I would like to build an automatic water faucet, but wasn't sure what the sensor in a unit like the one below consists of. Here is a sample picture:

http://www.airdelights.com/images/au...ts/sf2300a.jpg

What kind of sensor do these faucets use? Would it work well outside?
I'm thinking of building an automatic water fountain for my dog which would consist of mostly everyday parts. The goal is to take a sink fixture and mount it upside down or sideways so the dog can reach it easily. The water source would likely come from inside and be slightly elevated from the exit point. The reason is so that once the valve has shut off the water will drain out and prevent freezing.

 

most probably its an IR proxy sensor.

 

The water foundtains at my college are IR I think. They don't work when I'm wearing my black leather coat, have to hold my hand up to it then. lol
~Mike

__________________
All Electronic components run on smoke. Let the smoke out and it no longer works.
~Tim Baker (Electronics Instructor at John A. Logan College)

 

How about keeping it simple and putting a magnet on the dogs collar ?

 

Your sink on the side idea might be frustrating for your dog. As you know dogs need a bowl or puddle of water to drink from (they lap the water up with their tongue). Running water from a faucet is a challenge for them. While I understand that you do not want to let the water freeze you may have no choice other than fitting a water bowl heater.
As to how to fill the bowl automatically your dog can be trained to push a plate with its muzzle that opens the tap. Light beams, magnets, proximity sensors just add an extra degree of failure with their complexity.
Klaus