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Hello,

I am very interested in the OpenTherm Gateway, which brought me to this forum.

I have Remeha Quinta 28c and a Honeywell EvoHome system with R8810 OT Gateway.

With the EvoHome system I have nice temperature control in diffent zones, but I'm missing all the other options and diagnostics OpenTherm has to offer.
When the boiler has an error, EvoHome can't tell me, I cannot set other parameters trough my thermostat except for heating requests.
Heck, I can't even read out the current heating request status for the sum of all my zones, when I was expecting to get nice trendlines and historic data
Another thing I would like, is to add a second heating system (with on/off control), to control my natural gas powered fireplace in the living room, but EvoHome
Of course these shortcomings are a great fail in a expensive system as the EvoHome, which is not as sophisticated as it could be without much extra effort (only better software?).

I hope to solve much of these shortcomings trough the OpenTherm Gateway, to control and monitor my heating system better.

Previously, I had the Remeha Celia 20 thermostat, which gave me the ability to shut down the hot water preheat function at night.
I am not sure how the OpenTherm gateway can fullfil this function?
I was thinking about having the OpenTherm attached to a Raspberry Pi and shedule the Raspberry Pi to send the commands to the OTG on set times, but there might be easier ways?
Another alternative could be a good-old clock relay attached to a GPIO pin, but as far as I can see it's not possible to activate the hot water function over GPIO?

Hoping for your well appreciated input!

Kind regards,
Joep

It is possible to control the hot water function using a GPIO pin. That feature is not currently available in the firmware, but it would only take a few lines of code. So, download the sources and just add it.

But if you will have some kind of computer collecting information from the OTGW anyway, making that send the serial commands is even easier and more flexible.

The OTGW doesn't have a clock, so it can't do any time-based actions itself.

Okay, adjusting the firmware shouldn't be much of a problem, but you're right about letting a computer do the job when it is already there.
I think it would nicely combine with a raspberry pi.

Since I'm not very experienced with serial communication under Linux, will it be possible to have your program running in web server mode, and have a cron job writing to the same serial port?
Also, what would you suggest? Connecting the RaspPi TTL serial port to the OTG TTL serial levels straight away, or having Max232's each side, or order a USB version?

It's not a good idea to have multiple processes talk to the same serial port simultaneously on any OS. Transmitting may possibly work, but each received character will only go to one process, and not necessarily all to the same one.

If you only transmit data you may get lucky and it works most of the time. A better way is to send the commands to otmonitor using dbus or the relay port (default: 7686). That way they'll also be reported in the log, which may be helpful when trying to figure out why something happened.

When the wires between the RaspPi and the OTGW are short, you can get away with TTL levels (beware that OTGW uses 5V and RPi 3.3V, so you will have to do some level shifting). Otherwise get a USB version, or use a MAX232 on the OTGW size and a MAX3232 (3.3V version of a MAX232) or a USB->serial converter on the Pi side.

Okay, thanks for your information!

Do you have an example somewhere on how to use the relay port?
Is everything sent to this port sent out as serial command 1:1, or is there some header information or wrapping involved?

The relay port doesn't do anything magic. Whatever you send to it is forwarded to the gateway and the response is returned to the caller, if he is still connected. The simplest fire-and-forget way to send a command to the relay port is to use the bash redirection to TCP. This can also be done from a cronjob, eg:
0 8 * * * bash -c 'echo HW=1 > /dev/tcp/localhost/7686'
30 21 * * * bash -c 'echo HW=0 > /dev/tcp/localhost/7686'

Super, that's really easy!
Thank you, I will order a OTG quickly to start playing!