Re: suggestions for air temperature measurement

[andrew@xxxxxxxxxxxxxxxxxxxx (Andrew Gabriel)]

In article <8vW7f.48$9V6.654@xxxxxxxxxxxxxxx>,
	"AZ Woody" <Reply@xxxxxxxxxxxxxx> writes:
> Sounds to me that 1-wire might be the way to go.  A two wire buss could
> support the sensors, and a $20 adapter for the computer. (use a full cat 5
> for distance, and to provide for expandability.)

They're cheap, and if the location will be inaccessible, I would
put in two of them, each on a different pair, so that if one dies,
you can switch to the other.

> Dallas provides some good sample code on their website for interfacing
> Doing a "parasite" read on a sensor can be done on a single sensor in about
> a second, Each sensor has a unique ID, and the bast part is, I've gotten
> them for <$3 each in to-92 cases.  So, if you got 15 sensors, you can read
> them about 4 times a minute if you want.  They're good to +/- 1 degree c or
> +/- 2 degree C based on the specific sensor

The DS1820's are accurate to fractions of a ºC, although it's
complicated to read them any more accurately than 0.5ºC (and
might not be possible in parasitic power mode -- not sure on that
point).

> You can build sw on windows and Linux for sure (those are the only two I've
> done)
>
> I'm currently monitoring temps in my HVAC system, outside temps, and even
> have one mounted in a "can cooler" near my computer that will alert me if my
> beverage gets too warm.

Here's a section of logging from my system (running on Solaris x86)...
Oct 27 16:13:48 Temperature - Outdoors           18.0
Oct 27 16:14:37 Temperature - Freezer           -23.0
Oct 27 16:14:37 Temperature - Fridge              4.5
Oct 27 16:15:48 Temperature - Freezer           -23.5
Oct 27 16:16:21 Temperature - Loft               24.5
Oct 27 16:17:05 Temperature - Freezer           -24.0
Oct 27 16:18:32 Temperature - Freezer           -24.5
Oct 27 16:20:05 Temperature - Fridge              4.0
Oct 27 16:20:21 Temperature - Freezer           -25.0
Oct 27 16:22:22 Temperature - Freezer           -25.5
Oct 27 16:27:05 Temperature - Freezer           -25.0
Oct 27 16:27:55 Temperature - Fridge              3.5
Oct 27 16:28:55 Temperature - Freezer           -24.5
Oct 27 16:30:49 Temperature - Freezer           -24.0
Oct 27 16:32:49 Temperature - Freezer           -23.5
Oct 27 16:35:17 Temperature - Freezer           -23.0
Oct 27 16:37:47 Temperature - Freezer           -22.5
Oct 27 16:38:19 Temperature - Fridge              3.0
Oct 27 16:38:44 Temperature - Loft               24.0
Oct 27 16:41:01 Temperature - Freezer           -22.0

--
Andrew Gabriel