Can't resist posting this.
On successive days I saw a squirrel and a feral cat getting water by licking ice in our backyard.
To provide a source of drinking water for all the assorted wildlife living out there or passing through, I built this heated water bowl.
A thin-film heater that I got as a trade show sample years ago and a TMP 37 temperature sensor are attached to the underside of a small, cheap stainless steel pet food bowl using Kapton tape.
A Duemilanove reads the sensor on A0, controls the 6.7 volts to the heater using an FET driven by D3, really all I changed in Brett Beauregard's excellent PID library sample code was the math to change from TMP 36 to TMP 37.
Water consumption and tracks found in snow indicate that a source of liquid water in midwinter is becoming very popular.
I thought of an automatic water-feed, but the freezing conditions would require a heated line and that just added too much complication for a project I wanted to deploy quickly. Definitely in the works for next winter, though. Same for the motion detector camera.
I have seen squirrels, a cat, and birds drinking in daylight hours ... heard sounds in the night, and seen lots of various tracks (raccoon and skunk for sure, maybe opossum) when there is fresh snow in the morning. Lots of takers too, the bowl typically needs refilling 2 or 3 times in 24 hours.
Answers to questions above, not necessarily in order ....
Not a Peltier device, just a resistance heating element, 7.2 ohms, made from fiberglass and silicone rubber. The board on the left is an old linear power supply , modified to provide 6.7 volts DC, up to 3 amps.
a few data points on power consumption;
during bench testing back in January, Arduino + heater drew 1.9 amps at 6.6 volts DC
Arduino + heater + power supply measured yesterday with a P3 Kill-a-watt, 4 watts idle, 12 watts full load . Version 2 will probably include a data logger.
Oh, and so far no cats (or anything else) have been electrocuted !
Chewing on the line cord is about the only option for that, the cheap plastic enclosure has held up pretty well overall.