Wire length

I got comment from Stephane about wanting to know, how long CAT5E ethernet cable can be used. Well, I just bought a 100 meters (328 feet) of wire. Not CAT5E ethernet cable, but 4 wire flat telephone cable. I connected one temperature sensor DS18S20 at one end and DS9490R USB adapter to another. Under /media/1wire/ folder I got new folder "10.BCD8ED010800" and I got even a reading from it.

$ cat /media/1wire/10.BCD8ED010800/temperature
      23.375
$ cat /media/1wire/10.BCD8ED010800/power
0

power file shows that it's powered parasitically.

I don't know how many sensors I can connect to 100 meeter cable before I have to add additional power, but if I got reading from 100 meeter cable, then I am sure I get readings of many sensors with external power. Just found guidelines page. In my case, I probably need total of 50 meters of wiring.

Reading 2 sensors

So, I have connected 2 sensors and reading these for about 5 days now. One is outside the window (yellow) and another is connected to radiator (red). I made even a script that reads sensors every 10 minutes and sends reading over internet to public net and saves it to MySQL database. And using XML/SWF Charts, I can see live chart on readings. First problem I noticed right away is outside sensor. Currently here in Estonia, outside air temperature is around 10°C, but sometimes sun comes out and heats outside sensor up to about 25°C. That means that I have to find some better place for this sensor, where sun can't shine on it. Also, I think I should rewrite my script so that when reading outside sensor, then on saving it to database, It should save average value of current and last two readings.
Here is another chart, where temp1 is live reading of outside temperature and temp2 is average of last 3 readings. As you can see, temp2 is little bit smoother.

About my radiators, I found out that they are switched off for night. Every day 23:10, they are turned off and temperature starts to fall. And from 6:10 they are turned on and temperature rapidly raises. I am thinking that if I want some more energy efficiency, then I would also turn off radiators from 9:00 on working days and turn them on on 16:00, about hour before I'm home.

first readings

So, Yesterday I installed owfs and got first read. I made a little script that read sensor every 15 minutes and wrote it to file. Here is my living-room temperature from 22:00 30.09.2009 to 18:30 01.10.2009.
I took out my old laptop, about 5-6 year old with 1,2GHz and 256MB RAM. Useless for everyday use, perfect for server type use. Currently it has some kind of Windows installed, but I found live CD with owfs. ISO file is less then 50MB and I have to say that it worked quite well, but I will probably find something better to install.