Interfacing with Hardware - where to start

I recently found a link to an Arduino based cat feeder (link below) and I'd like to make one myself (but a little differently and for 2 cats). I've always wanted to learn electronics and microprocessors and this seems like a good opportunity to learn. I have a very limited understanding of building circuits. However, I have extensive understanding of logic and writing programs (so writing the code should not be diffifult).

In my design so far I need to run 2 motors, need to program a clock (or use a library) into the Arduino and schedule feedings. And calibrate the motor running time for each cat to dispense the appropriate food.

What I don't understand is how the inputs are triggered. Is it just +5v on the input which causes it to trigger? How to I go about determining the voltages and resistances that inputs and outputs handle? Is there an online primer/tutorial which discusses how to interface various types of hardware directly with the Arduino?

http://andres-leon.blogspot.com/2009/04/my-first-arduino-project-diy-automatic.html

Is it just +5v on the input which causes it to trigger?

No, it could be 0V, or some analogue voltage.

I really wouldn’t suggest using the Arduino in a life-support role.

At the bottom of all Atmel data sheets is this warning:-

Atmel's products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life.

I take it you two aren't American? Haha :D The lazier we can be, the better! But I'm going to have to agree here, nothing is better than some TLC!

I really wouldn't suggest using the Arduino in a life-support role.

Lighten up, there just cats 8-)

Besides they have like nine lives or something ;)

Lefty

See, the key use here (at least in my perspective, and why I've been thinking about a similar project) is not to foist the sole responsibility for making sure the cats get fed onto the machine, but rather to divorce the cats' association of food with humans. Our cats are smart enough to realize 1) the human must be awake in order for them to get breakfast, and 2) climbing the curtains is an effective way of getting the human awake, particularly if you climb the set of curtains that are right above the human's head (you know, the ones that sometimes fall down when you happen to be climbing them).

I'm trying to imprint the association of waking the human up with pissed-off human tosses you out of the bedroom and shuts the door (they hate that, and the incessant meowing is slightly more tolerable than a cat landing on your face, trust me) to mitigate that second part, but, well. . . I guess you can only handle so many associations when your brain is the size of a walnut.

So with a bit of redundancy you can make the system reliable enough for everyday use, especially considering that most cats WILL LET YOU KNOW if they haven't been fed recently enough. Of course, relying on something like this to feed them over a two week vacation is another matter entirely.