Once the thermostat choosen, the next move was to see how to interconnect the Raspberry Pi and the Z-Wave network.

USB Sticks

After investigation, it appears that there are 2 possibilities by 3 main manufacturers:

The other possibility, still by Z-Wave>me is called the Razberry and is an add-on for the Raspberry Pi. Cool... but not really future-proof.

The solutions by Z-Wave>me seem to use a specific software called Z-Way and running in Javascript. Unfortunately, the documentation is very scarce and in the end I went for the Stick compatible with Z-Wave plus.

Sigma Designs UZB


As I mentionned before, Z-Wave is a very closed world, at the opposite end of Open Source. Fortunately, reverse engineering was done and there is a Z-Wave free software library called Openzwave. There is even a Python wrapper!

First tries

If the compilation part takes ages, it is totally painless. But all first attempts were failures and I couldn't understand what was going on... Even using the control panel. Associating 2 of the elements (Thermostat, actuator, static controller) was fine but all three together didn't work as I expected. Even following the numerous recipes found on the forums.

Then I found a way which works for me:

After this, the all 3 elements are connected:

Now, what can I do?

Z-Wave learning curve is rather steep and badly documented (because of the NDA).

Another particularity is that almost everything is asynchronous... and very slow. Especially when it comes to the SSC317. In order to minimise the battery usage, operation can wait for... hours!

Other example, on the Control Panel, things can take several minutes before one received a response. Not talking about the state of the network which most of the time doesn't seem to reach the "Ready" level! :-(


Well, the thermostat is recognised by openzwave but half the interesting functions are not (yet) implemented. It looks like if openzwave was mainly developed for switches and relays. Sadly enough, anything around the schedule commands (0x53) are not taken into account so there is, at the moment, no way to read/write the 7-day programme.

I wasn't able to read either the current temperature set point (which is odd because it should work).

After playing a bit, I decided that Z-Wave is not yet totally fonctional without a proper certified box. I'm still wondering what the implementation of Z-Way is like and if it is more advanced than openzwave.


The values I can access to are:

For the moment, I shelved idea of overriding the On/Off of the heating remotely (but this works fine). Since I want to use Python3 for the main software and this project is in Python (or C++), the simplest set-up was to have both running separately.

One process is responsible for the z-wave management. Every 5 minutes, a refresh of value is requested (will be honoured... or not) and a few second later, a JSON value file will be dumped.

The main process can then read this JSON file and do what it wants with the values (mainly sending them to RRD).

I'll re-evaluate my options at a later stage.


    In need of a good thermostat for my boiler, I investigated about the models and technologies available.

    The requirements were :

    • Reliable & Safe (I don't think it's a 230V commutation (more around 24V) but still...)
    • Voltage-free contacts
    • Programmable over 7-day
    • At least 4 settings per day (on/off morning + on/off evening)
    • Programming times with 1/2 hour steps max
    • Wireless if possible
    • Autonomous (no obligation for the Raspberry Pi or any other micirocontroller to be on)
    • Connectable to a home automation system if possible
    • Remotely programmable if possible
    • Remote override of settings if possible

    Trouble is, the perfect thermostat doesn't seem to be available in France. During my investigations, I found the following options :

    • Wired option: Cheap but not wireless and not connectable to an external system
    • Proprietary wireless: Usually not connectable either
    • Wifi thermostats - local server: The best (on the paper) seems the one from Heatmiser but they can be quite expensive, need permanent 230V and are wall mounted. Moreover they don't seem to be distributed in France. But the API is documented.
    • Wifi thermostats - cloud: The latest trend: Nest, Tado°, Netatmo, etc... I DON'T want to rely on a internet connexion to command the heating nor I want to upload private data (being in or out) to a private company. Privacy and risk of ending up with a useless piece of hardware if the manufacturer disappears render this solution a no go.
    • Chacon/DI.O/MyFOX: Didn't find anything available
    • EnOcean: Didn't find anything available/suitable
    • Z-Wave: Horstmann/Secure seem to fulfill the requirement

    Secure SCS317

    Horstmann (the old brand name) seem to appear on all the home automation forum, especially the model HRT4-ZW. Secure (the new name) released recently a model SCS317 (sold as kit paired with the actuator SSR303 under the name SCS318) which is ticking almost all the boxes of my list.


    It is a 7 day programmable thermostat with 6 temperatures settings per day, temporary override, holiday mode, TPI (Time Proportional & Integral) and speaks z-Wave.

    It also has a ten-minute resolution, so I could programme some heating from 06:40 to 8:20! My old thermostat could only do hours (for example from 07:00 to 8:00).


    The main feature is the fact that it is a Z-Wave product so (in theory) compatible with loads of other products and Home Automation boxes. That said, Z-Wave is also very much a proprietary wireless technology (even the access to the API is under NDA!!!!) and seems quite complicated to control from homemade solution. But this will be for next time...

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