In article ,
"AWM" writes:

"John" wrote in message
...
Dont ask why (I suspect i am over complicating matters somewhat) but I am
thinking about attempting to control the central heating via pc.

To do this I need to take two tempreature readings (flow and return) and
feed this information to the PC (the capacity for a third room thermostat
would be useful for later usage)

Outputs would need to control two relays which would switch the heating
accordinly.

As the processing is mostly mathematical, the easiest system to use (this is
a prototype) would be something like Excel, rather than having to writing
dedicated software. Ideally, the imput readings would be displayed in a
cell, and outputs can be switched depending on the value in a second
calculated cell.

I am sure that this should not be difficult with the right hardware? Is it
more diffult that it sounds?

Are there any suitable low cost data input output boards that would help?
Any links?

A few ways you can do this Picot do printer port data loggers than can be
read directly into Excel spread sheets --- I've tried this and it works.
Howerver a better way of measuring temperature is using Dallals
semiconductor DS18S20 temperature sensor, a selection of software for
reading these is available off the net but you may find a combinatio of
Autom8it and Quasar electroics 3145 temperature logger the easiest and
cheapest to get working.
Links
http://www.picotech.com/data.html
http://autom8it.com/
http://quasarelectronics.com/computer_projects.htm

Another link: http://www.phanderson.com

I am using one of Phil's modules to read 3 DS18S20's (upstairs,
downstairs, outdoors) and two analogue inputs (upstairs and
downstairs potentiometers as room stats) to control a two zone
heating system. I have been thinking of attaching DS18S20's to
the flow and return, although the Dallas datasheet says they
may not work well in parasitic mode at high temperatures due
to increased current leakage inside the devices, and Phil's
module does drive them in parasitic mode (multiple devices on
a single cable pair).

Phil's module provides the data over an RS232 serial link, which
I access with a purpose designed program (which I'm still working
on). In Windows, you would probably need to write a program to
interface between the serial port data and Excel.

--
Andrew Gabriel