

I’ve also written my own MySQL script to digest my daily usage and provide me with costs per day based on my two tariff power supply. I’m also building a nice historical record of power usage. Have min/max logs per day and generally finding the whole thing rather cool. I have of course done the search of the house and worked out how much juice each device draws when turned on. And yes I am currently looking to make a new daily minimum draw, currently standing at 24 W (40 W on the day of the image above and 32 W when I was using my phone to look at the usage, picture further up).


Sadly nothing to report here but watch this space as within EmonCMS there is an Extras menu and within that an “RFM12b Packet Generator” menu link. I think it will be a case of discussing with the forum and looking for an appropriate set of generic WiFi enabled plugs - perhaps even LightwaveRF ones?


Bloody marvellous! No seriously my worries about setup of this system being “opensource” and “openhardware” as if these two things intrinsically mean more work was completely wrong. Yes the Pi stage was a mess but that was partially my fault. Then end product is much nicer than the LightwaveRF for me anyhow and the responsiveness of the OEM to tweets is just amazing.