Home Networking with 433Mhz RF

We seem to use quite a few low-cost wirelessly connected devices around the home. When thinking about how to realise my smart thermostat project I realised that it should connect to the boiler in the same manner as the current dumb thermostat, at least until some better technology with the right price point comes along.

Many of these devices use 433 Mhz and have undocumented proprietary protocols. Nevertheless, the price of these devices is right so I thought I would try to reverse engineer some of them, starting with the existing thermostat and an outside thermometer.

First step was to get some RF modules. I chose the Radiometrix ones as the supplier is nearby and user-friendly. Thx to Peter at the OHH meetup I knew to use a sound card and Audacity as a recording ’scope to see whet we’re dealing with. Next I wil convert the manchester-encoded stream and log a bunch of readings. From there I hope to be able to guess the protocol.

Along the way I found someone else doing this. See Bertrik’s site for details.

Once I’ve crossed that bridge I’ll hook up a transmitter and see if I can drive the boiler relay. Initially a simple arduino program will be sufficient to create a dumb theremostat. After that I’ll move on to optimisation taking into account internal and external temperature gradients.

If all goes well I can achieve another reduction in energy for heating without reducing comfort for the family.

Why don’t I just buy an optimising thermostat? I’ve tried to and failed so far to find anything at a reasonable price.

BRE Innovation Park

I’ve been trying for some time to get a pilot off the ground to see if others can obtain the same energy savings, particularly gas, that we have achieved using detailed monitoring. The Innovation Park at the Buildings Research Establishment was suggested to me and I was fortunate to meet Mike Perry who has been very much involved with this initiative.

The park is well work a visit anyway, especially if you plan to get involved in a new build or major rennovation project. However, I’m going to pick up on just two points here:

1. Monitoring is part of a much bigger picture that includes energy management, telecare, home entertainment etc. MP stressed the need for standards in this area. Widescale adoption of proprietary protocols around the home and community will make it very hard to get the full range of benefits economically. As with mainstream IT, good standards will permit the involvement of many innovators. Whilst it did happen in IT, it is unliikely that a single vendor’s proprietary will become sufficiently dominant to be considered “open”.

2. Gas, though important now, is not in most people’s thinking because it is expected to run out in the not-too-distant future. I wonder about this prediction given recent investment in pipelines from Norway and Russia. I don’t know the figures but I reckon there are millions of UK homes that will use gas until the price really does go through the roof. Solar hot water would have the effect of prolonging this.

OK, so I did not advance my grail quest but it certainly was interesting. I’m getting more and more interested in new build and this throws up a lot of ideas worth thinking about even if some of them, like complete airtightness, do not appeal at this time.

The quest continues: how can we get pulse outputs on existing gas meter installations? A second private meter in series seems to be the only solution.