Re: Software for Central Heating Control

[meow2222@xxxxxxxxx]

Steve S wrote:
> "John Rumm" <see.my.signature@xxxxxxxxxxxx> wrote :
>
>
> <mega snip>>
> > Have a look at some of the many X10 and home automation sites.
> >
> >> What is the best hardware?
> >
> > Define best?
> >
>
> You need to be very careful with projects like this, especially when you
> have loads of sensors and functions. They introduce very many corner cases
> and single points of failure. You will need to do a lot of very methodical
> testing. What happens when a sensor fails? Can you detect it and act
> appropriately? In the system I am designing (using C, by the way) it is
> designed to fail passive, reverting to the old control system.
>
> Most SBC solutions use cooperative multitasking. This requires careful
> coding in order not to break it.
>
> Also, plan what to do if you decide to move house. A homebrew heating
> control system is not likely to add to the value of the house. In my case I
> shall be able to revert to a normal if somewhat outdated control system at
> the drop of a hat.
>
> Dallas 1-wire sensors are OK, but bear in mind that for any significant
> distance you'll need twisted pair cabling. Also think carefully about the
> interface to them. If interfacing directly to an SBC the timing is critical,
> and you'll need interrupts turned off for much longer than is desirable on a
> multitasking SBC. Use the 18S20's via an I2C interface chip instead.
>
> I'd advise looking carefully at risks versus benefits wrt the complexity of
> your project. Does taking wind speed and direction into account (for
> example) result in measurable benefit and what is the risk in terms of
> software complexity?
>
> If you want to go ahead, get yourself an evaluation kit and start playing
> and learning. This will help you understand the magnitude of the task ahead.
>
> HTH,
> Steve S

The majority of the OP's desired functions are available on commercial
heating control systems already. However theyre not cheap.

For the computer side of things, I would steer well clear of PCs, as
you need a system that will stay running for years at a time, and PCs
simply dont have the necessary hardware or software reliability. My
first choice would likely be a BBC B. If youre not familiar with them,
theyre 1982 32k 4MHz command line machines with inbuilt OS and BASIC,
and are stable as a rock. They also have lots of A./D I/O onboard, and
are easy to program, so are popular for scientific monitoring and
control projects. Despite being hopelessly out of date technically,
they still retain a niche market for these sort of apps. E-bay. Burn
your software to EPROM, and the EPROM plugs into the machine. Add
sideways RAM if you want more RAM, or get a BBC Master instead (128k).

And, as has been said, the system must fail to functional. If it
doesnt, youre buying yourself a whole lotta trouble downline, and
trouble costs money.


NT