December 1, 2008

A week or so ago I saw a post from James Governor on Twitter mentioning an “unconference” called Homecamp. Always keen to learn new things I investigated and found a link to the Current Cost meter, which provides a way to monitor one’s home electricity usage easily. Thinking of the days before large electricity bills this struck a chord, so I ordered one and spent the tail end of last week turning lights and electronic devices
off to see how low I could get the figure.

Homecamp08 took place on Saturday 29th November at Imperial College, and was organised by Chris Dalby, with help from Andy Stanford-Clark, Dale Lane, and James Governor.

The Current Cost Unit

Dale Lane started off by talking about the Current Cost meter, followed up by Andy Stanford Clark. Andy had already built his own DIY electricity monitoring solution, and then came across the Current Cost people. The Current Cost team were persuaded to add the serial port which has allowed people to do interesting things with the unit. It currently provides (every 6 seconds):

  • Temperature
  • Current Watts used
  • Hourly usage for the last 24 hours
  • Daily usage for the last 31 days

Code samples are available online in various languages to allow experimentation. The new unit, due out in December, will keep daily history for 90 days, and allow sensor readings on 9 input channels, as well as supporting a higher data rate.

Andy talked about other monitoring devices he has built, and how it is possible to build a monitoring system based on a low-power PC such as the NSLU2 running Linux or Viglen MPC with a small message broker (such as RSMB) that supports the MQTT protocol;
other devices can subscribe to published events and act on them (such as Twittering). Andy’s team have even equipped the Hursley bus to Twitter its location (how we could do with that on London buses).


So why should we bother about all this? Well, from a purely selfish perspective, one watt per year costs roughtly £1. So given that the meter costs around £30 (from Eco Gadget Shop) it doesn’t take long before it starts paying for itself. Having the meter constantly showing you how much you are paying (it is accurate to within around 10%) does encourage lower usage. And it shows you how much ambient energy your house is using when you are getting no benefit from it,
i.e. from devices left running, or on standby. We aren’t yet at a point where electricity is sufficiently scarce that this is an issue, but it could be in the future.

Dynamic Demand

Phoene Bright and Joe ShortPhoebe Bright talked about how dynamic pricing, based on demand throughout the day. There is typically a peak between 6pm and 7pm in the evening, which means that generators in the UK need to work at low capacity and then ramp up their output for the peak. Ideally we would like to spread demand throughout the day. Joe Short, who is involved with Dynamic Demand, joined Phoebe and described how it is possible to evaluate how well the UK generators are coping with current demand by measuring the frequency of the mains supply.


The IBM Hursley team have created their own network involving an element of friendly competition to compare and highlight energy usage. There was general consensus among the Homecamp attendees that social factors have a powerful impact on behaviour, more-so than economic factors. (Pachube – pronounced “patch-bay” – was covered on a later session and builds on this idea.)


The majority of the home automation and monitoring solutions being used are home-built. A very useful potential component for this is the Arduino module, which Nicholas O’Leary took us through. The unit has a number of digital and analogue inputs and can have other boards piggy-backed on top (for example, to introduce ethernet support). Nicholas has built an ambient orb based on the Arduino, which incorporates an illuminated sphere that provides constant feedback on the home’s
energy consumption (green / amber / red, for example).

Monitoring Gas, Water and Petrol Consumption

Other home-grown solutions involve monitoring gas based on light reflected from read-out digits, the pulsing LED, or boiler flame height. Andy Stanford-Clark was able to get another water meter installed which has a magnetised needle whose rotations can then be counted. And petrol consumption can be monitoring through the On-Board Display connector.

Honourable mentions go to Ben Hardill for his water monitoring unit that would be suitable for a flat, to Nicholas O’Leary for rigging up his doorbell, and to Adrian McEwan who is working on a fridge monitor.

In summary, there was lots to think about, much of it new to me. I felt a sense of excitement arising from the progress that people had already made, and that through a combination of social, economic and technological factors it is possible for us to continue encouraging individual and collective energy reduction.


Onzo designs in-home energy displays and smart meter solutions that enable utilities to put the end user in control.

Rob Veck is taking retirement early in order to work on Green Home Diary.

Write-ups from Dale Lane, Phoebe Bright and Tom Taylor.