Computing stuff tied to the physical world

OpenTherm data processing

In Software on Nov 19, 2012 at 00:01

Before going into processing the data from Schelte Bron’s OpenTherm Gateway, I’d like to point to OpenTherm Monitor, a multi-platform application he built and also makes freely available from his website.

It’s not provided for Mac OSX, but as it so happens, this software is written in Tcl and based on Tclkit, by yours truly. Since JeeMon is nothing but an extended version of Tclkit, I was able to extract the software and run it with my Mac version of JeeMon:

  sdx unwrap otmonitor.exe
  jeemon otmonitor.vfs/main.tcl
Heh – nothing beats “re-using” one’s own code in new and mysterious ways, eh?

Here’s the user interface which pops up, after setting up the serial port (it needed some hacking in the otmonitor.tcl script):

Screen Shot 2012 11 10 at 22 35 47

I left this app running for an hour (vertical lines are drawn every 5 minutes), while raising the room temperature in the beginning, and running the hot water tap a bit later on.

Note the high error count: looks like the loose wires are highly susceptible to noise and electrostatic fields. Even just moving my hand near the laptop (connected to the gateway via the USB cable) could cause the Gateway to reset (through its watchdog, no doubt).

Still, it looks like the whole setup works very nicely! There’s a lot of OpenTherm knowledge built into the otmonitor code, allowing it to extract and even control various parameters in both heater and thermostat. As the above window shows, all essential values are properly picked up, even though this heater is from a different vendor. That’s probably the point of OpenTherm: to allow a couple of vendors to make their products inter-operable.

But here’s the thing: neither the heater nor the thermostat are near any serial or USB ports over here, so for me it would be much more convenient to transmit this info wirelessly.

Using a JeeNode of course! (is there any other way?) – stay tuned…

PS. Control would be another matter, since then the issue of authentication will need to be addressed, but as I said: that’s not on the table here at the moment.

  1. I’ve been looking at OpenTherm.

    We do however have a Buderus heating installation which doesn’t use OpenTherm, so I’ll have to look for an alternative to hook it into my “home automation system”.

  2. Nice work!

    I’m still considering such a gateway next to the dedicated connection with my Remeha Calenta boiler. But I wonder: can you see the flow temperature and gas usage (heating and DHW) also using OpenTherm??

    I might need both interfaces to have max. info & be able to control the boiler from a smartphone…

  3. Hello, Yesterday I ordered the components for assemble the OpenTherm Gateway. And in the next day I’ll do the PCB by EagleCad.

    Great Job.


  4. Hello, I read the Post:

    concernig “OpenTherm interface”.

    does it act as Master and/or coexist with the legacy CronoThermostat?

    Could you make a more detailed Post describing your “OpenTherm interface” project?

    Best Regards

    Mirko Ugolini

    • Hello,

      The project described in those pages is the one on the blog.

      It acts like a master, and does not coexist with the thermostat. It completely replaces it, so it needs some higher power to decide what to do w.r.t. water temperature, as the jeenode is just a “dumb” repeater. It merely implements a rough OpenTherm hardware and communication layers, and the normal talk to a central node using the rf12 libraries from the jeenode, The jeenode could also be made to calculate the set point itself, based e.g. on external temperature or other data received from nodes spread around the house…that depends on your setup and wishes…

  5. My father has recently been tinkering with his central heating system (a retired engineer is still an engineer!), and incorporated a Salus rt500rf wireless thermostat. I haven’t had a chance to take it apart, or otherwise probe it, but I have noticed an “868Mhz” label on the bottom…

    That’s just asking for trouble isn’t it?

    • You mean, it remembers you of the days you were young and used your TV remote to go along the houses and change the channel ppl where watching ???

      You now wanna do that with your parents heating system ??

      Shame on you !!!

    • Days of old? You mean that’s gone out of fashion?

      Damn… I still like walking into electrical retailers with a “TV be gone” hidden in my hand.

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