Creating an IoT thermostat (part I)

In the following few series of blog posts I’m about to explain how I made myself an internet connected (or IoT, if you will) thermostat.

What I own now (and will soon become obsolete)

Currently I’m controlling my house’s heating system with a Theben RAM 325:


My first goal was to get a some understanding of how the current thermostat was doing its job. I don’t own the manual anymore so I was more or less on my own to figure out how to use this thermostat. Well, it’s not overly complicated, and in the end I found at that the Theben RAM725 works as a replacement for the RAM325 so I could go use the 725’s manual as reference.

The left side if the thermostat houses a 12h clock. In the upper left corner we find an indicator which tells us tells us weather it’s in “normal” (day) or “energy saving” (night) mode. The picture above is taken with the energy mode in “normal”. On the bottom right side we can find the temperature setting which allows us to set the energy saving mode temperature. A more advanced version also has a second temperature settings used to set the temperature during normal operation. At the top right we find the program selection switch which has 3 pre-defined programs: automatic program (clock icon), forced energy saving program (moon icon), and the comfort program (the one that is currently selected) where the thermostatic taps decide the temperature.

What you don’t see in this picture is that behind the clock we can set “on” and “off” jumpers which are used in automatic mode. There is also a LED located at the front which indicates when the heating system is heating.


The back side tells us its 230V powered (connectors 4 and 5). Connectors 1, 2, and 3 are used to control the heater (gas burner, valve, …). Here are some wiring examples:

There is also a small adjustment screw on the upper left side which allows tweaking the temperature trigger point.

Although this thermostat does a good job in what it needs to do, it’s pretty cheap and reliable, but it’s not really the most sexy thing to have in house and for an embedded engineer that I am a perfect goal to tackle on my own!

The newcomer

The embedded device I’m about to use is the Raspberry Pi 2. The reason I’m choosing this device is simple: it has all the components that I need, it has support for many add-ons, it has a large community which may help you out whenever you get into trouble, it’s relatively cheap to buy and easy to find in stores, and I have already sitting one on my desk waiting for an application to be used in. Furthermore it has a pretty decent touch screen and all sorts housing available so that I don’t have to tech the entire system by myself.

With that given this will be the first article in series of 3 to 4 articles in which I’ll tell you how I came to build my own modern thermostat. Stay tuned for more!


2 thoughts on “Creating an IoT thermostat (part I)

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