Automated Chicken Feeder

My roommates and I started keeping six chickens in our backyard last May.  We've raised four Buff Orpingtons, and two Easter Eggers that are likely Ameraucana cross-breeds.  I'd like to think that our chickens can be an economically and environmentally sensible thing for us to do, which means no overpriced commercial coop, very limited use of new materials, extending their feed with kitchen scraps, and generally taking every opportunity to minimize the amount of attention they need.

Today, we feed our six chickens with an open dish.  If there's feed left in the dish at the end of the day, it will attract rodents.  To avoid this, every morning the bowl is re-filled with one day's worth of feed.

To eliminate this chore, I'm going to build a simple and robust automated feeder.  The goal is to refill the feed less than once per week, without adding too much complexity to the entire system.

Since the chickens live in a pen that's well away from our house, or any exterior outlets, we'll need the automated feeder to be self-powered.  Since it's going to live outside for years, it needs to be designed to handle sun, rain, and dirt without maintenance work.

My first thought was to reference designs for cold-frames that open and shut using bimetal springs or hydraulic mechanisms filled with kerosene (which has a high thermal expansion coefficient).  This might be workable -- since the ambient temperature where we live is quite stable, concentrated sunlight could create significant daily variations in temperature.  A chicken-powered chicken feeder could make a workable mechanical base for this type of passive control system.

A more direct approach would be to directly sense ambient light levels, and open/shut the feeder based on that sensor reading.  A ready-made platform like the Arduino would make this easy, but seems like an inelegant level of complexity and power consumption for such a simple application.

For this project, I'm shooting for something that's easier to tune than a fully passive mechanical system, but more elegant than breaking out an entire microprocessor.