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Posted by Mike Scaife on July 8, 2007, 12:08 am

Hi Jeff

I use the PicAxe range of PIC based micro-controllers, they are very easy to
program in mini-basic and have full IO, analogue, 1 wire bus commands
already built in. They start at 8 pin up to 40 pin devices. They should be
available in USA

Here is a link http://www.picaxe.orcon.net.nz/  that points to most of the
info available. For measuring temperatures they use the DS18B20 temperature
sensor chips.

Mike Scaife (NZ)

Posted by Logan Shaw on July 6, 2007, 6:03 am
Jeff wrote:

When engineers design custom control systems for industrial applications
(like factories, water treatment plants, etc.) they use PLCs (programmable
logic controllers).

These are little bitty special-purpose computers design to do simple
control tasks like this.  They have a dead simple design (no operating
system to speak of, etc.) and they have built-in analog and digital I/O
(inputs for reading sensors and outputs for controlling things like
switches).  Some of them are modular and allow you to plug in additional
I/O units.  Most of them are programmed over serial port or USB.
Because they are so simple, it's pretty easy to get them to work reliably.
There is no operating system (or not much of one) to crash, and so on.

There are several sites that sell PLCs, ranging from cheap to really
expensive.  You can get cheap ones (that would suitable for home use)
at http://www.automationdirect.com/  .  Specifically, here:


If you decide to go this route, keep in mind that the hardware has
limits on maximum number of I/O points, and to get beyond a certain
number of points of I/O, you eventually have to go to a more expensive
model.  So do your planning with that in mind.

Another option sort of along the same lines as a PLC is that you can
get I/O modules that run on Ethernet.  Many of these are designed to
operate with PLCs that have Ethernet ports.  I don't know if they can
work with PCs, because you would need software to speak whatever
protocol they use.

   - Logan

Posted by bowgus on July 6, 2007, 11:43 am
Fwiw ... I find that a central heat/vent system ... or a whole house
approach ... (if you can have one or can install one) works just fine
for me. Right now I'm in the basement with the forced air furnace fan
turned on pulling the cool air out of the basement and moving it
through the house ... else it would be too cool and the air too
"stale" down here. I could add a fresh air intake/stale air output to
the system but so far there's no need ... just leave a few windows
open overnight.

And there's no possibility of a hassle with insurance, inspections, as
the system is approved ... unlike any kludges comprised of a PC,
controllers, sensors, wiring, and fans that one might come up with.

And fwiw, I once had a bathroom vent fan catch fire ...

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