[OpenTRV-interest] OpenTRV crystal frequency?

Mon Feb 10 16:02:44 GMT 2014

Hi New subscriber to the OpenTRV list here.
Maybe this question has already been answered. but I have not yet found the
list archive.

I notice from the OpenTRV schematic that you are using a 32MHz crystal for
the ATMega328.  What are the implications of using a different frequency?

I discovered OpenTRV after building an Arduino based Opentherm gateway
between my spanking new Intergas boiler, and its (not so) intelligent
Opentherm controller from Remaha.  You can see my project details at

One of the reasons I built it was because when my living room is up to
temperature I wanted to tell the boiler to keep supplying heat for the
radiators in other rooms. This naturally requires me to control the rads
with motorised valves and to communicate with the valves which led to
discovering OpenTRV.  (That's what I love about OpenSource. No matter what
you want to do, someone, somewhere is already working on it!).

I have a motorised valve on order from Conrad (the 561800-89 ), and had
planned to use a 3.3V Arduino Pro Mini and an RFM22B radio unit to listen
in on the protocol.  But the Pro Mini has an 8MHz resonator hence my
question why OpenTRV uses 32MHz.


Derek Jennings
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