[OpenTRV-interest] OpenTRV crystal frequency?

[Damon Hart-Davis]

Hi,

It’s providing the real-time-clock and by running at low frequency eats less juice.

The basic code running the RTC draws <2uA from batteries.

Rgds

Damon

On 11 Feb 2014, at 23:43, Derek Jennings <EMAIL ADDRESS HIDDEN> wrote:

> I was actually intending to use a clone with the 328 http://hobbycomponents.com/index.php/dvbd/dvbd-ardu/ardu-dvbd/arduino-compatible-3-3v-pro-mini.html so code space will not be a problem.
> 
> What is the rationale for the 32kHz crystal? Is it being used to provide timing for the radio transceiver?
> 
> Thanks Derek
> 
> 
> On 11 February 2014 20:54, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:
> Actually, the Pro Mini uses the 168:
> 
> http://arduino.cc/en/Main/ArduinoBoardProMini
> 
> which means not enough code space for the OpenTRV code as it stands, but it could probably be squeezed back in to 16kB with a little effort.
> 
> Rgds
> 
> Damon
> 
> 
> On 11 Feb 2014, at 20:52, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:
> 
> > Hi,
> >
> > The crystal requency on the REV1 AVR board is 32768Hz, ie about 32kHz rather than 32MHz.
> >
> > Internally the RC oscillator runs at 8MHz and is prescaled to 1MHz (or lower) for the CPU clock.
> >
> > Your board might do fine.  Check that there are no clashes of our pin uses on REV1 with other things going on on the Pro Mini.  You would need to fit 32768Hz crystal.
> >
> > Rgds
> >
> > Damon
> >
> > On 10 Feb 2014, at 16:02, Derek Jennings <EMAIL ADDRESS HIDDEN> wrote:
> >
> >> 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 https://github.com/delboy711/ArduinoOpenTherm.
> >>
> >> 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.
> >>
> >> Thanks
> >>
> >> Derek Jennings
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> >
> 
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