I'm using Arduino for some months and have a lot of fun, I'm learning electronics this way.
I already control some stuff in our farm based (some time) on temperature. I'm using Dallas DS18B20.
Now, I'm looking to control heating light based on temperature to install in many place (about 10). I'm looking for the cheapest way to connect a DS18B20 instead of a full Atmega168/368 Arduino, I'm looking for another Atmel if possible, a smaller one compatible with Arduino IDE.
Thanks,
Keven
search the fourms for attiny 85 (8 pin dip) or 84 (14 pin dip) which with little effort can be setup and running with the arduino IDE
also look around for mini, nano and other SMD based arduino's which is a plug n go solution about the size of a stick of gum
I maybe want to use Attiny
I maybe want to use Attiny
That's my first choice.
Ok but if we forgot Arduino and Atmel. In electronic what is the simple way to connect a DS18B20, do we need a MCU ?
Check out the RBBB: buy a 5-pack of bare boards, some pre-programmed ATMegas, and score the parts either from Modern Device or Mouser (you've been lusting after some specialized chips anyway, right? ;)). You'll wind up with 5 Arduinos extremely well-suited for permanently building into projects, for about $12-15 apiece.
You'll also need to buy an interface board to either level-shift the TTL to RS-232, or do USB to TTL serial (also pretty cheap), so you can download sketches to them. But many projects don't need a PC interface for anything other than code changes, so not having the parts cost and board space for one can actually be a big plus.
But how it's possible to buy a device that will do it for 5$ ???
Ok but if we forgot Arduino and Atmel. In electronic what is the simple way to connect a DS18B20, do we need a MCU ?
You'll need something that communicates via 1-Wire. Other than some sort of processor, I can't imagine what else would work.
So what is the cheapest processor that can be used for this kind of simple task?
well what exactly do you want to do with temperature readings ? sompare it against a set value and if < or > switch on something ? Then http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1290447100/5
i didnt try it out as of now ( exams 
)
Some details: I want to have (possibly) a DS18b20 that monitor temperature and turn on/off an heating lamp according to ambient temperature. If temperature cool down to a certain point turn ON the light, if temperature get too hot, turn OFF the lamp. Is simple as that.
But I don't want to have a 40$ device to do that since we can find 5$ one in store. I took that building it should be less expensive, it seem I'm wrong
building a 1 off vs mass production
even if you used a tiny85 your looking at about 3 bucks just for the chip, and you need power regulation, capacitors, something to switch your lamp, a board to mount it on etc (+ shipping)
I'll do it on my own anyways Just for the fun of it.
Just buy one thermostat...
Be careful with the "just for fun" approach. I have a chicken coop with like $150 worth of electronics in it now due to a "just for fun" project. What did you find for $5? I'd like all of my hardware back from the coop if it's that simple. 