Re: Temperature monitoring

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Sat, 10 Mar 2007 06:20:32 +0000 (UTC), Dave Close <dave@xxxxxxxxxxx>
wrote in message  <esting$m2h$1@xxxxxxxxxxxxxxxxx>:

>I'm seeking to buy or build several temperature monitoring devices. I
>don't want intelligence, just reporting. All I want to do is to collect
>the information and record it.
>
>I can buy an "atomic clock" with a remote temperature sensor for about
>$20. Most of that cost is for the clock, not the sensor. But when I look
>for a similar device that can send data to a computer, prices quickly go
>(way!) above $100. Either this is a missed market opportunity or I'm
>just not looking in the right place.
>
>I'd like the remote sensor to transmit its data either wirelessly, via
>X10-like power line signaling, or over a simple three-wire phone cord.
>Its reports should be periodic, say every five minutes, or on command.
>The report should be the ambient temperature to a half-degree C and the
>id of the sensor.
>
>I have found some devices that can be programmed to take some action
>when the ambient temperature falls outside some boundary. I don't want
>any action taken except to report the temperature, not just when its low
>or high but all the time.
>
>What have I missed?

How many sensors? You have apparently have  a <$100 budget so this is an
important question.

What temperature range?  10-30C (ambient "room" temperature) or -40C to 60C
(full range ambient including (eg) hot attics)?

How far apart do the sensors need to be? All in one room or throughout a
house?

Why does the report have to initiated by the sensor rather than the
conventional approach of polling by the recording device?

What device will you use to store the data? If not a PC, how will you
use/transfer the data once it is stored?

You can easily make what you want (self reporting) for about $5 per sensor
if you would be willing to learn to program microcontrollers.

I'm currently enamored of the  Atmel ATtiny-45, an 8-pin AVR
http://www.atmel.com/dyn/resources/prod_documents/2586S.pdf
 microcontroller the size of fingernail that has 10-bit analog inputs other
I/O and is ~60x faster (20 MIPS) than the original IBM PC 0.3 MIPS). It can
run on as little as 1.8 volts and 300 microamps (and 0.1 microamps when
sleeping).  It can be programmed using BASCOM for which a free version is
available http://www.mcselec.com/ It costs about $2 from www.digikey.com

Or check out the PICAXE
http://www.rev-ed.co.uk/picaxe/

especially Peter Anderson's offerings
http://www.phanderson.com/picaxe/
http://www.phanderson.com/picaxe/picaxe_overview.html

and this $8 kit in particular
http://www.phanderson.com/stamp/onewire.html

The Maxim / Dallas 1-wire technology meets your needs and budget if you are
willing to do some minor soldering and construction and *IMPORTANT* you use
Cat5 wiring instead of "phone wire" by which I understand untwisted (eg)
"satin" cord.

http://www.maxim-ic.com/1-Wire.cfm
www.phanderson.com/

There are also temperature sensors with voltage output such as the LM34 and
LM 35 that can be read by any of a bajjilion different devices/loggers with
8-bit or better analog to digital converters including (eg) an old or new
PC.
http://www.national.com/pf/LM/LM35.html

Or simple thermistors which can be extremely accurate but typically require
signal conditioning, and for wide ranges,at least 12-bit analog to digital
converters.

HTH ...Marc
Marc_F_Hult
www.neuralhome.info