Hi there, I made a simple project a little while ago. It didn't work just yet but it is now.
For some reason I ended up with a chicken and temperatures that dropped to -18 at night. Long story. It took the drinking water less then an hour to freeze and since there isn't someone arround all the time I had to help the poor beast. At least next year that is :)
I started out with this thing:
It's basically a relay switchable by picaxe, a 12v to 5v voltage regulator (take the right one, I screwed up in a silly way here, thanks Geir). It also has a diode (front corner) which alows me to hook up solar panels and charge the battery). In addition I got these of ebay "Motorcycle Heated Grip Pads for Handlebars" (6$)
I stuck the above to a regular drinking bottle for birds (they have glue on 1 side, easy does it) and then covered the bottle with isolation foil. All together it looks like this:
It draws about 900mili amps and the relay can handle 1 amp (at a higher voltage). Then there goes a thermometer (LM35DZ) to the bottom of the bottle again isolated. I stuck this right to the bottom and hotglued it tightly to make sure i get the water temperature and not the outside temp.
And all together it looks something like this:
So there you go, the picaxe measures the water temp, if it gets below 3 degrees it turns on the heater if it gets above it turns off the heater. It has a 12v battery from an old UPS that's being charged by the solarcells.
What I would improve next year is adding an LDR so it knows when it's dark. Chickens are off to bed when the sun goes down so that would save the battery (I just guess, maybe it will take more power to heat up a block off ice in the morning).
Be good to your chicken, you might need it for your next "tracking" project;