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Thread: OpenTherm VR33 and Vaillant ecoTEC plus 428

  1. #41
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    Is your board cheaper than $15?
    https://ihormelnyk.com/opentherm_adapter

  2. #42
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    By the time I allow for postage etc then it works out very similar. That is a good suggestion though as that board is pretty small and so I could stick it underneath and bypass the OT part of my existing board. It will save me a bit of effort in redesign/build.

  3. #43
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    I used this for a while and that too was quite nice. Except that since these boilers are not natively OT, I figured there was nothing to gain beyond my eBus interface. So I sold it on here.

    https://www.ebay.co.uk/itm/Orange-Pi...-127632-2357-0

  4. #44
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    Quote Originally Posted by bruce_miranda View Post
    Is your board cheaper than $15?
    https://ihormelnyk.com/opentherm_adapter
    Unfortunately it turns out he is in Ukraine and unable to supply these at present for obvious reasons. He was kind enough to refund my payment right away though.
    I then tried ordering a similar board from https://diyless.com/ but that seems to be stuck somewhere in Ukraine too.

    So I'm now back to getting some new versions of my own board with the correct optocouplers this time. Hopefully they will be here in a couple of weeks and I might be ready to test again.

  5. #45
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    I've built up my own revised board now with the 'correct' optocouplers and it now works perfectly!! I can set the boiler temperature and read back some data e.g. feed and return temperature.
    Just need to finish writing the Arduino code to accept the temperature commands from my server now.

  6. #46
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    Care to share your circuit and code?

  7. #47
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    I'm just using the circuit shown here https://ihormelnyk.com/Content/Pages...chematic_o.png and also the same here https://registry.platformio.org/libr...raus/Opentherm
    The code is using the J Praus opentherm library and I've based my code on his example. The only real change was to add a timeout into his 'conversation' handler so that it would reliably detect if the boiler didn't respond.

  8. #48
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    I'm guessing this interface can only monitor the OT traffic, it cannot actually inject or alter a command? That would require a gateway?

  9. #49
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    No I'm using it to generate OT messages into the boiler (VR33 interface) e.g. set feed temperature and also to query data e.g. feed and return temperature. So it's acting instead of a thermostat.

  10. #50
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    I've been trying this out but I'm having some problems.
    Whilst the loop is applied to the VR33 OT connections then the boiler works fine in response to the 240V demand signal as it always did.
    When I connect the OT up to my Arduino and start sending commands I can see the boiler is receiving the feed temperature control correctly but it never fires up. It seems to be ignoring the demand signal.
    I had initially not been sending the OT slave config message so I thought perhaps that was an issue so included that with the ch_enable bit set to 1. Still no change though.
    As soon as I put the loop back on then it fires up correctly.
    Any thoughts what might be wrong?

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