Control of Central heating from PC - Thermostat Inputs - Relay outputs

[John]

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?

[AWM]

"John" <john@spam.me> wrote in message
news:BIYcb.980$wm7.8704210@news-text.cableinet.net... 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

[Mark]

Check these out for some ideas...

http://www.automatedhome.co.uk/article.php3?story_id=852
http://www.automatedhome.co.uk/article.php3?story_id=1209
http://www.automatedhome.co.uk/article.php3?story_id=1206
http://www.blackfirs.com/boiler.htm

M.

[Andrew Gabriel]

In article <bl1sd1$jhr$1@titan.btinternet.com>,
"AWM" <nothere@nowhere.freeserve.co.uk> writes: "John" <john@spam.me> wrote in message news:BIYcb.980$wm7.8704210@news-text.cableinet.net... 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

[awm]

Andrew Gabriel wrote: In article <bl1sd1$jhr$1@titan.btinternet.com>, "AWM" <nothere@nowhere.freeserve.co.uk> writes:
A few ways you can do this Picot do printer port data loggers than can beread directly into Excel spread sheets --- I've tried this and it works.Howerver a better way of measuring temperature is using Dallalssemiconductor DS18S20 temperature sensor, a selection of software forreading these is available off the net but you may find a combinatio ofAutom8it and Quasar electroics 3145 temperature logger the easiest andcheapest to get working.Linkshttp://www.picotech.com/data.htmlhttp://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).

Depends how much the error is, if its a lot it is back to an adc and
thermistor(s) which would need calibrated, it would be good to collect
boiler exhaust gas temperature also by sticking a thermo couple into it.

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]

In article <blbb79$6u0$1@hercules.btinternet.com>,
awm <thevillage@nohere.com> writes: Andrew Gabriel wrote: 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). Depends how much the error is, if its a lot it is back to an adc and thermistor(s) which would need calibrated, it would be good to collect boiler exhaust gas temperature also by sticking a thermo couple into it.

I rather imagine that if it reads, you'll get the right answer.
I don't recall the datasheet being specific on the failure mode.

What might happen is that it runs out of power partway through
transmitting back on the bus (as it's powered from a small internal
capacitor for this). Another possibility might be quiescent leakage
current through several 'hot' devices starts interfering with the
reading of all devices in the bus, reducing the number which can be
driven in parasitic mode on a bus. All just guessing though...

Also, bare in mind flue gasses can be quite corrosive if you try
measuring their temperature. I have a condensing boiler and the
condensate is similar acidity to vinegar (not measured it myself,
but that was mentioned somewhere in the blurb). Condensate
pipework must not contain any metal (except stainless steel).

--
Andrew Gabriel

[Andrew Gabriel]

Some other tips which are based on my experience of using DS18S20's...

Check the temperature you got back is reasonable. Glitches during
reading (probably interferance on the bus) often seem to return
readings of -88.8C or 85.0C, both of which I just treat as a misread
unless the previous reading was near that value. I also disregard
the odd reading which would imply, for example, the room jumped in
temperature by 20C in a few seconds for just one reading (I think
such a reading only ever happened once to me).

The device can oscillate, alternately returning readings of, say,
20.0C then 20.5C when the temperature is on the cusp. I ignore
changes of 0.5C for a period (a minute IIRC) to avoid the program
really thinking the temperature is oscillating every few seconds
when a new reading is taken. Another way would be to average the
temperature based on a decaying average of the past readings, but
that would be less responsive to genuine fast temperature changes.

(You can read temperature more accurately than 0.5C from the devices,
but it requires a different method and the controller I use doesn't
do this.)

--
Andrew Gabriel

[Robert L. Bass]

> Another way would be to average the temperature based on a decaying average of the past readings, but that would be less responsive to genuine fast temperature changes.

You might overcome that weakness by comparing the decaying average over say
15+ minutes to a shorter decaying average, say 3 minutes. Any time the
delta exceeds an acceptable range activate the air handler or whatever. The
logic is simple enough -- a few lines of code. Heat anticipation logic
could allow a slow-acting, hydronic or radiant system to activate before a
descending temperature reaches the limit and deactivate before the rising
temperature reaches the upper limit.

Regards,
Robert

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[Anthony Fremont]

Andrew Gabriel wrote:
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).

Note: Parasitic mode does not imply multiple devices on the line.
Parasitic mode means that you are really using only two wires and not
three (where the Vdd pin is tied to a high current voltage source
permanantly). In parasitic mode, the Vdd pin of the sensor is tied to
ground. Also in parasitic mode, the microcontroller must supply extra
power to the DQ line during a temperature conversion as the charge
stored in parasitic mode is too weak to accomplish this without it.

BTW, the 18B20 offers higher accuracy (<.5C) and precision (.0625 C).

michael

[mchiper]

In alt.home.automation, Msg ID: <BIYcb.980$wm7.8704210@news-text.cableinet.net>
"John" <john@spam.me>, wrote:
Dont ask why
Why Control a Central heating from PC?(I suspect I am over complicating matters somewhat)
I thgink you are.but I am thinking about attempting to control the central heating via pc.

I think, that you and the other's replying from the UK are the same person.
Without any design specs they are recommending hardware..
Amazing?
Build it first, then design it...
--
Ray