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Hello to all,
I am new to this forum. I found this website because I am trying to connect my OpenTherm boiler with an Arduino Duemilanove as explained at this website:
Now I want to place the Elektor PCB including the extra circuitry on a Carrier Card. I think this circuit is a nice idea for a plug.
Or if you really want to control your central heating system, a 2-way communication by means of an OpenTherm gateway is possible:
Just my 2 cents.
Greetings,
Templar
I was hoping to do exactly the same thing (already posted a while ago on the first link). I found both those links also, and not much more.
I'm hoping to use the schema from the first link, mostly because I already read the Elektuur article a while ago, and have the completed pcb here, already soldered.
Let me know how far you get, I'm not really an electronics wiz. :(
I'm interested in this, as my central heating also uses the OpenTherm protocol. However, I'm told that "Open" is not quite accurate - many manufacturers (all?) change the protocol in unspecified ways.
I would still like to have a go at this though. A (fairly large) plug would indeed be nice, two serial I/O inputs can be implemented in software using NewSoftSerial (if they don't communicate at the same time), so such a setup would tie up just one port.
As for control - I'm a bit hesitant to start controlling the house that way. All it takes is a runaway JeeNode/Arduino while there is no one around and things could get pretty nasty (though probably not dangerous if all you do is alter the temperature setpoint).
Do you have more info on the web, or pictures perhaps, of what you've done so far?
One more Q: what's the baudrate used by OpenTherm?
There is an link to a forumpage
I don't have more info on the web of what I've done so far. But I did the same as palebluedot.nl exept that I replaced resistors R1, R2 and R3 with 2 trimpots for fine-tuning the duty-cycle, I had problems with one of the input signals.
Bit rate is: 1000 bits/sec nominal
How about dropping all the opto-couplers and the rest, hooking it up directly to a JeeNode, sending out all the results by wireless, and powering this thing from the opentherm line itself?
One more interested!! I already have a computer controlled boiler, but I use on/off, with a FS20 switch. I did it to implement zone control, so that I can individually warm up different parts of the house. It is based on a mix of FS20 and FHT from ELV and it works quite well - startingt the fourth year of operation now! For a detailed explanation, see:
http://jaagpad.blogspot.com/2009/06/heating-system-rundown.html
But now I got a new boiler, and have been thinking and investigating OpenTherm, in the same links as already posted here. Currently I deal with runaway situations by sending a timed command to the FS20, or in other words, I tell the switch to turn on for about 70 seconds, and send the commands every 60 seconds, so if the computer hangs, the boiler will switch off. So maybe a hardware watchdog on a relay could make sure the arduino/jeenode is awake.
I found in the specification of the openTherm, that there is an openTherm lite or "-", which is controlled by the duty cycle of the switching. In the last days I have seriously been thinking of starting by implementing this, and then move one to the full fledged openTherm.
Of course I agree that the best option is indeed a standalone jeenode, powered by the openTherm :)
The boiler is sending current signals to the room unit. Too much current drop and the the current might get below 5...9 mA, the room unit is allowed a current consumption of 5 mA max. The interface might draw too much power. The heater I've got can deliver 24V power by screw terminals, I guess by installing the circuit near the boiler makes using those terminals an option?
Only, according to the OpenTherm specs the boiler interface shall provide safety insulation from the mains power line, that means no 24V power from the boiler?
We can probably get the JeeNode to consume well under 5 mA. The keyword is: average.
Regarding safety insulation: if there is no electrical contact to the JeeNode, then you can simply isolate the whole unit by placing it in a plastic box. That's why a wireless connection would be useful, IMO: you get isolation for free :)
I am also very interested in an OpenTherm-JeeNode interface. At this moment I have a JeeNode attached to my CV and responsible for several tasks:
- Listening to FHT room controllers (using an ELV RX868) , to find out of heat is requested somewhere in my home. When needed, the JeeNode closes a contact on the CV to indicate that heat is requested. The temperature of the CV is controlled by an outside temperature sensor (not via JeeNode).
- On and Off switching of a floor-heating pump (FS20 relay).
- By Opening/Closing a seperate contact, the CV can be put into power saving mode (no standby hot water).
Although everything is working now, I would really like to move to an OpenTherm solution with more functionality.
@pieterjm: Very nice setup! a bit similar to mine, but I use a FHZ1000PC to collect the data from the FHT's in a server, and then control the boiler with an on/off, not having a thermostat (in the Celsia sense) at all. I always thought it would be nice to run the whole thing from only an arduino! But with the server I have very nice logs of the temperature in each room. My interest in the OpenTherm is to indeed control the water temperature based on outside temperature and need for heat. Now I have it limited in the boiler, such as to hopefully get the best out of the condensing mode (so set to 55C), but as the days get colder I will need to adjust it accordingly... I could not yet clarify if the 55C limit for optimal performance is for the return temperature or for the warm water temperature...so I stay in the safe side...
One warning though, one year, all my the FHT's decided to stop sending the actuator messages...no idea why that happened...so since your setup is based solely on the actuator messages, you might need to keep an eye on that!
Jean-Claude,
> How about dropping all the opto-couplers and the rest, hooking it up directly to a > JeeNode, sending out all the results by wireless, and powering this thing from the > opentherm line itself?
Is that really possible? Is the 24V on the OpenTherm line not too high for a JeeNode? What would the scheme for such a setup look like?
Enfin, more questions.
Regards,
Pieter
It will need some extra circuitry, but no opto-couplers and no extra power supply. I've got it on my list to try this out (that's why I made the little portable logic-analyzer...).