It works! Opentherm Interface V2

We're Back after a very long break!

Last January I presented a schematic for a second version of Alex's JeeTherm to Opentherm interface.

Well Alex finally had the time to test it and it works.... almost :-)
The first part of the board related to the physical interface actually works (!) i.e. sending and receiving the bits and packets to the boiler. This part was done with good old technology and using an operational amplifier as an active load.

The second part of the board was designed to power the remote controller from the loop power supply. This one we knew it would be trickier.
Placing the small supercap (0.1F) as load of the regulator was a good idea as the regulator is output short circuit protected so charging current is maintained within reasonable levels. Our fear was that due to the big charge current for some time on power up, the boiler would give up communicating (part of Opentherm interface, in case a boiler is connected to a plain old thermostat).
The key problem was that the display, the backlight (even when disabled) and the Jeenode take too much current for the system to be reliably powered...
We will have to arrange a winter sunday meet to fully debug these problems...


Mirko Ugolini said...

Hi Silva,
I read your post.
Any news? how the proto proceed?

Could share the wall project and source?


Mirko Ugolini


Mirko Ugolini said...

Hi Silva,

I read your post.

Could you share the project?



J Silva said...

Hello all,
the project succeeded in reading and writing commands to the boiler. We were unable to power the interface and a jeenode from the loop.
The code is hosted by Alex (see my friends blogs).

R Oort said...

Has the reception of the Opentherm signals improved (or gotten worse), When comparing this V2 Design to the Version 1 schematics (using opto-couplers) ?

What parts are used ?
In the schematics of V2 i notice two LM358 Opmamp's
However on the Proto-PCB i only see one.
Also the LP2950-33 is lacking .....

J Silva said...

Hi R Oort,
The idea was to get a simpler interface and less power wastefull so that the controller could be powered by the boiler.
The LP2950-3.3 was not needed since there is one inside the JeeNode. The LM358 is a dual opamp, therefore two appear in the schematic (with different pin numbers) and only one physical IC in the proto.