Basically, I'm working on an environmental controller system. The humidity sensor is one of those capacitive types that puts out a square wave, I think from 5-10 KHz, with the signal around 3v, 50% duty cycle. Right now my program is set up to poll sensors and user inputs rapidly, but there's nothing more frustrating than pressing a button and waiting for a second for a cursor to move, for example. I want the system to poll each sensor once a second and the user inputs at several times that rate, but at the same time, I'd like the program to be constantly reading the frequency of the humidity sensor so that a reading is Just Available when I want it.
Right now I've got it hooked up to a cheap DS1307-based RTC, so I do have a 1Hz square wave output to work with, and I'm thinking of upgrading to a more precise RTC with a 32KHz output, if that helps. I can generally get what I'm working on working, eventually, as far as programming goes, but I've got no experience with working close to the bare metal of an ATMega.
I do have flip-flops and and some other basic logic laying about, so if worst comes to worst I guess I could offload most of the frequency counting on hardware.