Low Temperatures & OpenTherm

I don’t know why, but the cold weather of the last few weeks makes the word “OpenTherm” go through my mind all the time… temperatures are in control of what keeps me busy, how about that 😉

While the Nemef Radaris Plugin is being tested, I have some spare time to try and make that first syllable in OpenTherm a bit more true. At least for me, cause I don’t know that much about the OpenTherm protocol yet – time to do something about it!

First I spent quite a lot of time searching for sources regarding OpenTherm and what I could do to make OpenTherm work for me. Sure, I’m building the OpenTherm Gateway that is described in detail here, but that’s not enough; I want to know more – everything there is to know! The biggest problem I’m facing is my lack of knowledge of electronics. So when it comes down to building stuff to interface with OpenTherm hardware, I have to fall back to schematics made by others. Sad but true.

So I started off with a document I already know about for a long long time (and that anyone who has ever searched the net for information about OpenTherm must have seen before): the Elektuur/Elektor article about the OpenTherm Monitor that was published in 2001. I’ve always wanted to build this Opentherm Monitor, but there’s a tiny problem with this OT Monitor: it needs to be connected to a serial port; not my favorite way of doing this. However, searching some more resulted in this site. Here you can find detailed information on how to connect a slightly modified OT Monitor and some extra components directly to an Arduino; that’s much better, for me.

Another good source of information is Alex Vieira’s blog, which is also mentioned on the JeeLabs Café. Alex’s approach is (as far as I can remember) different from others, cause Alex is using a JeeNode to act as a Thermostat instead of the ‘man in the middle’ approach that is being used by the Opentherm Gateway (injecting/modifying OT frames  between boiler and thermostat) that I’m building.

This made me wonder what would be the best thing to do; yes, I do want to control my central heating and yes, I do want to be able to change the temperature setpoint. But do I want to take over the role of the thermostat all the way and in fact make the current thermostat obsolete? No, cause in my opinion, our central heating system as a ‘basic facility’ that should always stay operational, no matter what. Computers can break down, the additional (DIY) hardware can suddenly stop working by some unforseen reason, or Murpy’s Law kicks in somewhere unexpected – all these things should never affect the service level of the central heating! OK, comfort level will decrease (cause if not, I’m doing something terribly wrong 😉 ), but we won’t have to be afraid of frozen water pipes, cause the ‘real’ thermostat will still keep the house warm enough. And just as important, problems can be fixed very easily by removing the additional hardware and things are back to how it was – as in a ‘normal house’.

You might think I don’t trust a DIY thermostat enough to replace the real one? No, that’s not the issue here – it’s more about creating something that can keep on working forever. Without me, my domotica system or any other piece of hardware I installed. Nothing I do should ever create an unusable house; neither should I be needed to fix things – that says it all.

Back to the original plan again, which is getting to know OpenTherm better.

The first step I made was ordering the OT Monitor @ Eurocircuits. Cost: 24 Euro for the PCB and with some components, the total cost is around 30 Euro.


OpenTherm Monitor Some components are still missing, but that won’t take long anymore. Next step will be to add the ‘extras’ I mentioned before so I can connect the OT Monitor to a JeeNode. These ‘extras’ have been ordered a few days ago and a JeeNode is already waiting to display some results on the 16×2 display. Total cost: not much.

Another great thing is that I managed to obtain a PCB out of a very small series that was produced for the OpenTherm Gateway I mentioned above; although I already started building this Gateway on perfboard, I’m happy to start all over again now I have this PCB 😉

OpenTherm Gateway PCB

To be continued!

Tagged , , , . Bookmark the permalink.

2 Responses to Low Temperatures & OpenTherm

  1. sjbasant says:

    what is your contact email adres?

Leave a Reply

Your email address will not be published. Required fields are marked *