Thanks - I checked out their site - A bit technical, but it seems that the
iButton line is aimed at temperature/humidity logging. I would also need to
know when compressor switches on and off - For this, I would ideally use
current measurement (0-10A DC), voltage (0-30V) or even something like
sound. Two temperatures would be better than one.

Because of this, the buttons made for monitoring transportation
temp/humidity, may not be the best choice. The multi port dataloggers would
be great, but cost is a bit high for a one time experiment. There are units
that interface with a computer that are aimed at school science projects
that are more reasonable, but my laptops CDROM just failed!

http://www.drdaq.com/

I would prefer a stand alone unit for data collection that I can connect to
my desktop computer for downloading. The Onset Hobo would do the job, but by
time software and sensors are added, it becomes a bit pricey for a 1 time
job.

GBM

wrote in message
ps.com...
Dallas Semiconductor sells temperature loggers as part of their iButton
line which can be placed wherever you want records. They come in a can
about the size of a quarter. You can also purchase a USB interface,
which you can connect the temperature logger into to get the data out
of it, and set the parameters to sample the data in the first place.
See http://para.maxim-ic.com/cache/en/results/4872.html for the USB
interface, and http://para.maxim-ic.com/cache/en/results/4871.html for
the loggers themselves.

Starter kits are available from
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2820; this kit for $60
includes the USB interface, and a thermocron (which might be for the
wrong temperature range). The thermocrons typically have a 10 year
lifetime.

I've strapped these to water heater output lines and watched the usage
patterns of hot water. Software for windows XP is free for download.
If you're trying to use this with Linux, try the "One Wire File System"
software.