Tasty tasty YAHMS

Apr 18, 2011 • john-mckerrell

I’ve mentioned a few times on recent blog posts about the Arduino project I’ve been working on to provide an internet controlled system for my central heating. I’m glad to be able to say I’ve finally got this working, but not only that, I’ve also opted to release the source code so that others can make use of it. The source code comes in two parts, the code to run on your Arduino and the code to run on the server side. I’m releasing both parts as Open Source Software as I realise that I’m not necessarily going to get time to add features that others need and by opening up the source code I can allow more people to get involved. I’ll be running the server side on yahms.net and will be letting anyone sign up to use the site. Right now that’s not hugely useful as new programs can only be added by inserting directly in the database but hopefully I or someone else will get around to knocking up some more UI and an API. I haven’t really mentioned what the site or the system actually does so I’ll give some brief summaries about the system and the hardware and then will be posting full build logs for all pieces of the hardware shortly.

A little more about the system in general then. I decided before Christmas that I wanted to be able to control my central heating from the Internet. What made me finally decide to do it was when I realised that my existing controller is simply plugged into a 3-pin socket meaning that all I needed to do was set the existing controller to be on constantly and then find a hardware solution that would allow me to get in between the 3-pin plug and socket to control the system. One of the things that made me decide I should build the system was the spate of cold weather we had. It seemed to come on all of a sudden so there was a number of mornings we’d wake up at 7am and find that because the weather was so cold the heating hadn’t been on for long enough. To solve this I decided I needed some intelligent temperature control that would turn the heating on earlier when we’re having a cold morning. A similar but different problem is when we go on holiday for a few days and come back to a cold house, with the heating controlled from the internet we’ll be able to have the heating fully off while we’re away but make it turn on a few hours before we get home.

So, the smallest part of the system is the temperature “probes”. Partly just to experiment with Xbee but also to get an idea for how the house retained heat I decided I wanted to put a few wireless temperature probes around the house. In theory they should be very simple just using an Xbee with a TMP36 temperature sensor feeding into them, in actual fact I’ve ended up with about 10 separate parts, most of which are there to make sure I get a steady regulated power source to the Xbee. Originally I had been hoping to power them from a battery-backed solar panel but in the end I’ve had to go with batteries.

To control my hall light I’m using a solid-state relay wired into the power line for the light. I had hoped to be able to make this non-invasive by wiring into the light switch but had difficulty getting the wire through the wall to the switch so ended up having to cut the line and re-connect it in a junction box which I could then wire up to my relay. The light is turned on by short-circuiting the two wires on this line and can be done either by turning my relay on or by using the existing switch. This means you don’t have to use the internet to turn the light on, but once the internet has turned it on you can’t turn it off locally, but that’s not a big deal.

To intercept the power to the heating I used an old mechanical timer with all the mechanics removed. This left me with a nice simple device which I only needed to short circuit two connections to turn on the circuit. A simple relay did the job here too and I had enough space left to add in a power module so that I can provide 5v USB power from it too, but more about that in the dedicated post. I can leave the existing heating controls set to “Constant” so that as soon as I turn the socket on, the heating comes on too.

Finally, to control the two relays and receive signals from the Xbee modules I put together a simple Arduino shield. It has an Xbee module connected to receive the signals, some wired jacks to send signals to the relays and also a temperature sensor, just “because”. The Arduino also has an Ethernet shield so the software is able to download configuration from yahms.net and turn the relays on and off in response to that config, it can also submit sensor readings back over the connection too.

So that’s the general overview, I’ll go into more detail in the next few posts and talk more about the software as well as the hardware and what they’re both capable of.

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Apr 19, 2011 — Frankie Roberto

Congratulations, you've finished the project just as it's gotten warm enough to turn the central heating off for the summer... :-) Seriously, sounds like a really interesting project - I'd really love to be able to replace the stupidly simple central heating timer in my house with an algorithm. I've only got as far as thinking about a feedback loop for measuring the effectiveness of an algorithm though. Basically, you'd want there to be buttons somewhere for 'I'm too cold' and 'I'm too hot' - and then to record the time, date, temperature(s) and system status every time one of those buttons were pressed. The aim of the algorithm would then be to reduce the number of times in which the buttons had to be pressed, whilst using as little energy as possible (as otherwise the heating would just stay on all the time). The algorithm could learn from previous button presses, as well as factoring in things like weather forecasts and possibly your holiday schedule. Frankie

Apr 19, 2011 — john

Thanks, ideally it'll mean that as our weather jumps between HEATWAVE! and SNOWPOCALYPSE! my system will be able to able to respond accordingly. Ultimately I was intending to have the controls work by having you specify a desired temperature in specific rooms at set times of day and the heating would work out what it needed to do to achieve that, I quite like your suggestion for being able to say "I'm too cold" though of course you'd probably also need some way to add timings in or some way of saying I'm leaving now but I'll be back in X hours. Being able to turn the hall light on has already been useful a few times too when we've arrived home late, though obviously that one will become less useful too as the days get longer.

Apr 21, 2011 — Ken Boak

John, I'm working along similar lines. I've had an Arduino controlling the central heating and hot water since last October - almost without a glitch. It was also logging the gas usage, and the temperature of 2 rooms and the hot water top and bottom on a minute by minute basis. My working day begins at 5:25am, so I monitor the outside temperature throughout the night and make a decision at 4am on whether to bring the heating on early or not. I can program exceptions into the timer - for examples Thursdays and Fridays when my wife is at home and needs heating during the day, and also Sats and Suns, where my day does not have to begin at 5:25am! I have a 110 year old house with solid 9" brick walls - which needs a bit of heating. I use the strategy of getting it up to temperature, and keeping it there within certain comfort bands. Letting it get cold and having to bring it up to temperature again is very wasteful of gas. The opposite could be said for a modern, well insulated house - with almost no thermal mass. The point being that every house has its own thermal requirements - and they are all different. What is needed is an intelligent controller whiich learns the thermal response of the house and to some extent the patterns of heat usage of the occupants. I hope to make some more progress on this over the summer, in time for next heating season. In the meantime I have produced a small Arduino like ethernet node - which will be used for remote setup and monitoring of the heating system. The "Nanode" is open source and we are about to build a batch of 100. All of the Nanode details and my home heating endeavours are on my blog - in the posts over the last 2 years or so. http://sustburbia.blogspot.com/

Apr 21, 2011 — Ken Boak

Frankie, I agree that most heating controllers are unbelievably crude. They rely on feedback from normally just the one thermostat, which is often located in the most inapropriate place in the house. In my house the thermostat used to be in the hall, which for some reason had an oversized radiator, and was the draughtiest space in the house. I quicky moved to a wireless thermostat which I located in the living room - the room which is occupied the most. I then found I could hi-jack the wireless boiler-on/boiler-off messages produced by the wireless thermostat and use an Arduino device to control the heating based on a series of room temperature, outside temperature and hot water tank sensors. As well as poorly located thermostats, older heating controls were often wired into the airing cupboard - out of site. No body wants to go upstairs to the airing cupboard with a torch and grope around trying to change the time settings on their heating controller. The best approach would be to have a modern, stylish wireless controller, which can be placed on the coffee table or sideboard, or carried with you from room to room, as you change patterns of occupancy. Using wireless controllers, each of the house occupants could set their room-space to their preferred temperatures. Some years ago I fitted thermostatic radiator valves (TRVs) to most of my rads. Using a small 1 or 2W power resistor or transistor as a heating device attached to the TRV bulb, you can individually control the radiator from fully on to fully off in about 15 minutes. Whilst this does consume some extra electricity to keep a radiator off - that is nothing compared to the energy wasted in gas keeping it on unnecessarily. I'm developing a plug in, wireless room controller which can control a TRV, measure room temperatures (at floor and ceiling) and determine activity/occupancy. This would be used in association with the hand-held thermostat/heating/energy display. In the last 5 years, there has been a lot of developments in energy monitoring for electricity - however we should really be looking at the much larger energy usage in the household which is gas or oil for heating.

Apr 22, 2011 — Ken Boak

John, Frankie, I have also been working on ideas to allow room occupants to get visual feedback of whether a room is above or below their prefered comfort temperature. Rather than a numerical display, I was thinking of something more like an "Ambient Orb" which is essentially an RGB LED in some sort of spherical diffuser. When the room is below the comfort zone temperature, the lamp would glow with a blue colour, slowly fading up to a greenish hue when the comfort temperature is reached. Above this temperature, the globe fades through orange and eventually red to show that the room is well over temperature, and that gas consumption may be excessive. The whole colour fading response would probably only cover a temperature range of 17 to 21C. My wife is always complaining that the living room is cold, when such an orb would show that it's actually at the comfort temperature. Perception of comfortable temperature can be a very individual thing.

May 18, 2011 — Paul Tanner

Ken, You may never be able to keep your wife at a happy temperature because it depends on her movements. Maybe you should also install a Kinect sensor and get your system to incorporate movement into the calculation ;-)